ASME Conference Presenter Attendance Policy and Archival Proceedings

2016;():V001T00A001. doi:10.1115/ES2016-NS1.

This online compilation of papers from the ASME 2016 10th International Conference on Energy Sustainability (ES2016) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Biofuels, Hydrogen, Syngas, and Alternate Fuels

2016;():V001T02A001. doi:10.1115/ES2016-59047.

A work on the comparative analysis of selected substrates for biogas production using a developed digester is presented. The substrates utilized include cow dung and vegetable waste. The developed digester has 60 litres of substrate volume, incorporates ease of stirring the slurry and mobility of the digester within the farm. The digester was charged with cow dung and vegetable waste respectively with water in a ratio 1:2 at a mesophilic temperature range (20°C – 45 °C) for thirty days retention time and comparative yield within the same operating conditions was studied. The results obtained from the gas production showed that cow dung produced a cumulative biogas yield of 0.702 litres while vegetable waste produced a cumulative yield of 0.144 litres. This result showed that these wastes could be a source of renewable gas if operated on a large scale, while simultaneously reducing environmental pollution particularly within a farm. Also, the results highlight the selection options available to a rural farmer in terms of yield.

Topics: Biogas
Commentary by Dr. Valentin Fuster
2016;():V001T02A002. doi:10.1115/ES2016-59095.

On-board hydrogen production via catalytic autothermal reforming is beneficial to vehicles using fuel cells because it eliminates the challenges of hydrogen storage. As the primary fuel for both civilian and military air flight application, Jet-A fuel (after desulfurization) was reformed for making hydrogen-rich fuels in this study using an in-house-made Rh/NiO/K-La-Ce-Al-OX ATR catalyst under various operating conditions. Based on the preliminary thermodynamic analysis of reaction equilibrium, important parameters such as ratios of H2O/C and O2/C were selected, in the range of 1.1–2.5 and 0.5–1.0, respectively. The optimal operating conditions were experimentally obtained at the reactor’s temperature of 696.2 °C, which gave H2O/C = 2.5 and O2/C = 0.5, and the obtained fuel conversion percentage, hydrogen yield (can be large than 1 from definition), and energy efficiency were 88.66%, 143.84%, and 64.74%, respectively. In addition, a discussion of the concentration variation of CO and CO2 at different H2O/C, as well as the analysis of fuel conversion profile, leads to the finding of effective approaches for suppression of coke formation.

Commentary by Dr. Valentin Fuster
2016;():V001T02A003. doi:10.1115/ES2016-59164.

The depletion of fossil fuels and its emissions promoted the researchers to search for substitute fuels and their controlled combustion. Hydrogen is considered as one of the best fuels for internal combustion engines because of its unique combustion properties. Currently, there are very few commercial devices that utilize hydrogen combustion for the production of heat, which is mainly due to the limited availability of hydrogen fuel. As the accompanying environmental legislation will clearly favour clean technologies, the emergence of hydrogen as an energy carrier will modify this situation. To achieve controlled combustion, an attempt was made at investigating the effect of change of piston geometry on the emission characteristics of diesel engine enriched with hydrogen at optimum flow rate. Experiments were conducted to study the effect of varied piston bowl geometry on the emission characteristics of diesel engine enriched with hydrogen at a flow rate of 6 lpm on four stroke single cylinder diesel engine at constant speed of 1500 rpm for different loads. For flow rates above 6 lpm knocking tendency was observed due to raise in temperature and peak pressures with addition of hydrogen. The experiments were conducted with standard hemispherical, toroidal and re-entrant toroidal piston bowl geometry at 6 lpm flow rate of hydrogen duly ensuring the same compression ratio in all three cases. The emissions for diesel engine enriched with hydrogen in hemispherical combustion chamber at 6 lpm flow rate were reduced by 27.1%, 37.5% and 10.8% of unburnt hydrocarbons (UHC), Carbon monoxide (CO) and smoke density respectively when compared to diesel fuel alone operation at rated load. This is mainly due to high combustion temperatures which lead to complete burning of fuel and reduction in carbon content with addition of hydrogen. However, there was a 14% increase in oxides of Nitrogen (NOx) emission due to high combustion temperatures by hydrogen induction. With toroidal and reentrant geometry of the combustion chambers at 6 lpm flow rate of hydrogen, the emission parameters were further reduced notably. Further there is an increase in NOx emission was observed in dual fuel mode compared to standard piston due to high cylinder temperatures and pressures. The obtained results show that at part load conditions with enriched hydrogen, the percentage reduction of NOx emission was engine load dependent, being least increase at low loads and high increase at high loads. The reduction in emission particulates with varied combustion chamber bowl geometry was due to improved swirl motion of high turbulence of air in the combustion.

Commentary by Dr. Valentin Fuster
2016;():V001T02A004. doi:10.1115/ES2016-59433.

In order to achieve the international climate goals and to keep the global temperature increase below 2 °C, carbon capture and storage in large point sources of CO2 emissions has received considerable attention. In recent years, mitigation of CO2 emissions from the power sector has been studied extensively whereas other industrial point source emitters such as hydrogen industry have also great potential for CO2 abatement.

This study aims to draw an updated comparison between different hydrogen and power cogeneration systems using natural gas and coal as feedstock. The goal is to show the relative advantage of cogeneration systems with respect to CO2 emission reduction costs. Accordingly, the Reference Case is selected as a large-scale H2 production system with CO2 venting using natural gas based on steam methane reforming. In this work, H2 and electricity cogeneration with CO2 capture based on auto-thermal reforming of natural gas has been simulated using ASPEN Plus™, while the cost and performance indicators for the plant based on steam methane reforming of natural gas and the coal-based plants have been adopted from the literature. Using a consistent approach, different plants are compared techno-economically. A sensitivity analysis has also been performed with variation in the most important input parameters including natural gas price (2–8 $/GJ), coal price (1–4 $/GJ), electricity price (30–90 $/MWh) and capacity factors (85–50%) and the results are presented here.

The results demonstrate that the total efficiency of the system is slightly higher in natural gas-based systems than in coal-based systems. The results also indicate that although H2 production cost increases with power cogeneration and CO2 capture, cogeneration is a promising and attractive alternative for clean power generation. The highest sensitivity of the results has been observed for the fuel price.

Commentary by Dr. Valentin Fuster
2016;():V001T02A005. doi:10.1115/ES2016-59530.

This study investigated the economic feasibility of distributed or decentralized torrefaction bio-refining using corn stover feedstock to generate value added products. Distributed bio-refining systems would be able to operate on private farm and commercial scales, eliminating the need for large capital investment for large processing facilities and decreasing logistical concerns for harvesting and marketing corn stover. A techno-economic model was developed to analyze the economics of harvesting techniques, logistics, processing requirements, and end product utilization. With the model, a base case analysis was established to analyze average values and to create a basis in which to compare a variety of economic scenarios. A sensitivity analysis was also completed to investigate outcomes based on variability of crop yields and product price, as well as costs associated with harvesting stover, input for operating the torrefaction system, and capital costs of equipment. Results of the analyses were quantified with respect to input costs required to generate torrefied products, potential profit of processed products, and the payback period of the production and conversion system. Preliminary results indicated that processing corn stover feedstock within a distribution torrefaction bio-refining system had high potential, in terms of economic feasibility, over a wide range of scenarios. Results indicated that payback periods as low as five years were possible under a wide variety of applications and operating costs. In addition to operating economically, it was also shown that end products could have increasing profit potential as a value added product.

Commentary by Dr. Valentin Fuster
2016;():V001T02A006. doi:10.1115/ES2016-59535.

Human activities like fossil fuel retrieval, biomass burning, waste disposal, and residential and commercial use of energy are continuing to effect the Earth’s energy budget by changing the emissions and resulting atmospheric concentrations of radioactively important gases, aerosols, and by changing land surface properties. These activities negatively contribute to Earth’s greenhouse gases including water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3). Approximately 82% of greenhouse gases are developed from the United States, Asia, and Europe alone. Food and their extraction processes, including transportation of those extracts, account for about 35% of those greenhouse gases. This includes wasted, rotten, and uneaten food. About 40% of food in the United States today goes uneaten, resulting in more than 20 pounds of food per person every month. Not only does this mean that Americans are throwing out upwards of $165 billion each year, amounting to $1,350 to more than $2,275 annually in waste per family of four, but also 25 percent of all freshwater and huge amounts of unnecessary chemicals, energy, and land. Moreover, almost all of that uneaten food ends up rotting in landfills. This number has increased, in regards to organic matter, from approximately 16 percent of U.S. methane emissions in 2010 upwards to 25 percent in 2012. With the increase in supply and demand of food, in addition to the lower consumer cost, the statistics of wasted feedstocks are rapidly increasing. The purpose of this research is to utilize wasted food to extract natural hydrocarbon oils through thermal depolymerization in order to develop an alternative fuel. Thermal depolymerization is a hydrous pyrolysis process that breaks down long chained polymers into simpler compounds and light hydrocarbons, much of which can be separated and used for fuel. Polymers include essentially all organic matter i.e. matter made of living or once-living things, which include petroleum products like plastic, styro-foam, and nylon, as well as plant and animal material, and manure. Potatoes and corn starch were used as feedstocks for this research and thermal depolymerization was conducted on the feedstocks for analysis and fuel collection. With optimum use and a mature thermal depolymerization technology, the Earth might comfortably support 10 times its current population at a high standard of living. There is enough biomass existing now accessible on the surface of the earth to provide 100 years of human energy use.

Topics: Fuels , Food products
Commentary by Dr. Valentin Fuster
2016;():V001T02A007. doi:10.1115/ES2016-59601.

Fast pyrolysis is one method of creating bio-oil from biomass such as native prairie grasses, corn stover, and other organic commercial and industrial byproducts. In this study, fast pyrolysis of camelina (Camelina sativa) meal feedstock was performed in an auger-type reactor. End products of the processing consisted of bio-char and condensed vapor in the form of bio-oil (ranging from liquid to highly viscous tar-like products). The bio-oil produced in the reactor was collected and analyzed to determine the effects of reactor and condenser temperatures on the properties of the bio-oil produced. Five reactor temperatures and two condenser temperatures were investigated in this study. The rheological properties of the bio-oil samples were analyzed, water content was determined with the Karl Fisher method, energy content was measured with a bomb calorimeter, and acidity was determined using a total acid titration test. The aging characteristics of the bio-oil were also investigated at seven days, fourteen days, and twenty-eight days after the oil was created to determine what effect, if any, time had on the its properties. Preliminary results indicated that products of the camelina meal pyrolysis process were more uniform when compared to that of other feedstocks (e.g. carinata meal, corn stover), yielding more consistent bio-oil characteristics.

Topics: Augers , Pyrolysis
Commentary by Dr. Valentin Fuster
2016;():V001T02A008. doi:10.1115/ES2016-59625.

A unique photobioreactor (PBR) constructed with acrylic sheet was used to grow S. Leopoliensis in 3.36 litters of Scully’s growth media. The PBR width was 51mm with a 273mm length and a growth media depth of 271mm. One of the PBR unique features was that it used a plenum and a porous membrane to inject air enriched with carbon dioxide into the growth medium. The HDPE (high-density polyethylene sintered beads) porous membrane served as the barrier between the reactor volume and the mixing plenum of the PBR. The air bubbled up through the porous membrane into the reactor volume with the growth medium mixing the contents of the reactor volume and transfer oxygen and carbon dioxide between the growth media and the bubbles. The second unique feature of the PBR is that it incorporated light guides in the design. The light guides were acrylic rods 9.5mm in diameter and a length projecting into the reactor volume of 38.1mm. The guides did not touch the opposite PBR wall. The light guides were abraded with sand paper on the outer to enhance light transfer from the guide to the growth medium. There were eight rows of light guides on each of the two PBR walls that were 273mm in length. Each row consisted of eight light guides space 34.1mm apart and 17.1mm from the side (short) walls of the PBR. Light was provided by two LED panels with 384 LED lights on each panel. The light from the panels had a wavelength of 650nm. The Light guides protruded through the PBR wall and light from the LED panels entered the light guide ends or transferred through the wall directly into the PBR reactor volume. The light guide ends occupied approximately 16% of the PBR wall area lit by the LED panels. The PBR produced 7.1g per litter of algal biomass in a 14 day growth cycle which encompassed a 3 day lag phase. The light guides disrupted the bubble flow pattern not allowing an obvious riser and/or downcomer to develop in the reactor volume. The disrupted flow pattern enhanced mixing and gas transfer. The enhanced mixing rotated the algal cells from more to less areas of the reactor volume more often aiding photosynthesis in a manner similar to flashing lights.

Topics: Membranes
Commentary by Dr. Valentin Fuster
2016;():V001T02A009. doi:10.1115/ES2016-59628.

A photobioreactor (PBR) was operated for sixteen days producing S. Leopoliensis. The PBR was lit by two LED panels, one on each of the long sides of the PBR. The PBR dimensions were nominally 51mm by 273mm with a height of 319mm (273mm liquid depth). Each LED panel was powered at 14.1W (11.2V and 1.26A). Measurements of ambient temperature, ambient relative humidity, water loss from the PBR, relative humidity of the exhaust gas from the PBR, air flow rate through the PBR, air pressure in the plenum, growth medium temperature, and LED panel temperature were made approximately daily. Measurements show that the growth medium (water) temperature was relatively insensitive to the ambient temperature which varied from 22.7C to 33.6C. The medium temperature ranged from 23.9C (beginning of the test) to 40.6C. The medium temperature mirrored the LED panel temperature staying 2–4C below the LED panel temperature after the first day. The elevated LED panel temperature was likely due to the inefficiency of the LED lights and the fact that much of the light passing through the reactor volume was incident on the LED panel on the opposite side of the reactor. The panels are black in color and absorbed a significant portion of the light passing through the reactor volume. The air flow rate through the PBR ranged from 1.33×10−5m3/s to 1.67×10−5m3/s. The parallel between panel temperature and PBR medium temperature indicate that the amount of air moving through the PBR was insufficient to affect the medium temperature significantly. The heat loss from the PBR to the ambient environment was also small likely due to the small area available to heat loss to the environment when the PBR walls with the LED panels are excluded. The LED panels covered nominally 88% of the PBR reactor volume area. The measured data and measurements of light intensity passing through the two short walls of the panel will be used to estimate heat loss parameters of the PBR. The exhaust air from the PBR varied from 42.6% to 99.1% with the higher measurements occurring days 6–11. Estimates of the energy stored in the algal biomass are also evaluated in the analysis.

Commentary by Dr. Valentin Fuster
2016;():V001T02A010. doi:10.1115/ES2016-59630.

This paper presents qualitative evidence to support the application of microwave induced plasma gasification (MIPG) technology for converting municipal solid wastes (MSW) to syngas and to use it for enhanced oil recovery (EOR). The target for the case study of this paper is the United Arab Emirates, which is a major producer and exporter of petroleum. The main EOR method employed by the UAE’s oil companies is the miscible gas flooding method, whereby natural gas or carbon dioxide is injected into the oil reservoirs to boost the oil pressure, reduce the viscosity of the oil and to increase the pumping rates. UAE purchases natural gas for power production and EOR from its neighbor, Qatar, which makes the UAE a net importer of natural gas and a major consumer of energy, while reducing the national income from the oil sales. The UAE is looking at ways to boost its oil production and to reduce the usage of natural gas, including the injection of carbon dioxide, nitrogen and steam generated by concentrated solar power.

UAE and the other Arabian Gulf nations have some of the highest per capita rates of production of domestic waste. Landfilling is the prevalent form of waste disposal for industrial, commercial and residential waste. Incineration-type waste-to-energy power plants are being constructed, but they are not the most effective solution due to cost and environmental reasons.

This paper proposes a solution that covers the two problems with one technology, namely MIPG of MSW. MIPG is shown to be the most efficient method of gasification available, as it uses much less energy for producing and sustaining the plasma than other techniques, and produces a much cleaner syngas than thermochemical gasification schemes. The syngas can be used for electricity generation or for making fuels and raw materials in the Fischer-Tropsch or similar processes. In this proposal, MIPG will be used to turn MSW, sewage sludge and biomass wastes into syngas. A part of the syngas will be used to produce electricity to power the petroleum extraction processes, while the carbon dioxide formed in this combustion of syngas can be captured and used for EOR in deep oil wells, which also functions as a form of sequestration of carbon. In addition, syngas can be turned into methane and synthetic natural gas using the Fischer-Tropsch or Sabatier process and then pumped into the oil wells. Some of the petroleum extracted can also be gasified using the MIPG method for the production of synthetic natural gas. Thus, the dependence on natural gas imports will be eliminated, while also achieving zero landfill targets.

Commentary by Dr. Valentin Fuster
2016;():V001T02A011. doi:10.1115/ES2016-59632.

This review paper describes techniques proposed for applying microwave-induced plasma gasification (MIPG) for cleaning rivers, lakes and oceans of synthetic and organic waste pollutants by converting the waste materials into energy and useful raw materials.

Rivers close to urban centers tend to get filled with man-made waste materials, such as plastics and paper, gradually forming floating masses that further trap biological materials and animals. In addition, sewage from residences and industries, as well as rainwater runoff pour into rivers and lakes carrying solid wastes into the water bodies. As a result, the water surfaces get covered with a stagnant, thick layer of synthetic and biological refuse which kill the fish, harm animals and birds, and breed disease-carrying vectors. Such destruction of water bodies is especially common in developing countries which lack the technology or the means to clean up the rivers.

A terrible consequence of plastic and synthetic waste being dumped irresponsibly into the oceans is the presence of several large floating masses of garbage in the worlds’ oceans, formed by the action of gyres, or circulating ocean currents. In the Pacific Ocean, there are numerous debris fields that have been labeled the Great Pacific Garbage Patch. These patches contain whole plastic litters as well as smaller pieces of plastic, called microplastics, which are tiny fragments that were broken down by the action of waves. These waste products are ingested by animals, birds and fishes, causing death or harm. Some of the waste get washed ashore on beaches along with dead marine life.

The best solution for eliminating all of the above waste management problems is by the application of MIPG systems to convert solid waste materials and contaminated water into syngas, organic fuels and raw materials. MIPG is the most efficient form of plasma gasification, which is able to process the most widest range of waste materials, while consuming only about a quarter of the energy released from the feedstock. MIPG systems can be scaled in size, power rating and waste-treatment capacity to match financial needs and waste processing requirements. MIPG systems can be set up in urban locations and on the shores of the waterbody, to filter and remove debris and contaminants and clean the water, while generating electric power to feed into the grid, and fuel or raw materials for industrial use.

For eliminating the pelagic debris fields, the proposed design is to have ships fitted with waste collector and filtration systems that feeds the collected waste materials into a MIPG reactor, which converts the carbonaceous materials into syngas (H2 + CO). Some of the syngas made will be used to produce the electric power needed for running the plasma generator and onboard systems, while the remainder can be converted into methanol and other useful products through the Fischer-Tropsch process. This paper qualitatively describes the implementation schemes for the above processes, wherein MIPG technology will be used to clean up major waste problems affecting the earth’s water bodies and to convert the waste into energy and raw materials in a sustainable and environmentally friendly manner, while reducing the dependence on fossil fuels and the release of carbon dioxide and methane into the atmosphere.

Commentary by Dr. Valentin Fuster

CHP and Hybrid Power and Energy Systems

2016;():V001T03A001. doi:10.1115/ES2016-59117.

Small scale Distributed Generation with waste heat recovery (<50 kW power output, micro-DG/CHP) is an expanding market supporting the widespread deployment of on-site generation to much larger numbers of facilities. The benefits of increased overall thermal efficiency, reduced pollutant emissions, and grid/microgrid support provided by DG/CHP can be maximized with greater quantities of smaller systems that better match the electric and thermal on-site loads. The 3-year CEC funded program to develop a natural gas fueled automotive based rotary engine for micro-DG/CHP, capitalizing upon the unique attributes engine configuration will be presented including initial performance results and plans for the balance of the program.

Commentary by Dr. Valentin Fuster
2016;():V001T03A002. doi:10.1115/ES2016-59118.

One of the primary challenges facing DG/CHP systems involves effective design and operational match with potential end applications. A key weakness in the deployment of many DG/CHP systems is the inability of the installed system to properly match up with the actual load that it is being asked to serve. In general, it is difficult to optimally match the demand of both electricity and thermal requirements with a single system as a result of variations in loads with season, site operational changes, and other factors. It seems apparent that improved flexibility in how a DG/CHP system’s electricity/thermal production ratio is established will provide more flexibility in how a given system can meet a given demand profile. While examples of temperature increase via supplemental burners are available for small scale systems, a system to control both exhaust temperature (increase and decrease) and overall flow rate is not available. This paper describes the results of a multi-year program sponsored by the California Energy Commission to develop and demonstrate an exhaust energy tailoring system that will provide flexibility in both temperature adjustments and overall exhaust flow to meet the requirements of various heat recovery systems while providing low emission when coupled with a commercial distributed generation “prime mover”. The program integrated a multi-stage Rich/Quick-mix/Lean combustion system operating on the vitiated exhaust stream from a Capstone Model “iCHP65” to provide flexible wide range control of the exhaust energy and quality. Additionally, the integrated system reduced both the criteria pollutant concentration levels and emission rates over the Capstone unit alone. This paper describes the development of the unique vitiated air combustor system as well as full scale test results.

Commentary by Dr. Valentin Fuster
2016;():V001T03A003. doi:10.1115/ES2016-59172.

Micro-combined heat and power (MCHP) systems generate heat and electricity concurrently, making them an ideal addition for home and small/medium business owners to generate their own electricity and replace conventional natural gas-burning boilers. Combining MCHP units with thermal and electric storage systems can aid in decoupling supply and demand of energy. In such a combined setup, MCHP units can run for prolonged periods when they not only cover existing demand but charge storage systems for deferred consumption of energy. In the present work, we analyzed such an MCHP system, with a particular focus on integrating electrical storage systems and the resulting degree of electrical self-sufficiency achievable under realistic working conditions. We implemented a system control logic to optimize MCHP unit run time geared towards taking energy storage system charging levels into account. We demonstrate that an MCHP unit and electrical storage system can complement each other benefitting overall system performance. Separating days according to their respective degree of electrical self-sufficiency enabled us to identify supply composition characteristics that result in higher electrical load coverage by MCHP-generated electricity.

Commentary by Dr. Valentin Fuster
2016;():V001T03A004. doi:10.1115/ES2016-59355.

Nuclear reactor systems present a promising sustainable energy source for the future. Simply, a nuclear reactor heats a coolant that powers a turbine to create electricity. The coolant then can either be re-cooled or can be used for process heat applications. By utilizing the heat off the reactor less energy is wasted. A few of the proposed uses of the wasted heat are water desalination, hydrogen production, or pyrolysis. Nuclear power plants most often provide baseload power and are very inflexible. One way to address this is to use nuclear hybrid energy systems.

The goal of this research is to create a system that mimics the waste heat from a reactor, demonstrates how to utilize that heat, and shows that when energy demand is low the reactor does not need to reduce power; the energy can be directed elsewhere to create goods. We have developed an Energy Conversion Loop to act as a testbed for experimentation of the aforementioned processes and test the possibility of nuclear hybrid energy systems.

The current design consists of a series of heat exchangers that transfer heat between hot air 427 °C (800 °F) and room temperature water. Each loop of the system mimics a type of process that can be tested with a waste heat application. Early models show the system is capable of producing air temperatures near 427 °C (800 °F) and steam temperatures of 154.4 °C (310 °F). These temperatures match needed process heat temperatures for pyrolysis, multi-effect distillation, and multi-stage flash distillation and can be used to simulate other processes for lab scale testing of wasted process heat. Physical testing will be completed in the future to confirm these results.

Commentary by Dr. Valentin Fuster
2016;():V001T03A005. doi:10.1115/ES2016-59452.

Small Modular Reactor (SMR) technologies have been recently deemed by the DOE as clean energy, a low carbon-dioxide emitting “alternative energy” source. Recent UN Sustainability Goals and Global Climate Talks to reduce the anthropomorphic Carbon-Dioxide atmospheric concentrations signal a renewed interest and need for nuclear power. The objective of this paper is to present an improved approach to the evaluation of “Hybrid Nuclear Energy Systems”. A hybrid energy system is defined as an energy system that utilizes two or more sources of energy to be used in single or multiple applications. Traditional single sourced energy or power systems require the amount of energy creation and the production of usable power to be carefully balanced. With the introduction of multiple energy sources, loads, and energy capacitors, the design, simulation, and operation of such hybrid systems requires a new approach to analysis and control. This paper introduces three examples of “Hybrid Nuclear Energy Systems”, for large scale power, industrial heat, and electricity generation. The system component independence, reliability, availability, and dynamic control aspects, coupled with component operational decisions presents a new way to optimize energy production and availability. Additional novel hybrid hydro-nuclear systems, concentrated solar-nuclear power desalination systems, and nuclear-insitu petroleum extraction systems are compared. The design aspects of such hybrid systems suitable for process heat, electricity generation, and/or desalination applications are discussed. After a multiple-year research study of past hybrid reactor designs and recent system proposals, the following design evaluation approach is the result of analysis of the best concepts discovered.

This review of existing literature has summerized that postulated benefits of Hybrid Nuclear Sytems are; reduced greenhouse gas emissions, increased energy conversion efficiency, high reliability of electricity supply and consistent power quality, reduced fossil fuel dependence, less fresh water consumption, conversion of local coal or shale into higher value fuels, while lowering the risks and costs.

As these proposed hybrid systems are interdisciplinary in nature, they will require a new multidisciplinary approach to systems evaluation.

Topics: Nuclear power
Commentary by Dr. Valentin Fuster
2016;():V001T03A006. doi:10.1115/ES2016-59471.

As variable generation electricity sources, namely wind and solar, increase market penetration, the variability in the value of electricity by time of day has increased dramatically. In response to increase in electricity demand, natural gas “peaker plants” are being added to the grid, and the need for spinning and nonspinning reserves have increased. Many natural gas, and other heat source based, power plants exist as combined heat and power (CHP), or cogeneration, plants. When built for industrial use, these plants are sized and run based on heat needs of an industrial facility, and are not optimized for the value of electricity generated. With the inclusion of new, less expensive thermal energy storage (TES) systems, the heating and electricity usage can be separated and the system can be optimized separately. The use of thermal energy storage with CHP improves system economics by improving efficiency, reducing upfront capital expenditures, and reducing system wear.

This paper examines the addition of thermal energy storage to industrial natural gas combined heat and power (CHP) plants. Here a case study is presented for a recycled paper mill near Los Angeles, CA. By implementing thermal energy storage, the mill could decouple electric and heat production. The mill could take advantage of time-of-day pricing while producing the constant heat required for paper processing. This paper focuses on plant economics in 2012 and 2015, and suggests that topping cycle industrial CHP plants could benefit from the addition of high temperature (400–550°C) energy storage. Even without accounting for the California incentives associated with implementing advanced energy storage technologies and distributed generation, the addition of energy storage to CHP plants can drastically reduce the payback period below the 25 year expected economic lifetime of a plant. Thus thermal energy storage can make more CHP plants economically viable to build.

Commentary by Dr. Valentin Fuster
2016;():V001T03A007. doi:10.1115/ES2016-59517.

Integration of non-dispatchable renewable energy sources such as wind and solar into the grid is challenging due to the stochastic nature of energy sources. Hence, electrical hubs (EH) and virtual power plants that combine non-dispatchable energy sources, energy storage and dispatchable energy sources such as internal combustion generators and micro gas turbines are getting popular. However, designing such energy systems considering the electricity demand of a neighborhood, curtailments for grid interactions and real time pricing (RTP) of the main utility grid (MUG) is a difficult exercise. Seasonal and hourly variation of electricity demand, potential for each non-dispatchable energy source and RTP of MUG needs to be considered when designing the energy system. Representation of dispatch strategy plays a major role in this process where simultaneous optimization of system design and dispatch strategy is required. This study presents a bi-level dispatch strategy based on reinforced learning for simultaneous optimization of system design and operation strategy of an EH. Artificial Neural Network (ANN) was combined with a finite state controller to obtain the operating state of the system. Pareto optimization is conducted considering, lifecycle cost and system autonomy to obtain optimum system design using evolutionary algorithm.

Commentary by Dr. Valentin Fuster
2016;():V001T03A008. doi:10.1115/ES2016-59518.

The importance of integrating renewable energy sources into standalone energy systems is highlighted in recent literature. Maintaining energy efficiency is challenging in designing such hybrid energy systems (HES) due to seasonal variation of renewable energy potential. This study evaluates the limitations in minimizing the losses in renewable energy generated mainly due to energy storage limitations and minimizing fuel consumption of the internal combustion generator (ICG). A standalone hybrid energy system with Solar PV (SPV), wind, battery bank and an ICG is modeled and optimized in this work. Levelized Energy Cost (LEC), Waste of Renewable Energy (WRE) and Fuel Consumption (FC) are taken as objective functions. Results highlight the importance of considering WRE as an objective function which increase the mix of energy sources that can help to increase the reliability of the system.

Commentary by Dr. Valentin Fuster

Concentrating Solar Power

2016;():V001T04A001. doi:10.1115/ES2016-59015.

Concentrated Solar Power using supercritical CO2 (S-CO2) Brayton cycles offers advantages of similar and even higher overall thermal efficiencies compared to conventional Rankine cycles using superheated or supercritical steam. In this paper, a S-CO2 Recompression Brayton cycle is integrated with a central receiver. The effect of pressure drops in heat exchangers and solar receiver surface temperature on the thermal and ex-ergetic performance of the recompression Brayton cycle with and without reheat condition is studied. Energy, exergy and mass balance are carried out for each component and first law and exergy destruction are calculated. In order to obtain optimal operating condition, optimum cycle pressure ratios are obtained by maximising the thermal efficiency. The results showed that under low solar receiver pressure drops and solar receiver temperature approach, the S-CO2 Recompression Brayton cycle has more thermal and exergy efficiencies than the no reheat case. Pressure drop reduces the gap between reheat and no reheat case, and for pressure drops in the solar receiver of 2.5% or higher, reheat has significant impact on thermal and exergy performance of the cycle studied. The overall exergy efficiency showed a bell shaped, reaching a maximum value between 19.5–22.5% at turbine inlet temperatures in the range of 660–755 °C for solar receiver surface temperature approach among 100–200 °C.

Commentary by Dr. Valentin Fuster
2016;():V001T04A002. doi:10.1115/ES2016-59019.

A previously developed control scheme for thermal energy storage systems was coded and integrated into a previously developed annual performance model of Shams I to evaluate the consequences of incorporating a 2 GWhth capacity thermal energy storage system into the operation of the 100 MWe concentrated solar power plant. The existing solar field of Shams I was doubled in size to accommodate the proposed thermal energy storage system augmentation resulting in 157 GWhth of extra heat sent directly to the power block as well as 564 GWhth of residual heat sent to the thermal energy storage system for later use. Gross power generation was increased from 337 to 671 GWhe. The overall outcome of integrating the proposed thermal energy storage system into Shams I and applying its developed control scheme is increased and more streamlined supply of electricity in addition to reduced idle time. Despite integrating a 2 GWhth capacity thermal energy storage system into the operation of Shams I, model results showed that a non-stop 24-hour operation running at full load was difficult to achieve. In order to attain a non-stop operation, the size of the thermal energy storage must be increased or night time generation should be decreased.

Commentary by Dr. Valentin Fuster
2016;():V001T04A003. doi:10.1115/ES2016-59046.

Highly-specular reflective surfaces that can withstand elevated-temperatures are desirable for many applications including reflective heat shielding in solar receivers and secondary reflectors, which can be used between primary concentrators and heat collectors. A high-efficiency, high-temperature solar receiver design based on arrays of cavities needs a highly-specular reflective surface on its front section to help sunlight penetrate into the absorber tubes for effective flux spreading. Since this application is for high-temperature solar receivers, this surface needs to be durable and to maintain its optical properties through the usable life. Degradation mechanisms associated with elevated temperatures and thermal cycling, which include cracking, delamination, corrosion/oxidation, and environmental effects, could cause the optical properties of surfaces to degrade rapidly in these conditions. Protected mirror surfaces for these applications have been tested by depositing a thin layer of SiO2 on top of electrodeposited silver by means of the sol-gel method. To obtain an effective thin film structure, this sol-gel procedure has been investigated extensively by varying process parameters that affect film porosity and thickness. Endurance tests have been performed in a furnace at 150°C for thousands of hours. This paper presents the sol-gel process for intermediate-temperature specular reflective coatings and provides the long-term reliability test results of sol-gel protected silver-coated surfaces.

Commentary by Dr. Valentin Fuster
2016;():V001T04A004. doi:10.1115/ES2016-59051.

The present study introduces fundamental aspects of a novel concentrated photovoltaics (CPV) technology. The technology is based on combining CPV/T receiver along with a solar thermal receiver. The combination is referred to as a High Concentrated Photovoltaic/Thermal - Combined receiver or HCPV/T-CT. The receiver is allocated in lieu of the conventional solar thermal receivers in the solar tower power plant schemes. The plant is designed to generate electricity and thermal energy simultaneously prior to integration with the conventional water desalination plant. The centralized generation in the CPV/T-CT receiver will remarkably simplify the complexity of the conventional solar power plants, and eliminate the piping networks’ energy losses in the CPV/T Dish tracking plants. The viability of the HCPV/T-CT power tower plant has also been investigated by; firstly, designing and simulating the plant performance using the System advisor model (SAM) software, and secondly, designing a prototype receiver and then deriving a mathematical model. The Levelised Cost Of Electricity/Energy (LCOE) was found to be 0.119 $/kWhe and 0.021 $/kWhe for electricity and energy generation, respectively, while the photovoltaic cells temperature maintained below the 90 °C.

Commentary by Dr. Valentin Fuster
2016;():V001T04A005. doi:10.1115/ES2016-59158.

Multiple receiver designs have been evaluated for improved optics and efficiency gains including flat panel, vertical-finned flat panel, horizontal-finned flat panel, and radially finned. Ray tracing using SolTrace was performed to understand the light-trapping effects of the finned receivers. Re-reflections of the fins to other fins on the receiver were captured to give an overall effective solar absorptance.

The ray tracing, finite element analysis, and previous computational fluid dynamics showed that the horizontal-finned flat panel produced the most efficient receiver with increased light-trapping and lower overall heat loss. The effective solar absorptance was shown to increase from an intrinsic absorptance of 0.86 to 0.96 with ray trace models. The predicted thermal efficiency was shown in CFD models to be over 95%. The horizontal panels produce a re-circulating hot zone between the panel fins reducing convective loss resulting in a more efficient receiver. The analysis and design of these panels are described with additional engineering details on testing a flat panel receiver and the horizontal-finned receiver at the National Solar Thermal Test Facility. Design considerations include the structure for receiver testing, tube sizing, surrounding heat shielding, and machinery for cooling the receiver tubes.

Topics: Design , Modeling
Commentary by Dr. Valentin Fuster
2016;():V001T04A006. doi:10.1115/ES2016-59238.

This paper evaluates the on-sun performance of a 1 MW falling particle receiver. Two particle receiver designs were investigated: obstructed flow particle receiver vs. free-falling particle receiver. The intent of the tests was to investigate the impact of particle mass flow rate, irradiance, and particle temperature on the particle temperature rise and thermal efficiency of the receiver for each design. Results indicate that the obstructed flow design increased the residence time of the particles in the concentrated flux, thereby increasing the particle temperature and thermal efficiency for a given mass flow rate. The obstructions, a staggered array of chevron-shaped mesh structures, also provided more stability to the falling particles, which were prone to instabilities caused by convective currents in the free-fall design. Challenges encountered during the tests included non-uniform mass flow rates, wind impacts, and oxidation/deterioration of the mesh structures. Alternative materials, designs, and methods are presented to overcome these challenges.

Commentary by Dr. Valentin Fuster
2016;():V001T04A007. doi:10.1115/ES2016-59252.

Previous successful tests and promising results of a Centrifugal Particle Receiver (CentRec) for high temperature solar applications has been achieved in a lab scale prototype with 7.5 kWth [1, 2, 3]. In a next step this receiver technology is scaled up to higher thermal power for a future pilot plant.

This paper presents the optimization methodology of the design and technical solutions. It describes the manufacturing and assembly of the prototype and first tests and results of the commissioning including cold particle tests and prototype costs. Finally the paper gives an outlook on the planned further steps regarding hot lab tests and solar tests.

Commentary by Dr. Valentin Fuster
2016;():V001T04A008. doi:10.1115/ES2016-59258.

The increasing demand for renewable energy sources necessitates the development of more efficient technologies. Concentrated solar power (CSP) towers exhibit promising qualities, as temperatures greater than 1000°C are possible. The heat transfer fluid implemented to capture the sun’s energy significantly impacts the overall performance of a CSP system. Current fluids, such as molten nitrate salts and steam, have limitations; molten salts are limited by their small operational temperature range while steam requires high pressures and is unable to act as an effective storage medium. As a result, a new heat transfer fluid composed of ceramic particles is being investigated, as ceramic particles demonstrate no practical limit on operation temperature and have the ability to act as a storage medium. This study sought to further investigate the use of dense granular flows as a new heat transfer fluid. Previous work validated the use of such flows as a heat transfer fluid; the present work examined the effect of flow rate, as well as the particle size and type on the heat transfer to the particle fluid. Three different types of particles were tested, along with two different diameter particles. Of the three materials tested, the particle type did not appear to effect the heat transfer. Particle diameter, however, did effect the heat transfer, as a smaller diameter particle yielded slightly higher heat transfer to the fluid. Flow rates ranging from 30 to 200 kg/m2-s were tested. Initially, the heat transfer to the flow, characterized by the convective heat transfer coefficient, decreased with increasing flow rate. However, at approximately 80 kg/m2-s, the heat transfer coefficient began to increase with increasing flow rate. These results indicate that a dense granular flow consisting of small diameter particles and traveling at very slow or fast flow rates yields the best wall to “fluid” heat transfer.

Commentary by Dr. Valentin Fuster
2016;():V001T04A009. doi:10.1115/ES2016-59268.

The design and building of two thermal energy storage (TES) pilot plants to be used for concentrated solar power (CSP) applications is explained and compared. Both pilot plants are based on a two-tank molten salt storage technology (composed by a hot and a cold tank) which works under a TES process. This process has three main steps: charge, storage and discharge. Charging and discharging cannot be performed simultaneously, and the whole process is considered to be cyclic: (1) during the charging process, the heat transfer fluid (HTF) is heated up with the solar collectors from the solar field up to a temperature of 393 °C. Then, the HTF exchanges its energy with the molten salts at the heat exchanger. During this process, the molten salts flow from the cold tank through the heat exchanger, arriving at the hot tank at a temperature up to 388 °C. (2) During the storage, the molten salts are stored in the hot tank at a temperature up to 388 °C. (3) Finally, during the discharging process, which corresponds to the period when no more solar radiation is available, the energy stored in the hot tank is used to produce electricity. Molten salts flow from the hot tank through the heat exchanger to the cold tank, heating up the HTF. This HTF carries the thermal energy to the power block, where it is converted to electricity. The first pilot plant presented in this study was designed and built by Abengoa in 2008 in Seville (Spain). It consisted of an 8.1 MWhth facility which contained all the components (successfully tested and optimized) that were lately used in commercial CSP plants. The second pilot plant consisted of a 0.3 MWhth facility designed, built and tested in 2008 at the University of Lleida (Spain) in conjunction with Abengoa. The TES material used in both pilot plants was a mixture of sodium nitrate and potassium nitrate (60% NaNO3 and 40% KNO3). The main differences between the two facilities fall on the size and on the operating mode: while the facility in Seville is charged with solar energy and discharged against a power cycle, the facility in Lleida is charged with an electrical boiler and discharged against a HTF-air heat exchanger. This paper presents the main components of both facilities and the lessons learnt during operation at pilot plant scale, which have been found to be useful to guarantee the correct start-up and operation of new commercial CSP plants built worldwide. These lessons learnt include key aspects like filling up the storage tanks, heat tracing systems and equipment used.

Topics: Design , Testing , Storage
Commentary by Dr. Valentin Fuster
2016;():V001T04A010. doi:10.1115/ES2016-59298.

Arguably, the most complicated and problematic mathematical formulation for solar collectors belongs to the heliostat field collectors. Consequently, extensive researches are carried out in order to develop several codes capable of providing heliostat field analysis and optimization. Noting that most of the aforementioned heliostat field codes are developed based on the radial-staggered field layout which is arguably the most popular and widely implemented heliostat field configuration in the literature. Nevertheless, a ground-breaking heliostat field layout based on the spiral patterns of phyllotaxis discs is recently proposed. It was argued that the transition between the areas with high and low heliostat field density is not continuous in radial-staggered configuration. In a study by the authors, the spiral and radial-staggered field layouts thermo-economic analyses are compared and the results points to the superiority of the radial-staggered layout. Nevertheless, it is believed that utilizing two design variables might be only sufficient for small number of mirrors. Therefore, more design variables must be implemented to fully control different areas of the field for larger capacity heliostat fields. In this paper, spiral field zoning is proposed and its impact on the spiral heliostat field layout performance is assessed. By dividing the heliostat field into multiple zones, each zone is designed with a set of design variables (two design variables: a and b). Consequently, the impacts heliostat field zoning might have on the field thermo-economic performance are investigated.

Topics: Thermoeconomics
Commentary by Dr. Valentin Fuster
2016;():V001T04A011. doi:10.1115/ES2016-59409.

Flux distributions from solar field collectors are typically evaluated using a beam characterization system, which consists of a digital camera with neutral density filters, flux gauge or calorimeter, and water-cooled Lambertian target panel. The pixels in camera image of the flux distribution are scaled by the flux peak value measured with the flux gauge or the total power value measured with the calorimeter. An alternative method, called PHLUX developed at Sandia National Laboratories, can serve the same purpose using a digital camera but without auxiliary instrumentation. The only additional information required besides the digital images recorded from the camera are the direct normal irradiance, an image of the sun using the same camera, and the reflectivity of the receiver or target panel surface.

The PHLUX method was evaluated using two digital cameras (Nikon D90 and D3300) at different flux levels on a target panel. The performances of the two cameras were compared to each other and to measurements from a Kendall radiometer. For consistency in comparison of the two cameras, the same focal length lenses and same number of neutral density filters were used. Other camera settings (e.g., shutter speed, f-stop, etc.) were set based on the aperture size and performance of the cameras. The Nikon D3300 has twice the number of pixels as the D90. D3300 provided higher resolution, however, due to the smaller pixel sizes the images were noisier, and the D90 with larger pixels had better response to low light levels. The noise in the D3300, if not corrected, could result in gross overestimation of the irradiance calculations. After corrections to the D3300 flux images, the PHLUX results from the two cameras showed they agreed to within 8% for a peak flux level of 1000 suns on the target, and less than 10% error in the peak flux when compared to the Kendall radiometer.

Commentary by Dr. Valentin Fuster
2016;():V001T04A012. doi:10.1115/ES2016-59463.

Direct solar power receivers consist of tubular arrays, or panels, which are typically tubes arranged side by side and connected to an inlet and outlet manifold. The tubes absorb the heat incident on the surface and transfer it to the fluid contained inside them. To increase the solar absorptance, high temperature black paint or a solar selective coating is applied to the surface of the tubes. However, current solar selective coatings degrade over the lifetime of the receiver and must be reapplied, which reduces the receiver thermal efficiency and increases the maintenance costs. This work presents an evaluation of several novel receiver shapes which have been denominated as fractal like geometries (FLGs). The FLGs are geometries that create a light-trapping effect, thus, increasing the effective solar absorptance and potentially increasing the thermal efficiency of the receiver. Five FLG prototypes were fabricated out of Inconel 718 and tested in Sandia’s solar furnace at two irradiance levels of ∼15 and 30 W/cm2 and two fluid flow rates. Photographic methods were used to capture the irradiance distribution on the receiver surfaces and compared to results from ray-tracing models. This methods provided the irradiance distribution and the thermal input on the FLGs. Air at nearly atmospheric pressure was used as heat transfer fluid. The air inlet and outlet temperatures were recorded, using a data acquisition system, until steady state was achieved. Computational fluid dynamics (CFD) models, using the Discrete Ordinates (DO) radiation and the k-ω Shear Stress Transport (SST) equations, were developed and calibrated, using the test data, to predict the performance of the five FLGs at different air flow rates and irradiance levels. The results showed that relative to a flat plate (base case), the new FLGs exhibited an increase in the effective solar absorptance from 0.86 to 0.92 for an intrinsic material absorptance of 0.86. Peak surface temperatures of ∼1000°C and maximum air temperature increases of ∼200°C were observed. Compared to the base case, the new FLGs showed a clear air outlet temperature increase. Thermal efficiency increases of ∼15%, with respect to the base case, were observed. Several tests, in different days, were performed to assess the repeatability of the results. The results obtained, so far, are very encouraging and display a very strong potential for incorporation in future solar power receivers.

Topics: Solar energy
Commentary by Dr. Valentin Fuster
2016;():V001T04A013. doi:10.1115/ES2016-59465.

The Combustion and Solar Energy Laboratory (C&SEL) at San Diego State University is developing a Small Particle Heat Exchange Receiver (SPHER) to absorb and transfer heat from concentrated solar radiation to a working fluid for a gas turbine. The SPHER is to be used with a Concentrated Solar Power (CSP) system where a heliostat field highly concentrates solar radiation on the optical aperture of the SPHER. The solar radiation is volumetrically absorbed by a unique carbon nanoparticle gas mixture within the cavity of the SPHER. This research focuses on comparing a Computational Fluid Dynamics (CFD) model using the ANSYS FLUENT Discrete Ordinates (DO) Model and a program developed by the C&SEL which uses a Monte Carlo Ray Trace (MCRT) method to calculate the spatial and directional distribution of radiation for an idealized solar receiver geometry.

Previous research at the C&SEL has shown successful implementation of the MCRT method to calculate the spatial and directional distribution of radiation for an idealized solar receiver geometry. The MCRT method is highly accurate and will serve as the benchmark solution for this research. However the MCRT code takes several days to run, is inflexible to geometry changes, and is cumbersome to implement as the MCRT code needs to be rewritten for each new receiver geometry being considered. These factors necessitate the need to find an alternate method that accurately calculates the spatial and directional distribution of radiation for a solar receiver and can be efficiently implemented for various receiver geometries being studied.

The Discrete Ordinates method is a new method for solving the Radiative Transport Equations (RTE) using a FORTRAN program, developed by the C&SEL, and the ANSYS FLUENT Discrete Ordinates model for calculating the RTE. The FORTRAN program calculates the proper inlet radiation boundary conditions that ANSYS FLUENT uses for calculating the RTE. The methodology used for determining the correct CFD mesh, radiative boundary conditions, optimal number of DO theta and phi discretization, as well as the optical properties of the working fluid will be presented in this paper.

The main focus of this research is to compare two different methods for solving the Radiative Transport Equations within the idealized SPHER. The solution data for several cases using the previous coupled MCRT method and the ANSYS FLUENT Discrete Ordinates method is presented for both a collimated and diffuse gray radiation approximation. The case studies focus on researching how the MCRT method and Discrete Ordinates method differ when comparing critical receiver parameters such as the mean outlet temperature, wall temperature profile, outlet tube temperature profile, and total receiver efficiency while keeping the total inlet radiation flux of 5 MW and inlet mass flow rate of 5 kg/s constant. This research also presents a study on the optimal Discrete Ordinates angular discretization, as well as a study to determine the solution’s dependence on the number of inlet boundary conditions imposed on the window.

Commentary by Dr. Valentin Fuster
2016;():V001T04A014. doi:10.1115/ES2016-59491.

With the shortage of fossil fuels and its negative effects on the environment, solar energy as one type of renewable energy has attracted increasing attention both socially and politically. There are two approached to use solar energy for generating electricity, i.e., using solar energy to directly to make work or integrating solar energy into fossil-fueled plant. The solar-aided coal-fired power generation (SACPG) mechanism is proven an effective way to use solar energy efficiently. In this paper, SACPG system and solar-alone parabolic trough CSP plant are modelled respectively. A comparison discussion related to TES system between SACPG system and solar-alone CSP plant is presented. The aim is to find what role of TES system will play in these two different systems.

Through analysis, the role TES system plays varies in solar-alone power generation system and SACPG system. For solar-alone power generation system, the main function for TES system lies in storing surplus solar heat. Besides, there exists an optimum loop number with highest annual SEE with a specific TES hour. However, TES system for SACPG system not only stores the surplus solar heat, but also adjusts working condition. With the help of TES system, the working condition could be set as the high-pressure extraction steam could be totally replaced by solar heat. By doing so, annual solar power generation and annual SEE could be improved compared with that without TES system.

Commentary by Dr. Valentin Fuster
2016;():V001T04A015. doi:10.1115/ES2016-59516.

The process of generating electricity using solar energy took a great interest in the recent period for its contribution to the reduction of the fossil fuel consumption and the harmful emissions to the environment. The main task of this article is to simulate the thermal performance of a solar power plant for electricity production using a parabolic trough concentrator for accumulating the solar heat. The plant includes a stratified storage tank, steam generator, steam turbine and an electric generator. The simulation studies the effect of the design parameters of the solar field and the storage tank on the annual performance of a 1 MWe solar electric power plant. The simulation platform TRNSYS was used to model the solar power plant including the solar concentrator field, the storage tank, and the steam generator. The simulation predicts the instantaneous and annual heat energy collected by the solar concentrator and the heat energy rate supplied, extracted, and stored in the storage tank. It predicts also the rate and the quality of the steam produced. This analysis was applied to four sites in Egypt to study the effect of the solar radiation on the energy produced in those sites.

Commentary by Dr. Valentin Fuster
2016;():V001T04A016. doi:10.1115/ES2016-59544.

This paper evaluates novel particle release patterns for high-temperature falling particle receivers. Spatial release patterns resembling triangular and square waves are investigated and compared to the conventional straight-line particle release. A design of experiments was developed, and a simulation matrix was developed that investigated three two-level factors: amplitude, wavelength, and wave type. Results show that the wave-like patterns increased both the particle temperature rise and thermal efficiency of the receiver relative to the straight-line particle release. Larger amplitudes and smaller wavelengths increased the performance by creating a volumetric heating effect that increased light absorption and reduced heat loss. Experiments are also being designed to investigate the hydraulic and thermal performance of these new particle release configurations.

Commentary by Dr. Valentin Fuster
2016;():V001T04A017. doi:10.1115/ES2016-59607.

The high-temperature particle – supercritical carbon dioxide (sCO2) Brayton power system is a promising option for concentrating solar power (CSP) plants to achieve SunShot metrics for high-temperature operation, efficiency, and cost. This system includes a falling particle receiver to collect solar thermal radiation, a dry-cooled sCO2 Brayton power block to produce electricity, and a particle to sCO2 heat exchanger to couple the previous two. While both falling particle receivers and sCO2 Brayton cycles have been demonstrated previously, a high temperature, high pressure particle/sCO2 heat exchanger has never before been demonstrated. Industry experience with similar heat exchangers is limited to lower pressures, lower temperatures, or alternative fluids such as steam. Sandia is partnering with three experienced heat exchanger manufacturers to develop and down-select several designs for the unit that achieves both high performance and low specific cost to retire risks associated with a solar thermal particle/sCO2 power system. This paper describes plans for the construction of a particle sCO2 heat exchanger testbed at Sandia operating above 700 °C and 20 MPa, with the ability to couple directly with a previously-developed falling particle receiver for on-sun testing at the National Solar Thermal Test Facility (NSTTF).

Commentary by Dr. Valentin Fuster
2016;():V001T04A018. doi:10.1115/ES2016-59615.

Supercritical Carbon Dioxide (sCO2) power cycles have the potential to deliver high efficiency at low cost. However, in order for s-CO2 cycle to reach high efficiency, highly effective recuperators are needed. These recuperative heat exchangers must transfer heat at a rate that is substantially larger than the heat transfer to the cycle itself and can therefore represent up to 24% of the total power block cost in a recompression Brayton cycle [1]. Lower cost regenerators are proposed as a cost saving alternative to high cost printed circuit recuperators. A regenerator is a heat exchanger that alternately has hot and cold fluid passing through it. During the first half of its cycle the hot gas is passed over a storage media bed (stainless steel balls, screens, or similar fill material) where thermal energy is stored. During the next half of the cycle, cold fluid is passed through in the opposite direction, extracting the thermal energy from the bed. By operating a cycle with two (or more) regenerators, where one is always in a hot to cold (HTC) blow and the other in a cold to hot blow (CTH), a quasi-steady state can be achieved in the cycle to allow continuous operation. A model of the regenerator was created and used in place of a recuperator in a model of a 10MW power plant. The thermal effectiveness of the regenerator cycle was slightly lower than the recuperator cycle, however the regenerator cycle had a saving of about 9.3 percent in the Levelized Cost of Energy (LCoE). A scale model of the regenerator is under construction which will verify the performance of the regenerator model.

Commentary by Dr. Valentin Fuster
2016;():V001T04A019. doi:10.1115/ES2016-59618.

Here we describe a new type of point-focus solar collector for CSP called “track and tilt”. It bridges the gap between dish and heliostat arrays collectors, having the high optical efficiency of a dish but with larger aperture (> 1000 m2) focused to a tower mounted receiver in fixed gravity orientation. It is well matched to the next generation of high efficiency cavity receivers transferring heat to a storage medium at temperatures exceeding 700C.

The collector uses silvered glass reflectors mounted on a rotating, rigid structure in the form of a 120 degree conical arc. In operation, this large structure rotates in azimuth on a track around the central receiver tower, keeping the gravity load on the structure constant. The central receiver is rotated about a vertical axis so as to face the reflector arc. The reflectors are concave, all with the same focal length, and are individually tilted to follow solar elevation to focus sunlight onto the tower-mounted receiver.

A detailed optical model made of a collector with 40 m focal length has 1,450 m2 total reflector area, and delivers on average 1.2MW of sunlight to the receiver, (under 1000 W/m2 DNI and allowing for reflector and small geometric losses). The collector forms an only slightly aberrated image of the sun at the receiver, showing a concentration of 2000x averaged over the receiver entrance with spillage < 2%. The overall annual averaged efficiency, defined as (total sunlight energy delivered to the receiver entrance)/(direct normal irradiance × total reflector area) is >80%. This calculation includes 90% reflectivity of the mirrors.

To avoid the high mass and cost of a structure which must withstand 85 mph winds, our unique arc support structure takes the form of four lightly built panels which are lowered to the ground in high wind and for maintenance. Cables from the central tower are used to lower and raise the panels into operating position where they are locked together. The top section of the tower carrying the cable mechanism and the receiver rotate on a bearing in synchronization with the track mounted reflector assembly.

The small scale of the collector unit means that a first prototype of the radical new architecture can be built and tested at relatively modest cost. Higher power systems with multiple collectors and receivers might be built either with individual storage and turbines, such as sCO2, or with heat transfer to a common storage and power generation facility (as in trough systems). Continual improvements of the collector should be affordable, as system iteration costs are low.

Commentary by Dr. Valentin Fuster
2016;():V001T04A020. doi:10.1115/ES2016-59619.

The central receiver power tower (CRPT) with a particle heating receiver (PHR) is a form of concentrating solar power (CSP) system with strong potential to achieve high efficiency at low cost and to readily incorporate cost-effective thermal energy storage (TES). In such a system, particulates are released into the PHR, and are heated to high temperature by concentrated solar radiation from the associated heliostat field. After being heated, the particles will then typically flow into the hot bin of the TES. Particulates accumulated in the hot bin can flow through a heat exchanger to energize a power generation system or be held in the hot TES storage bin for later use such as meeting a late afternoon peak demand or even overnight generation. Particles leaving the heat exchanger are held in the low temperature bin of the TES.

A critical component in such a PHR system is the particle lift system, which must transport the particulate from the lower temperature TES bin back to the PHR. In our baseline 60 MW-thermal (MW-th) design, the particulate must be lifted around 70 m at the rate of 128 kg/s. For the eventual commercial scale system of a 460 MW-th design the particulate must be lifted around 138 m at the rate of 978 kg/s. The obvious demands on this subsystem require the selection and specification of a highly efficient, economical, and reliable lift design.

After an apparently exhaustive search of feasible alternatives, the skip hoist was selected as the most suitable general design concept. While other designs have not been dismissed, our currently preferred somewhat more specific preliminary design employs a Kimberly Skip (KS) in a two-skip counterbalanced configuration. This design appears to be feasible to fabricate and integrate with existing technology at an acceptably low cost per MW-th and to promise high overall energy use efficiency, long service life, and low maintenance cost. A cost and performance model has been developed to allow optimization of our design and the results of that study are also presented. Our developed design meets the relevant criteria to promote cost effective CSP electricity production.

Commentary by Dr. Valentin Fuster
2016;():V001T04A021. doi:10.1115/ES2016-59646.

In an effort to increase thermal energy storage densities and turbine inlet temperatures in concentrating solar power (CSP) systems, focus on energy storage media has shifted from molten salts to solid particles. These solid particles are stable at temperatures far greater than that of molten salts, allowing the use of efficient high-temperature turbines in the power cycle. Furthermore, many of the solid particles under development store heat via reversible chemical reactions (thermochemical energy storage, TCES) in addition to the heat they store as sensible energy. The heat-storing reaction is often the thermal reduction of a metal oxide. If coupled to an Air-Brayton system, wherein air is used as the turbine working fluid, the subsequent extraction of both reaction and sensible heat, as well as the transfer of heat to the working fluid, can be accomplished in a direct-contact, counter-flow reoxidation reactor. However, there are several design challenges unique to such a reactor, such as maintaining requisite residence times for reactions to occur, particle conveying and mitigation of entrainment, and the balance of kinetics and heat transfer rates to achieve reactor outlet temperatures in excess of 1200 °C. In this paper, insights to addressing these challenges are offered, and design and operational tradeoffs that arise in this highly-coupled system are introduced and discussed.

Commentary by Dr. Valentin Fuster
2016;():V001T04A022. doi:10.1115/ES2016-59654.

An ammonia thermochemical energy storage system consists of an endothermic reaction that disassociates ammonia into hydrogen using the solar energy, which can be stored for future use. The reverse reaction is carried out in the energy recovery process; the ammonia synthesis reaction is used to heat supercritical steam to temperatures on the order of 650 degrees Celsius as required for a supercritical steam Rankine cycle. The goal of this paper is to investigate the transient response in a synthesis reactor-heat-exchanger. It is desired to predict the time the system takes to reach steady state and the effect a perturbation has on the temperature response of the system. A numerical model has been developed to investigate the transient behavior of an ammonia synthesis reactor-heat exchanger. The model consists of a transient one dimensional concentric tube counter-flow reactor-heat exchanger. The effect of gas mass flow rate and initial gas temperature was investigated. Results show that as gas mass flow rate increases, the time for the outlet steam temperature to reach steady state decreases. For low gas mass flow rates, the required outlet steam temperature is not achieved.

Commentary by Dr. Valentin Fuster
2016;():V001T04A023. doi:10.1115/ES2016-59655.

Particle Heating Receivers (PHR) offer a range of advantages for concentrator solar power (CSP). PHRs can facilitate higher operating temperatures (>700°C), they can allow for inexpensive direct storage, and they can be integrated into cavity receiver designs for high collection efficiency. In operation, PHRs use solid particles that are irradiated and heated directly as they fall through a region exposed to concentrated sunlight. The heated particles can subsequently be stored in insulated bins, with the stored thermal energy reclaimed via heat exchanger to secondary working fluid for the power cycle in CSP. In this field Georgia Tech has over five years’ experience developing PHR technology through the support of the DOE SunShot program and similar research efforts. Georgia Tech has dealt with the crucial challenges in particle receiver technology: particulate flow behavior, particulate handling, and particulate heat transfer. In particular, Georgia Tech has specialized in innovative advances in the utilization and design of discrete structures in PHRs (DS-PHR) to prolong particulate residence time in the irradiated zone.

This paper describes the development and results of lab-scale testing for DS-PHRs especially in the Georgia Tech high flux solar simulator (GTHFSS). The GTHFSS is a bank of high intensity xenon lamps with elliptical reflectors designed to replicate a concentrated solar source. Two series of tests have been undertaken: batch and continuous operation. Initially the DS-PHR has been tested in a batch apparatus in which a substantial but still limited quantity of preheated particulate flows through from an elevated bin through the irradiated PHR into a weighing box collecting bin. The use of a weighing box is advantageous since the flow rate of particulate is otherwise especially hard to measure. Temperature rise measurements and mass flow rate measurements allow calculation of energy collection rates. Calorimetry measurements, also described in the paper, are used to verify the incident concentrated radiation allowing the calculation of the collection efficiency. This preliminary series of experiments have been completed using the batch apparatus, with the efficiencies of the lab-scale DS-PHR being determined for a range of temperatures. Efficiencies above 90% have been measured at low temperatures roughly corresponding to the so-called optical efficiency, which is the rate of energy collection at low temperature and minimal heat loss. Batch experiment data indicates a collection efficiency of approximately 81–85% at an average particle operating temperature of 500°C. Lab-scale batch results at 700°C in proved to be unstable, and as such a rework employing a continuous recirculation loop is underway.

While the batch apparatus is convenient for preliminary work, it is challenging to reach steady state operation in the mixing and measurement section below the DS-PHR, which limits this apparatus in higher temperature experiments. Consequently, the experiment is being reconfigured for continuous flow, in which the particulate will be heated and recirculated by a high temperature air conveyor. The advantage of the high temperature conveyor has already been proved by its successful integration as a heater and mixer in the hot bin of the batch apparatus. Such a compact device was also quite advantageous in the limited confines of a typical laboratory simulator such as the GTHFSS. While continuous flow prevents the exceedingly desirable use of an uninterrupted mass measurement device, highly accurate mass flow data is still expected based on the use of a perforated plate flow control station. This device relies on the Berverloo effect to maintain a constant flow of particulate through an array of orifices, for which the flow is largely independent of upstream conditions. A weighing box will be used to calibrate and verify the mass flow. This paper will report on efficiency measurements with the batch flow experiments and present the preliminary steps taken to conduct the recirculation experiment. The bulk the research reported in the paper is sponsored by and done in support of the DoE Sun Shot initiative.

Commentary by Dr. Valentin Fuster
2016;():V001T04A024. doi:10.1115/ES2016-59660.

Thermochemical energy storage (TCES) offers the potential for greatly increased storage density relative to sensible-only energy storage. Moreover, heat may be stored indefinitely in the form of chemical bonds via TCES, accessed upon demand, and converted to heat at temperatures significantly higher than current solar thermal electricity production technology and is therefore well-suited to more efficient high-temperature power cycles. The PROMOTES effort seeks to advance both materials and systems for TCES through the development and demonstration of an innovative storage approach for solarized Air-Brayton power cycles and that is based on newly-developed redox-active metal oxides that are mixed ionic-electronic conductors (MIEC). In this paper we summarize the system concept and review our work to date towards developing materials and individual components.

Commentary by Dr. Valentin Fuster
2016;():V001T04A025. doi:10.1115/ES2016-59692.

A low-cost rigid foam-based concentrator technology development program was funded by the DOE SunShot Initiative to meet installed cost goals of $75/m2 vs. current costs of ∼ $200–250/m2. Phase 1 of the project focused on design trades and cost analyses leading to a cost-optimized self-powered autonomous tracking heliostat concept with a mirror surface area in the 100m2 range. In Phase 2 30-year accelerated testing of the mirror modules based on ReflecTec film with 94% specular reflectivity bonded on composite foam substrate were initiated and completed in Phase 3. The tests with 15 coupons showed optical performance degradation of less than 5% in specular reflectance following 30-year equivalent UV testing and other abuse testing such as acid rain, bird dropping, thermal cycling, etc. A small scale prototype (3m×2m) heliostat design based on modular truss elements with removable mirror modules was developed in detail. In this phase components such as the dual-axis actuators were sized and selected based on wind load requirements and pointing accuracy demands were completed. Finite Element analyses for the mechanical structure with mirror modules were performed using three separate commercial codes — ANSYS, COMSOL and SolidWorks to validate the optical errors induced by wind loads on the structure up to 35 mph. Results indicated that the RMS deflections contributed to less than 0.4 mrad pointing error. Dynamic response of the heliostat indicated that the first 5 eigenmodes were in the 17–20 Hz range. The individual structure elements such as the trusses and c-rails were fabricated locally and assembled with the mirror facets in the lab for initial fit check and testing. The nine mirror facet surface errors were characterized using photogrammetry and verified using Reverse Hartmann techniques and showed to be in the order of 1 mrad or less. A three-level controller (main, gateway and heliostat) was architected and built. Tracking of the sun is done using NREL’s Sun Tracking Algorithm implemented in the gateway controller. Target-pointing vectors are calculated for each heliostat and conveyed wirelessly to the individual heliostat controllers for actuating the azimuth and elevation motors. The power subsystem consisting of solar panels and a battery provide 24V for the actuators and controller boards. The system was sized to provide adequate power for a period of 5hrs of operation when power is not available. Initial calibration will be performed with on-site camera tracking the sun’s image on a target located approximately 52m from the heliostat. Testing of the heliostat pointing under calm and windy conditions will be done to demonstrate overall performance that meet DOE targets of 4 mrad under 27mph winds. Commercialization efforts are underway to transition the design to the commercial sector. The project is well on its way to approaching overall cost targets and current estimates are approximately $90–110/m2 and lower costs can be achieved with alternates to the film we have identified.

Commentary by Dr. Valentin Fuster
2016;():V001T04A026. doi:10.1115/ES2016-59693.

Bladed structures offer an approach to improve the efficiency of conventional concentrating solar power (CSP) cylindrical receivers, due to improved light-trapping via the cavity effect, and by allowing more tubes to be compressed into a smaller aperture, enabling the flux on the aperture to be increased without exceeding the peak flux limitation on individual tubes. In this paper, we present an optical model of a hypothetical bladed receiver mounted on the tower of the Sandia National Solar Thermal Test Facility (NSTTF). We examine the impact of receiver geometric parameters including receiver width, receiver height, number of blades, blade depth and blade angle, through analysis using ‘Tracer’, an open-source Python-based Monte Carlo ray tracing library. Validation of Tracer is provided, through comparison with results from other tools. At the optimal configuration, 15 blades with a depth of 4.5 m and angle of 63.9° from the vertical are spaced vertically over a 9.6×9.6 m back wall. In this configuration, the peak flux occurs on the back plane and is considerably lower than a corresponding flat receiver. The design-point receiver optical efficiency increases from 93.8% for a flat receiver to 98.5% for the bladed configuration, and is shown to be robust to sun position changes.

Commentary by Dr. Valentin Fuster
2016;():V001T04A027. doi:10.1115/ES2016-59703.

The performance of the tower based concentrated solar thermal (CST-tower) plant is very sensitive to the operation strategy of the plant and the incident heat flux on the receiver. To date, most studies have been examined only the design mode characteristics of the cavity receivers, but this paper significantly expands the literature by considering non-design operating conditions of this important sub-component of the CST-tower plants. A feasible non-design operating conditions of the cavity receivers that was considered in this study is the storage mode of operation. Two practical dynamic control strategies were examined then to find the most efficient approach: fixed solar field mass flowrate (Approach “A”) and fixed outlet temperature at receiver (Approach “B”). To evaluate the performance of the cavity receiver, a thermal model is developed to be used for design and non-design analysis. The thermal model has been then validated against available data from the Gemasolar operating solar Tower plant. In non-design conditions, the effects of heat transfer fluid (solar salt) temperature and flowrate are mainly evaluated in terms of the non-dimensional receiver thermal output, non-dimensional power output, receiver energetic efficiency, receiver surface temperature, receiver outlet temperature, and the fraction of solar field usage. The results of this study (e.g. off design receiver efficiency correlations) assist researchers to evaluate cavity receivers without performing detail simulations. They also help investigators to choose an appropriate control strategy and to analyze the viability of other CST-tower subcomponents that have thermal interactions with the receiver (e.g. dynamic control of the phase change storage unit or its boundary conditions).

Commentary by Dr. Valentin Fuster

Energy Storage

2016;():V001T05A001. doi:10.1115/ES2016-59053.

A higher number of research institutions work on solutions for energy storage systems. Therefore a large number of differing approaches in competition among each other to develop storage technologies. At the TU-Wien, Institute for Energy Systems and Thermodynamics a novel thermal energy storage concept based on an active fluidized bed technology — the so called sandTES-heat exchanger technology — has been developed. The present paper describes the basic idea behind the key technology and the design methodology of a test rig in semi-industrial scale. In addition the results of selected preliminary experimental and numerical investigations are presented and discussed.

Commentary by Dr. Valentin Fuster
2016;():V001T05A002. doi:10.1115/ES2016-59161.

Most of the renewable energy sources, including solar and wind suffer from significant intermittency due to day/night cycles and unpredictable weather patterns. On the other hand increasing share of renewable sources imposes additional stability risks on the power grid. Increased share of solar energy in power generation during noon along with increased power demand during afternoon peak hours generates a significant risk on the stability of power grid. Energy Storage systems are required to enable the renewable energy sources to continuously generate energy for the power grid and enhance the stability of future grid that benefits from more renewable sources. Thermal Energy Storage (TES) is one of the most promising forms of energy storage. Although round trip efficiency is relatively high in thermal storage systems, heat transfer is a well-known problem of most TES systems that use solid state or phase change. Insufficient heat transfer may significantly impact the performance of the TES system. The TES system of this study utilizes molten sulfur as the storage medium. Although thermal conductivity of molten sulfur is relatively low, the sulfur-based TES system benefits from enhanced heat transfer due to the presence of buoyancy-driven flows. In this study, the effect of natural convection on the heat transfer characteristics of a sulfur-based isochoric TES system is studied computationally and theoretically. It turns out that the viscosity of sulfur in the temperature range of this study (250–400 °C) varies by two orders of magnitude. A computational model was developed to investigate the effect of viscosity variations on the buoyancy-driven flow and corresponding charge and discharge times. The computational model is developed using an unsteady Finite Volume Method by a commercially available CFD package. The results of this study show that the heat transfer process in the isochoric TES element is highly impacted by natural convection. The viscous flow of molten sulfur near the boundaries of the isochoric TES element leads to different charge and discharge times. The discharge time is almost two times longer than the charge time due to formation of a viscous layer of elemental sulfur near the heat transfer surface. The viscous layer of sulfur decreases the activity of the buoyancy-driven flow and decreases the heat transfer rate during discharge cycle. The computational model was validated by comparing the results of a representative case with experimental data.

Commentary by Dr. Valentin Fuster
2016;():V001T05A003. doi:10.1115/ES2016-59219.

The eutectic Na2CO3-NaCl molten salt was investigated as a new high temperature phase change material for solar thermal energy storage. The composition of the eutectic binary salt was determined with the aid of FactSage software and its thermophysical properties were investigated using a Simultaneous Thermal Analyzer, X-Ray Diffraction and a Scanning Electron Microscope. Eutectic Na2CO3-NaCl salt shows higher measurement values in a CO2 atmosphere than these in a N2 atmosphere in terms of heats of both fusion and solidification. Thermal stability analysis indicates that the eutectic molten salt has higher thermal stability in a CO2 environment without weight loss at temperatures below 700 °C compared with 0.51% weight loss at the melting point around 640 °C in a N2 atmosphere. The weight loss observed in the latter, is most likely to be due to the salt’s decomposition at high temperature. The thermophysical properties of the salt such as melting temperature, heats of both fusion and solidification, as well as the phase identification and phase morphology varied slightly after 100, 200 and 300 thermal cycle tests. Therefore, the eutectic Na2CO3-NaCl salt has a good thermal and phase stability. It therefore is a promising high temperature phase change material when used in a CO2 environment.

Commentary by Dr. Valentin Fuster
2016;():V001T05A004. doi:10.1115/ES2016-59249.

All life on earth depends on energy and the cycling of carbon. Energy is essential for economic and social development and also poses an environmental challenge. The world’s dependence on fossil fuels began approximately 200 years ago. Availability of fossil energy resources, peak oil era and this is the time for end of the fossil fuel era, price and environmental impact and various renewable resources and use of it.

The twenty first century is rapidly becoming the perfect energy storm, modern society is faced with volatile energy prices and growing environmental concerns as well as energy supply and security issues. Solar and wind energy are now providing the lowest cost options for economic and community development in rural regions around the globe. Energy and water are the key to modern life and provide the basis necessary for sustained economic development. Due to a growing world population and increasing modernization global energy demand is raising during the current century. Finding the sufficient supplies of clean and sustainable energy for the future is the global society’s most challenge for this century. The future will be depends on a renewable sources such as solar, wind and biomass.

There are large numbers of phase change materials (PCM’S) that melt and solidify at wide range of temperatures, making them attractive in a number of applications. PCMs have been widely used in latent heat thermal storage systems for heat pumps, solar engineering and spacecraft thermal control applications. The use of PCMs for heating and cooling applications for buildings has been investigated within the past decade. The experimental results computed in the field of water distillation process using solar energy in the presence of energy storage materials i.e paraffin wax are discussed in this paper.

Commentary by Dr. Valentin Fuster
2016;():V001T05A005. doi:10.1115/ES2016-59341.

Current trends show that renewable energy production costs continue to decrease with time, so that renewable energy sources (RES) are becoming more suitable as electricity sources. In addition to their environmental benefits, RES are especially appropriate for remote areas, where the expansion of existing power grid is impractical and fuel transportation for thermal generators is too expensive. In this regard, our work studies the optimal capacity sizing for a completely green village (CGV), which is an isolated residential microgrid (MG) whose power is entirely generated by RES. In particular, we consider a neighborhood composed of smart homes that contain programmable appliances, whose operations can be interrupted or automatically scheduled in time. Though there are many works in literature that investigate MG optimal capacity sizing, to our knowledge, our work is the first that utilizes the scheduling of programmable appliance to minimize MG investment costs. To establish the effectiveness of our method, we compare an optimal MG capacity sizing algorithm that utilizes appliances’ programmability (Opt-P) with an algorithm that places appliances into operation as soon as they are ready without shifting in time or preempting their operation (NoSch-P). Our simulation results show that Opt-P reduces the investment cost by at least 42% compared to NoSch-P, when the ratio between the energy storage investment cost per kWh and the RES’ investment cost per kW is greater or equal to 10.

Commentary by Dr. Valentin Fuster
2016;():V001T05A006. doi:10.1115/ES2016-59350.

Advanced compliant foil bearings capable of operating in low ambient pressures associated with soft vacuum are now paving the way to a new type of flywheel energy storage system. Many conventional flywheel energy storage system design approaches use active magnetic bearings with backup bearing technologies to meet the need for high speed operation in a low ambient pressure environment. Low ambient pressures are needed to overcome the power loss limitations associated with windage at high surface speeds. However, bearing technologies that rely on active control tend to be large, are dynamically soft which necessitates backup bearings and require a power supply which consumes some of the stored power to maintain rotor levitation.

In this paper the authors will demonstrate both theoretically and experimentally the ability of advanced 5th generation compliant foil bearings to support large flywheel rotors weighing in excess of 900 N and which can operate to speeds in excess of 40,000 rpm. Testing conducted at pressures as low as 7 kPa demonstrates the ability of foil bearings to operate in low ambient pressures consistent with flywheel energy storage system needs for low windage loss. The authors will also present a hypothesis and the mechanisms involved in a hydrodynamic phenomenon that allows a foil bearing to operate successfully when the mean free path of the air molecules is exceedingly large due to low ambient pressures.

Commentary by Dr. Valentin Fuster
2016;():V001T05A007. doi:10.1115/ES2016-59469.

The ability to efficiently and cost-effectively incorporate thermal energy storage (TES) systems is an important advantage of concentrating solar power (CSP) in comparison to other intermittent forms of renewable energy, such as wind or photovoltaics. As such, TES allows CSP plants to continue to provide electricity to the grid even at times when the resource (the sun) is not available, such as cloud transients or at night. Advanced power cycle systems with supercritical carbon dioxide (sCO2) as the working fluid provide high power conversion efficiency because of high temperatures attained, and less compression work and are being explored for integration with concentrating solar power plants. Currently, there is no cost-effective way to store energy at high temperatures (>565 degree Celsius). The present work analyzes the thermal performance of a novel, cost-effective thermal storage system based on elemental sulfur as the storage media. The analysis is based on a detailed system-level computational modeling of the complex conjugate heat transfer and fluid flow phenomena at multiple scales to provide a scientific basis for engineering, designing and optimizing the novel thermal storage system for transient operation. The validation of the computational model based on data from experiments and full-scale plant operation is also reported. Our studies have shown sulfur-based TES to be a promising candidate for high temperature CSP.

Commentary by Dr. Valentin Fuster
2016;():V001T05A008. doi:10.1115/ES2016-59470.

Efficient and cost-effective thermal energy storage system plays an important role in energy conservation. Elemental sulfur, the thirteenth most abundant element on earth, is actively being researched as a potential thermal storage medium due to its high energy storage density and low cost. The present work investigates the heat transfer behavior of elemental sulfur at temperatures between 50 degree Celsius and 250 degree Celsius. A shell and tube heat exchanger configuration with sulfur stored inside the tubes and heat transfer fluid flowing over the tubes through the shell is considered. A detailed computational model solving for the conjugate heat transfer and solid-liquid phase change dynamics of the sulfur based thermal energy storage system is developed to elucidate the complex interplay between the governing heat transfer and fluid flow phenomena during charge and discharge operations. The developed numerical model is compared with experimental results and a systematic parametric analysis of the effects of various design parameters on the performance of the thermal storage system is reported.

Commentary by Dr. Valentin Fuster

Environmental, Economic, and Policy Considerations of Advanced Energy Systems

2016;():V001T06A001. doi:10.1115/ES2016-59092.

The massive use of fossil fuel has caused huge carbon emission and serious air pollution in China. Now all kinds of alternative energy technology are developing rapidly to solve such problem in China. Electricity produced by non-fossil fuel energy is continued to increase sharply in China. But it’s hard for regular alternative energy, such as wind power, solar power, hydroelectricity power, nuclear power and so on, to easily provide process heat for industry, especially high temperature steam.

High temperature Gas-cooled Reactor (HTGR, sometimes also called HTR) is a kind of nuclear reactor, which are demonstrated very high efficiencies, safety and availability features by American and German power plant. HTR differs from water nuclear reactors by offering a high thermal efficiency for electricity generation and a high level of passive safety features. Now HTR-PM project is built in Shidao Bay of China. Moreover, HTR is the only nuclear reactor, which can provide high temperature steam comparing with other water nuclear reactors. So HTR can provide a versatile cogeneration solution for industry.

In this paper, a case was studied, how to provide heat for a refinery and petro-chemical plant with HTR. Firstly, the energy need of a typical large chemical plant in china was investigated. Steam supply diagram of an oil refinery plant, which produced 10 million tons oil products and 1 million tons ethylene in China, was calculated. Secondly, technical feasibility of energy providing by HTR cogeneration plant was discussed. Extraction steam from HTR system was designed for the chemical plant. It would meet the requirement of steam supply for chemical plant and would replace the captive power plant, where coal was burning. The balance of steam, enthalpy and temperature was calculated. At last, economic evaluation for such cogeneration plants was carried out. The steam supply cost from captive coal power plant and HTR cogeneration plant was compared. Some economical conclusion was made from the discussion.

Commentary by Dr. Valentin Fuster
2016;():V001T06A002. doi:10.1115/ES2016-59320.

This is a first report of a comprehensive effort to determine the nexus between energy demands, population growth, and a changing climate for Mexico region. We first report here Mexico City climatology, trends in temperatures, heat index and heat waves registered in the Valley of Mexico and its potential relation to electricity consumption. The work is motivated by the environmental impacts that densely populated cities such as Mexico City produces manifested by energy consumption and emissions to the environment and direct consequences in the quality of its inhabitants and on the local environment. We used eight weather stations spread over the valley of Mexico to analyze temporal trends of maximum and minimum daily temperatures and relative humidity. The heat index and the human discomfort index are derived as tools to determine trends in environmental variables that may be linked to energy demands in the Valley. The actual power consumption in the valley of Mexico are further analyzed for formulating relationship between power consumption and maximum temperatures during long-term scenarios and during specific extreme heat events. The relationship between power consumption with changes in the population in the valley of Mexico is also investigated.

Commentary by Dr. Valentin Fuster
2016;():V001T06A003. doi:10.1115/ES2016-59425.

Net metering is an incentive that is essential to most solar photovoltaic systems. Recently the burden placed upon local utilities is an issue some regulators have been asked to address. This research uses actual 2013 and 2014 solar production data from nearly 200 sites, wholesale electricity day-ahead pricing data, and utility-wide demand data. This is all analyzed by the hour for two full years for a western Pennsylvania based utility and an eastern Pennsylvania based utility and their wholesale generators. Results show electricity is 15% more valuable when solar PV systems are generating power and feeding the grid during good weather conditions than at night or cloudy days when solar customers get energy back from the grid.

Solar energy generation is highly predictable in the day-ahead market, and leads to suppression in market prices for electricity. Thus to reveal the true impact of this market suppression, an increased solar renewable portfolio standard (RPS) fraction of 0.2 to 10% was simulated. This caused a decrease in demand resulting in a corresponding reduction in the price of electricity yielding savings to the utility. The maximum rate of increase and decrease in the utility-wide load did not change significantly until the solar RPS exceeded 5%. Additionally, the demand for electricity was reduced during the highest load hours of the year that corresponded to the most expensive hours of the year. The minimum base-load of the year was decreased substantially for solar RPS of 5% or greater and the base load reaches zero for solar RPS over 10%.

From the data of these two years, it is demonstrated that an increased use of solar energy would lead to savings that are larger than the loss in revenue due to having fewer traditional non-solar customers. Thus electricity suppliers and utilities stand to have both higher profits and higher profit margins when customers adopt net-metered solar energy compared to the non-adoption of solar energy.

Topics: Solar energy
Commentary by Dr. Valentin Fuster
2016;():V001T06A004. doi:10.1115/ES2016-59501.

With the proposed Clean Power Plan for regulating carbon emissions from the power sector in the U.S, policymakers are likely to use a cost optimization framework to plan for future scenarios and implementation strategies. The modeling framework introduced in this paper would help such policymakers to make the appropriate investment decisions for the power sector. This paper applies an analytical model and an optimization model to investigate the implications of coimplementing an emission cap and a Renewable Portfolio Standards (RPS) policy for the U.S. Northeast. A simplified analytical model is specified and the first order optimality conditions are derived. The results from the analytical model are verified by running simulations using LP-CEM, a linear programming-based supply cost optimization model. The LP-CEM simulation results are analyzed under the recently proposed Clean Power Plan emissions cap rules and RPS scenarios for the U.S. Northeast region. The marginal abatement cost estimates, derived from a limited set of LP-CEM runs, are analyzed and compared to the theoretical results. For encouraging renewables generation, an RPS instrument is cost-effective at higher policy targets, while an emissions cap instrument is cost-effective at lower policy targets. For CO2 emissions reduction, an emissions cap instrument is found be cost-effective for all policy targets. There is a trade-off between emissions levels and supply costs when the two instruments are co-implemented.

Commentary by Dr. Valentin Fuster
2016;():V001T06A005. doi:10.1115/ES2016-59531.

The objective of this study was to determine the effects of harvest time and drying techniques on the energy requirements and profitability of grain production, particularly corn (Zea mays). In most grain production scenarios, supplemental drying is required post-harvest to allow long-term storage of the crop. Traditional high-temperature, high airflow drying systems have been known to be an energy intensive and high cost process of grain production. However, advanced continuous flow drying systems have shown to be 30% or more energy efficient than systems produced in recent decades. In this study, harvesting times (early fall, mid-fall, late fall) were compared to quantify the effects of field losses as the fall progresses with the potentially reduced drying requirement as the crop undergoes natural drying in the field. A model was developed to investigate the energy and economics of drying, based on harvest period, dryer efficiency, field drydown, and field losses. A sensitivity analysis was completed that focused on the energy consumption of artificial drying based upon harvesting conditions, as well as economic factors of field drying and fuel cost. Preliminary results of the study have shown that the use of higher efficiency drying systems combined with moderately prompt harvest times generally provide the most profitable scenario, while delayed harvest times increase the likelihood of field loss, which are not typically offset by the reduced drying requirements.

Commentary by Dr. Valentin Fuster
2016;():V001T06A006. doi:10.1115/ES2016-59673.

This paper proposes a national energy efficiency policy to go along with the Development Plan of the State of Kuwait 2015–2020. Obstacles hindering the energy savings including, the general consensus of government officials, securing national energy funds, engaging various stakeholders, setting targets and establishing benchmarks and legal framework to monitor and gage progress are discussed. A SWOT analysis is conducted to arrive at short term (5 years) and long term (15 years) milestones for the policy roadmap needed to achieve optimum potential saving. Compared with the present consumption pattern (business as usual), primary energy saving will reach 2.4% by 2020 and extending to 30% saving by 2035. This saving target is the result of analyzing various policy scenarios through the application of energy conservation code, building energy audits, appliance labeling, building labeling, smart building energy monitoring and control, vehicle energy labeling, and electric vehicles.

Commentary by Dr. Valentin Fuster

Geothermal, Ocean, and Emerging Energy Technologies

2016;():V001T07A001. doi:10.1115/ES2016-59123.

In this work an emerging hydrokinetic energy technology, Tethered UnderSea Kites (TUSK), is studied. TUSK systems use an axial-flow turbine and generator mounted on a rigid, underwater winged kite that is tethered to a floating surface buoy to extract power from an ocean current. The tethered underwater kite is controlled to travel in cross-current motions at a high velocity which is at least four to five times larger than the ocean current velocity. This higher velocity significantly increases the potential power output compared to conventional fixed marine turbines. Modeling and simulation of the kite-tether dynamics in a TUSK system is studied by developing and solving governing equations of motion derived from Euler-Lagrange equations. Models for physical effects appropriate to TUSK systems are developed, including for turbine power and turbine drag, kite wing hydrodynamic forces, and the effect of turbine blade tip cavitation on turbine power output. A baseline simulation that includes these modeled effects and a simple kite control scheme is studied to estimate cross-current kite trajectories, turbine power output, kite hydrodynamic forces, kite pitch, roll and yaw dynamics, and tether tensions. Once the baseline simulation case has been fully explored, a parametric study is conducted that varies key design and flow parameters including ocean current speed, kite weight and wing area, turbine rotor area, tether length, and kite control system parameters.

Topics: Simulation , Modeling
Commentary by Dr. Valentin Fuster
2016;():V001T07A002. doi:10.1115/ES2016-59363.

Recently, rectennas have drawn attention as an attractive option to harvest radiative thermal energy from the sun and terrestrial thermal sources. In order to achieve the potential high energy conversion efficiencies by this technology, matching conditions between the incident electromagnetic wavelength and the rectenna characteristic length must be satisfied. Therefore, a selective emitter is a key element in high efficiency rectennas. Photonic structures were designed for selective emission using the transfer matrix method and genetic algorithm optimization. Two types of emitters were developed using aluminum as the supporting substrate. This paper presents narrowband selective emitters with a peak emissivity at 9.45 μm made of alternating layers of Al2O3 and SiO2 on a substrate, and broadband selective emitters made of alternating layers of Al2O3 and SiC on a substrate with a high emissivity band between 9.5 μm and 10.5 μm.

Commentary by Dr. Valentin Fuster
2016;():V001T07A003. doi:10.1115/ES2016-59532.

Mixing of fresh (river) water and salty water (seawater or saline brine) in a control fashion would produces an electrical energy known as salinity gradient energy (SGE). Two main conversion technologies of SGE are membrane-based processes; pressure retarded osmosis (PRO) and reverse electrodialysis (RED). In PRO, semipermeable membranes placed between the two streams of solutions allow the transport of water from low-pressure diluted solution to high-pressure concentrated solution. RED requires two alternating semipermeable membranes that allow the diffusion of the ions but not the flow of H2O. Lifetime and power density of the semipermeable membrane are two main factors affecting on deployment of PRO and RED. Semipermeable membranes with lifetime greater than 10 years and power density higher than 5 W/m2 would lead to faster development of this conversion technology.

An exergy analysis of an SGE system of sea-river can be applied to calculate the maximum potential power for electricity generation. Seawater is taken as reference environment (global dead state) for calculating the exergy of water since the seawater is the final reservoir. Once the fresh water is mixed with water of the sea or lake it becomes unuseful for human, agricultural or industrial uses loses all its exergy. Aqueous sodium chloride solution model is used in this study to calculate the thermodynamic properties of seawater. This model does not consider seawater as an ideal model and provides accurate thermodynamics properties of sodium chloride solution. As a case study, exergy calculation of Iran’s Urmia Lake-GadarChay River system. The chemical exergy analysis considers sodium chloride (NaCl) as main salt in the water of Lake Urmia. The sodium chloride concentration is more than 200 g/L in recent years. Based on the exergy results the potential power of this system is 329 MW. This results indicates a high potential for constructing power plant for salinity gradient energy conversion.

Commentary by Dr. Valentin Fuster


2016;():V001T08A001. doi:10.1115/ES2016-59075.

The main focus area of this research paper to efficiently remove the heat generated during conversion of solar energy into electricity using photovoltaic (PV) module. The photovoltaic conversion efficiency of commercial available PV module varies in the range of 8%–20% depending on the type of solar cell materials used for the module construction, e.g. crystalline silicon, thin film, CIGS, organic, etc. During the conversion process, only a small fraction of the incident solar radiation is utilize by PV cells to produce electricity and the remaining is converted into waste heat in the module which causes the PV cell temperature to increase and its efficiency to drop. This thermal energy could be extract using air or water as a heat removal fluid to utilize in heating applications. The purpose of a solar photovoltaic module is to convert solar energy into electricity. The hybrid combination of photovoltaic module and thermal collector called Photovoltaic-thermal (PVT) module. Such PVT module combines a PV, which converts electromagnetic radiation (photons) into electricity, with a solar thermal module, which captures the remaining energy and removes waste heat from the PV module. Cooling of cells either by natural or forced circulation can reduce the PV cell temperature. The simultaneous cooling of the PV cells maintains their PV efficiency at a satisfactory level and offers a better way of utilizing solar energy by generating thermal energy as well. PVT system has higher overall efficiency as compared to separate PV and thermal collector. The heat output of a PVT module can be used for space heating or production of domestic hot water.

This paper presents an innovative design of top cooling Thermal Photovoltaic (T-PV) module and its performance under outdoor weather condition of Singapore. T-PV collector is designed to flow fluid over the top of PV panel through a very narrow gap between the solar lens. This process improves heat removal process from PV panel, and hence, improves the electrical output of PV panel as compared to other PVT collector available in the market. By flowing the water from top of the PV panel will also provide better thermal efficiency. A T-PV collector system with storage tank, sensors, pump, flow meters, data logger and controls, have been installed at test-site located in Ngee Ann Polytechnic, Singapore. Performance analysis of T-PV collector system has been evaluated under the tropical climatic conditions of Singapore. It was found that T-PV module could produce additional electrical power as compared to standard PV panel of same capacity by operating at lower temperature. In addition to electricity, T-PV panel also generate the hot water up to 60 deg C at an average thermal efficiency of 41% for usage in residential and commercial buildings. The average thermal energy output was 3.1 kWh/day on typical day’s basis.

Topics: Cooling
Commentary by Dr. Valentin Fuster
2016;():V001T08A002. doi:10.1115/ES2016-59366.

Augmenting photo-voltaic (PV) system performance using fixed flat mirrors boosts PV power output. Previous literature reports that fixed flat mirrors create non-uniform irradiance on the PV panels, which limits the current and decreases panel efficiency. Triplex panels have a modified cell string architecture that splits the panel into three separate sections to address this problem. This paper describes an experimental setup consisting of a pyranometer to measure total solar irradiation, an air temperature sensor, a standard PV panel with and without mirrors, and a triplex panel with and without mirrors. The sensor and PV panels are connected to Daystar Multi-tracer logger to collect the instantaneous data. The experiment is simulated using TracePro® to determine the distribution of radiation reflected onto the PV panels. Both simulated and measured results indicate the bottom part of the mirror augmented panels receive the most solar irradiance followed by middle portion, followed by top portion. The results document the difference in performance between standard and Triplex panels with fixed flat mirrors and suggest configurations that maximize performance.

Commentary by Dr. Valentin Fuster
2016;():V001T08A003. doi:10.1115/ES2016-59384.

In this paper, experiments that can be introduced to Clean Energy Systems classes are described. The experiments investigate the effect of power characteristics (temperature, shade and tilt angle) on solar panel electricity production. Solar cell efficiency is the ratio of the electrical output of a solar cell to the incident energy in the form of sunlight. The energy conversion efficiency of a solar cell is the percentage of the solar energy to which the cell is exposed that is converted into electrical energy. Extreme temperatures can cause a decrease in solar panel’s power output and airstream can dissipate the heat and bring the solar panel to its normal operating condition. Solar panel efficiency is undesirably affected by heat and improved with introducing cooler medium.

As well as heat, solar panel loses its power when a part of it is shaded by trees or surrounding buildings. Before solar panel systems are designed for homes, usually a detailed shading analysis of the roof is conducted to reveal its patterns of shade and sunlight throughout the year.

By the same manner, how solar panels react to the direct and indirect rays from the sun in order to produce electricity is examined through experiments. Voltage, current and power flowing into a resistor are measured when the angle of the solar panel relative to the light source is changed. The tilt angles to the electrical measurements are linked to the differences in electrical generation.

Students can perform experimental procedures explained here and gain the conceptual understanding of the Solar Energy better. The investigations require student explanation of the question, method, display of data with the critical response from peers.

Commentary by Dr. Valentin Fuster
2016;():V001T08A004. doi:10.1115/ES2016-59390.

In a previous study, using field measurement data from the Qatar Foundation Solar Test Facility, the daily change in Cleanness Index (CI), a measure of PV performance ratio, corrected for temperature and normalized to a clean PV module, was correlated to environmental variables including airborne particulate matter concentration (PM10), wind speed (WS), and relative humidity (RH). A linear empirical equation between daily CI change and the daily average PM10, WS, RH was developed using Microsoft Excel®. However, the model was not extensively evaluated due to the small data set available then. In this study, a larger data set was used to fit the linear model for daily CI change and daily average values of PM10, WS, and RH. In addition, a semi-physical model was developed to take into account the non-linear mechanics of turbulent deposition, resuspension of deposited dust, and the effect of relative humidity on resuspension. The regression and solver functions of Microsoft Excel® was employed to fit the data. The R-squared values of the linear model and the semiphysical model are 0.0949 and 0.1774, respectively. The semi-physical model predicts the daily ΔCI slight more accurately than the linear model. However, for prediction of cumulative ΔCI over longer periods of time, the two models perform roughly the same. Overall, both models are able to predict the two-month ΔCI with an uncertainty of less than 16%. The results from this study suggest that it is possible to use mathematical models to calculate PV power output degradation in the Doha, Qatar area. This may be a significant step towards development of models that can be used for economic analysis of PV solar projects and plant maintenance.

Commentary by Dr. Valentin Fuster
2016;():V001T08A005. doi:10.1115/ES2016-59411.

The photovoltaic output power is directly proportional to the solar radiation and inversely with the cell temperature. The higher the photovoltaic temperature is, the lower the electrical efficiency is with possible damage to the cell. To improve the electrical efficiency and to avoid the possible damage, a concentrating PV system associated with an effective cooling technique is of great importance. In the present study, a new cooling technique for concentrated photovoltaic (CPV) systems was introduced using various designs of micro-channel heat sinks. The suggested configurations included parallel flow, counter flow single and double layer micro-channels, and single layer flat micro-channel integrated with CPV system. A comprehensive three-dimensional thermo-fluid model for photovoltaic layers integrated with microchannel heat sink was developed. The model was simulated numerically to estimate the solar cell temperature. The numerical results were validated with the available experimental and numerical results. In the meantime, the effects of different operational parameters were investigated such as solar concentration ratio and cooling mass flow rate. Performance analysis of CPV using different microchannel configurations was implemented to determine the average and local solar cell temperature, pumping power, and temperature uniformity. Results indicated that the use of microchannel heat sink was a very effective cooling technique which highly attained temperature uniformity, viz., eliminated the hot spots formation with a significant reduction in the average temperature of CPV. The single layer parallel flow achieved the minimum solar cell temperature while the counter flow attained the most uniform temperature distribution compared with other configurations. Furthermore, the double layer parallel flow microchannel attained the minimum pumping power for a given cooling mass flow rate.

Commentary by Dr. Valentin Fuster
2016;():V001T08A006. doi:10.1115/ES2016-59641.

The contribution of renewable energy to the worldwide sustainable development and environmental preservation has been widely recognized nowadays. Concentrated photovoltaic (CPV) system, in particular, has received an extensive research effort as one of the most promising applications of solar energy. Due to the high concentration r1atio, a significant increase in the CPV temperature occurs. Consequently, the conversion efficiency deteriorates; thereby thermal regulation of a CPV system is of great importance. Therefore, a hybrid system including CPV, and phase change material (PCM) is considered as a single module to achieve higher solar conversion efficiency. Such a system provides a high-energy storage density at a constant temperature which corresponds to the phase transition temperature of the material. In the present study, a comprehensive model for CPV layers integrated with PCM was developed. This model was a coupled of a thermal model for CPV layers and fluid dynamic heat transfer model that took into account the phase-change phenomenon using enthalpy method, and the conversion of solar incident radiations. The effects of specific two variables on the solar cell temperature were investigated which were the PCM thickness of 50, 100, and 200 mm and concentration ratio (CR) from 5 to 20. It was found that the use of PCM could achieve a significant reduction of solar cell temperature. The solar cell temperature reduced from 180 °C to 38 °C by using PCM of thickness 200 mm at CR=5, while at the same PCM thickness, the cell temperature reduced from 510°C to 64°C at CR=20. Furthermore, the solar cell temperature was maintained at an average temperature of 38 °C for 8.4 hours using a 200 mm thickness of PCM at CR=5. In addition, at CR=20, the solar cell temperature was maintained at an average temperature of 64 °C for 2.0 hours using a 200 mm thickness of PCM. From the results, it was indicated that the use of PCM was an effective cooling technique since it attained a significant reduction in solar cell temperature, especially at high concentration ratio.

Commentary by Dr. Valentin Fuster


2016;():V001T09A001. doi:10.1115/ES2016-59372.

Bi-directional turbines convert oscillating axial fluid flow into uniform radial rotation and have proven effective in wave energy harvesting applications, like ocean wave generators. Two of the most widely studied designs for these scenarios are the Wells and axial turbines. This study characterizes the effectiveness of these turbines for use with a thermoacoustic generator; which is a relatively new technology that uses an induced temperature gradient to propagate acoustic waves within an enclosed, looped chamber. These generators are widely applied to refrigeration cycle systems; yet when paired with a bi-directional turbine, the resulting sound wave can be harnessed to generate electricity.

This paper begins with a discussion of the thermoacoustic application covering relevant issues for the turbine. Next, the Wells, axial, and a combined hybrid turbine are presented in thorough detail including governing design features that were explored. Fabrication of a test fixture and turbine prototypes and experimental results from a broad ranging study of the performance of the turbine designs is shown. Finally, conclusions from the obtained results are discussed.

Commentary by Dr. Valentin Fuster
2016;():V001T09A002. doi:10.1115/ES2016-59542.

Heat exchanger takes important role in economic feasibility for Ocean Thermal Energy Conversion (OTEC) or Sea Water Air Conditioning (SWAC) systems. As the portion of heat exchanger made of titanium (Ti) with anti-corrosion function against seawater is more than 20∼30% of total initial cost, the economical feasibility can be enhanced by replacing titanium with cheaper corrosion-resistant materials or treatment methods. This study carry out to examine the corrosion-resistant property of Electrodeposited Oxy-Nitriding Steel (EONS) plate, it turns out life time of the EONS plate is more than 13.9 years. Also, the heat transfer performance for condensation and evaporation of the EONS plate heat exchanger were found to be 11.3% and 7% higher than those of Ti plate heat exchanger. If the life time of the EONS plate of 13.9 years compared to the Ti plate which could be assumed about 30 years, then practical application is possible whether its production cost is found to be less than 46.5% of Ti plate. Lower cost of mass-producing EONS plate by 45% than existing Ti plate seems to enable the substitution in OTEC and SWAC.

Commentary by Dr. Valentin Fuster
2016;():V001T09A003. doi:10.1115/ES2016-59577.

On the way to a de-carbonized economy by 2050 new technologies have to be developed and deployed into the market. In solar driven thermochemical processes concentrated solar radiation is used as a renewable high temperature heat source to drive a chemical reaction. These processes are promising pathways for the production of gaseous and liquid fuels and therefore they can provide sustainable chemical energy carriers with inherent long-term storage capabilities. Amongst these processes, redox cycles for the production of syngas from water and carbon dioxide received considerable interest due to their high theoretical process efficiencies. In these processes a redox material is reduced using high temperature heat which is provided by concentrated solar radiation. In a second reaction, at considerably lower temperatures, the redox material is oxidized while splitting water or carbon dioxide. One requirement for the design of efficient redox processes is a high recovery rate of the sensible heat of the solid redox material. In recent redox process concepts the use of inert heat transfer particles in combination with a particulate redox material has been proposed. Amongst other benefits this methodology allows to recover heat from the redox material. A corresponding solid-solid heat recovery system is under development. In a single stage the heat recovery unit acts as a co-current heat exchanger. By combining several units and by using a proper flow path a quasi-counter-current heat exchanger can be obtained. Such a heat recovery system requires that particles are lifted at temperatures well above 1100°C. These high temperatures require a simple design, decent thermal insulation and the thermal shielding of all moving parts and engine. The present work is dealing with the development of a respective conveying system which can be operated at the targeted temperatures, while heat losses are prevented as far as possible. A lab scale version of the conveyer is constructed and tested. A numerical model of the conveyer is developed and validated using results of an experimental campaign with particles at 1150°C. The next step in the assessment of the conveyer system is the analysis of the performance of a scale up version. A generic process analysis will be conducted to obtain operational and design requirements of the scale up conveyer. A detailed scale up version is developed accordingly and the validated numerical model is applied to this design to predict the heat losses during the particle lifting and to discuss their impact on the total process performance.

Commentary by Dr. Valentin Fuster

Solar Chemistry

2016;():V001T10A001. doi:10.1115/ES2016-59167.

Within the European research project SOL2HY2, key components for a solar hybrid sulfur cycle are being developed and demonstrated at pilot scale in a real environment. Regarding the thermal portion, a plant for solar sulfuric acid decomposition is set up and initially operated at the research platform of the DLR Solar Tower in Jüulich, Germany.

One major component is the directly irradiated volumetric receiver, superheating steam and SO3 coming from a tube-type evaporator to above 1000 °C. At the design flow rate of sulfuric acid (50%-wt.) of 1 l/min, a nominal solar power of 57 kW is required at the receiver. With a flat ceramic absorber made from SiC and a flat quartz glass window, the design is based on lab scale reactors successfully demonstrated at the solar furnace of the German Aerospace Centre (DLR) in Cologne, Germany.

A flexible lumped thermodynamic tool representing the receiver, compiled to assess different configurations, is presented in detail. An additional raytracing model has been established to provide the irradiation boundaries and support the design of a conical secondary concentrator with an aperture diameter of 0.6 m. A comparison with first experimental data (up to 65% nominal power), obtained during initial operation, indicates the models to be viable tools for design and operational forecast of such systems. With a provisional method to account for the efficiency of the secondary concentrator, measured fluid outlet temperatures (up to 1000 °C) are predicted with deviations of ±60 °C. Respective absorber front temperatures (up to 1200 °C) are under-predicted by 100–200 °C, with lower deviations at higher mass flows. The measured window temperature (up to 700 °C) mainly depends on the absorber front temperature level, which is well predicted by the model.

Commentary by Dr. Valentin Fuster
2016;():V001T10A002. doi:10.1115/ES2016-59239.

Hydrogen production from water via efficient solar based photocatalytic or photoelectrochemical processes could play a major role in the energy regimes of the future. Here, intermittent solar energy is converted into the promising energy vector hydrogen for later carbon free use on demand. Although much effort has been made in the last years photocatalytic/photoelectrochemical systems with acceptable solar-to-hydrogen-efficiency for economic operation could not be introduced, yet. Within the project DuaSol simultaneous hydrogen generation and water treatment in a photoelectrochemical tandem cell is investigated as a potentially economic process. Organic contaminants are oxidised by interaction with photo-generated electron holes at the photoanode. Produced protons approach the photocathode to react with photo-generated electrons to form hydrogen. Experiments with photocatalytic systems employing DLR’s 2-axis tracking modified linear Fresnel solar concentrator SoCRatus (Solar Concentrator with a Rectangular Flat Focus) were carried out in order to set a reference for the further experimental assessment. Diverse photocatalysts based on titanium dioxide (TiO2) and tin niobate (SnNb2O6) were tested in a planar suspension reactor with two parallel reaction chambers irradiated in the focal plane of the SoCRatus. The evolution of hydrogen was measured and correlated to the overall solar input and to spectral quantities. Three temperature levels, mostly 25°C, 37.5°C, and 50°C, were considered and maintained during the experiments in order to study temperature related effects. Methanol as a sacrificial reagent or rather a model substance for organic contaminants formed part of the suspension with a volume fraction of 10% at 20°C. As expected regarding the band gaps of the considered TiO2 based photocatalysts the hydrogen output is predominately affected by the applied UV portion. The UV fraction of solar light varies significantly in the course of a day and coherently also the production of hydrogen. Hydrogen was generated at rates as high as 7386 μmol/h. Regarding the SnNb2O6 based photocatalysts the generation of hydrogen rather corresponds with the irradiance in the visible range. The solar-to-hydrogen efficiency as well as the photon efficiency in different spectral ranges could be calculated. In addition an extensive analysis of the uncertainty of experimental results was conducted. It could be confirmed that the SoCRatus is an excellent platform for the experimental assessment of photocatalytic / photoelectro-chemical systems under practical conditions.

Commentary by Dr. Valentin Fuster

Sustainable Building Energy Systems

2016;():V001T11A001. doi:10.1115/ES2016-59091.

Energy efficiency programs implemented by utilities in the U.S. have rendered savings costing on average $0.03/kWh [1]. This cost is still well below energy generation costs. However, as the lowest cost energy efficiency measures are adopted, the cost effectiveness of further investment declines. Thus, there is a need to develop large-scale and relatively inexpensive energy auditing techniques to more efficiently find opportunities for savings. Currently, on-site building energy audits process are expensive, in the range of US$0.12/sf – $0.53/sf, and there is an insufficient number of professionals to perform the audits. Here we present research that addresses at community-wide scales the characterization of building envelope thermal characteristics via drive-by and fly-over GPS linked thermal imaging. A central question drives this research: Can single point-in-time thermal images be used to infer R-values and thermal capacitances of walls and roofs? Previous efforts to use thermal images to estimate R-values have been limited to stable exterior weather conditions. The approach posed here is based upon the development of a dynamic model of a building envelope component with unknown R-value and thermal capacitance. The weather conditions prior to the thermal image are used as inputs to the model. The model is solved to determine the exterior surface temperature, ultimately predicted the temperature at the thermal measurement time. The model R-value and thermal capacitance are tuned to force the error between the predicted surface temperature and the measured surface temperature from thermal imaging to be near zero. The results show that this methodology is capable of accurately estimating envelope thermal characteristics over a realistic spectrum of envelope R-values and thermal capacitance present in buildings nationally. With an assumed thermal image accuracy, thermal characteristics are predicted with a maximum error of respectively 20% and 14% for high and low R-values when the standard deviation of outside temperature over the previous 48 hours is as much as 5°C. Experimental validation on a test facility with variable surface materials was attempted under variable weather conditions, e.g., where the outdoor air temperature experiences varying fluctuations prior to imaging. The experimental validation realized errors less than 20% in predicting the R-value even when the standard deviation of outdoor temperature over the 48 hours prior to a measurement was approximately 5°C.

Commentary by Dr. Valentin Fuster
2016;():V001T11A002. doi:10.1115/ES2016-59130.

In this study, the performance of the basic adsorption cooling system based on a metal organic framework, HKUST-1, is investigated and compared with that of a zeolite based system. The optimal regeneration temperature to maximize the COP of the HKUST-1-water based basic adsorption cycle is presented. The solar-thermal powered adsorption chiller model running on the HKUST-1-water based basic adsorption cycle is developed and integrated into a building model (two-story house located in Kingsville, Texas) in TRNSYS. The yearly performance of the integrated system is simulated by employing the latest typical meteorological year data (TMY3) for Kingsville, Texas. The solar fraction of the solar-assisted adsorption cooling system is also presented.

Commentary by Dr. Valentin Fuster
2016;():V001T11A003. doi:10.1115/ES2016-59133.

Membrane based liquid desiccant dehumidifier and regenerator system have recently gained much attention in liquid desiccant air-conditioning (LDAC) system due to their merit of zero contamination or carryover and resistance to corrosion. A typical system for the LDAC application will consist of a number of stages depending on the capacity of the LDAC system. The multi-effect design allows energy recovery to be achieved to reduce the overall thermal energy consumption. The objective of this study was to test and evaluate the effectiveness and performance of solar powered multi-effect distillation system with desiccant salt solution.

Design Expert was used to characterize the output of regenerator system and optimize overall design using sets of experiment test data. The optimized working zone for performance ratio for different feed flow rate and hot water temperature has been derived. It was found that the optimized zone for LiCl inlet concentration 31.71% was representing performance ratio of 0.5 if operated at feed flow rate range of 32 L/min to 60 L/min and hot water temperature of 54°C to 67°C and optimized zone for LiCl inlet concentration 37.74% was representing performance ratio of 0.5 if operated at feed flow rate range of 40 L/min to 50 L/min and hot water temperature of 59°C to 67°C.

Commentary by Dr. Valentin Fuster
2016;():V001T11A004. doi:10.1115/ES2016-59153.

Major metropolitan centers experience challenges during management of peak electrical loads, typically occurring during extreme summer events. These peak loads expose the reliability of the electrical grid and customers may incur in additional charges for peak load management in regulated demand-response markets. This opens the need for the development of analytical tools that can inform building managers and utilities about near future conditions so they are better able to avoid peak demand charges, reducing building operational costs. In this article, we report on a tool and methodology to forecast peak loads at the City Scale using New York City (NYC) as a test case. The city of New York experiences peak electric demand loads that reach up to 11 GW during the summertime, and are projected to increase to over 12 GW by 2025, as reported by the New York Independent System Operator (NYISO). The forecast is based on the Weather Research and Forecast model version 3.5, coupled with a building environment parameterization and building energy model. Urban morphology parameters are assimilated from the New York Primary Land Use Tax Lot Output (PLUTO), while the weather component of the model is initialized daily from the North American Mesoscale (NAM) model. A city-scale analysis is centered in the summer months of June-July 2015 which included an extreme heat event (i.e. heat wave). The 24-hr city-scale weather and energy forecasts show good agreement with the archived data from both weather stations records and energy records by NYISO.

Commentary by Dr. Valentin Fuster
2016;():V001T11A005. doi:10.1115/ES2016-59180.

This paper describes the application of ‘passive house’ design principles to greenhouses, in order to provide the required thermal environment for fish and plant growth while eliminating the need for conventional cooling and heating systems. To do so, an experimental energy-efficient greenhouse with water-filled tanks that mimic an aquaponic system was designed and constructed using the ‘passive house’ design principles. The greenhouse was extensively instrumented and resulting data were used to verify and calibrate a TRNSYS dynamic simulation model of the greenhouse. The calibrated simulation model was utilized to design commercial-scale greenhouses with aquaponic systems in multiple climates. After relatively minor design and control modifications, the simulations indicate that these designs can provide the required thermal environment for fish and plant growth, while eliminating the need for conventional cooling and heating systems. The work demonstrates that the passive house standard can be applied to improve conventional greenhouse energy efficiency, and that it can be easily adapted to provide excellent performance in diverse climates.

Commentary by Dr. Valentin Fuster
2016;():V001T11A006. doi:10.1115/ES2016-59253.

A rechargeable personal air-conditioning (RPAC) device was developed to provide an improved thermal comfort level for individuals in inadequately cooled environments. This device is a battery powered air-conditioning system with the phase change material (PCM) for heat storage. The condenser heat is stored in the PCM during the cooling operation and is discharged while the battery is charged by using the vapor compression cycle as a thermosiphon loop. The conditioned air is discharged towards a single person through adjustable nozzle. The main focus of the current research was on the development of the cooling system. A 100 W cooling capacity prototype was designed, built, and tested. The cooling capacity of the vapor compression cycle measured was 165.6 W. The PCM was recharged in nearly 8 hours under thermosiphon mode. When this device is used in the controlled built environment, the thermostat setting can be increased so that building air conditioning energy can be saved by about 5–10%.

Commentary by Dr. Valentin Fuster
2016;():V001T11A007. doi:10.1115/ES2016-59255.

This study evaluated the building cooling capacity of sky radiation, which was previously identified to have the greatest cooling potential among common ambient sources for climates across the US. [Robinson, et al. 2013b]. A heat pipe augmented sky radiator system was simulated by a thermal network with nine nodes, representing a thin polyethylene cover, white (ZnO) painted radiator plate [Duffie & Beckman 2013], condenser and evaporator ends of the heat pipe, thermal storage fluid (water), tank wall, room, sky and ambient air. Heat transfer between nodes included solar flux and sky radiation to cover and plate, wind convection and radiation from cover to ambient, radiation from plate to ambient, natural convection and radiation from plate to cover, conduction from plate to condenser or, two-phase heat transfer from evaporator to condenser, natural convection from evaporator to water and from water to tank wall, natural convection and radiation from tank wall to room, and overall heat loss from room to ambient. Nodal temperatures were simultaneously solved as functions of time using Typical Meteorological Year (TMY3) weather data. Auxiliary cooling was applied as needed to limit room temperature to a maximum of 23.9°C. For this initial investigation, a moderate climate (Louisville, KY) was used to evaluate the effects of radiator orientation, thermal storage capacity and cooling load to radiator area ratio, LRR. Louisville and two challenging climates (Miami, FL and New Orleans, LA) were then used to evaluate five cover configurations — zero, one and two covers with unconstrained temperature, and zero and one cover with temperature limited to the dew point of ambient air to simulate condensation on the cover. Results were compared to a Louisville baseline with LRR = 10 W/m2K, horizontal radiator and one cover with constrained temperature, which provided an annual sky fraction (fraction of cooling load provided by sky radiation) of 0.861. A decrease to 0.857 was found for an increase in radiator slope to 20°, and a drop to 0.833 for 53° slope (latitude + 15°, a typical slope for solar heating). These drops were associated with increases in average radiator temperature by 0.2°C for 20° and 1.5°C for 53°. A 25% decrease in storage capacity caused a decrease in sky fraction to 0.854. Sky fractions were 0.727 and 0.963 for LRR of 20 and 5, respectively. Sky fractions for the baseline system in Miami and New Orleans were 0.505 and 0.603, respectively. In all three climates, performance was little affected by constraining the cover temperature and by adding a second cover. These results confirm the potential for passive cooling of buildings by radiation to the sky. Climate, LRR and thermal storage capacity had strong effects on performance, while the cover configuration did not. Radiator slope had a surprisingly small impact, considering that the view factor to the sky at 53° tilt is less than 0.5.

Commentary by Dr. Valentin Fuster
2016;():V001T11A008. doi:10.1115/ES2016-59267.

In order to reduce the quantity of CO2 emissions economically, it is important to construct a Smart Community which is expected to be one of the solutions. In a Smart Community, energy supply and demand system is developing to manage with ICT (Information and Communication Technology) to utilize energy efficiently and increase the amount of renewable energy. In one of the systems, “Photovoltaic power generator (hereinafter referred to as PV) & Electric Vehicle (hereinafter referred to as EV) Smart System” has been developed.

In the “PV & EV Smart System”, PV power is charged directly to the EV battery, and then the charged PV power is consumed by running and air-conditioning energy of a car and supplied to a home. This system is able to reduce the quantity of CO2 emissions with high economic efficiency. In order to expand the system, it is necessary to spread EV. So, it should solve the issues of short driving distance, the high cost of storage battery and the risk of dead battery. Therefore, the authors have proposed an advanced EV such as AI-EV (Air-conditioner Integrated Electric Vehicle). AI-EV has a novel hybrid system which drives the air-conditioning system and generates electric power in the case of a low air-conditioning load through the use of a small-engine. PV power can not only reduce car fuels but also replace with gas and liquid fuels which are used at a home, causing the huge effect of reducing CO2 emissions as the whole system.

In this paper, a novel energy system which is integrated with solar power, advanced electric vehicle and CO2 heat pump water heater as home heat pumps has been proposed. A mathematical simulation model which evaluates for the PV power generation, AI-EV energy consumption and home heat pumps has been developed. CO2 emissions and economic efficiency are calculated and compared with those of the conventional system.

As the result, the novel energy system is able to reduce more than 30% of the quantity of CO2 emissions in comparison with the conventional system as the whole system, and the system can reduce about 60% of the quantity of CO2 emissions in comparison with the conventional system as a home system. The economic efficiency is evaluated by more than 6.0% of IRR (Internal Rate of Return) without some subsidies when the legal service life of the depreciation equipment is assumed 14 years. Therefore, the novel energy system can be widely spread in the future.

Commentary by Dr. Valentin Fuster
2016;():V001T11A009. doi:10.1115/ES2016-59291.

A district cooling system (DCS) is a system that distributes thermal energy through chilled water from a central source to residential, commercial, or industrial consumers, designated to air conditioning purposes. It is one of the most important part of a heating, ventilation, air conditioning and refrigeration systems (HVAC), because a DCS is composed of: Cooling towers, central chiller plant, water distribution systems and clusters of consumer buildings. This research is focused on the central chiller plant, due to it accounts for a substantial portion of the total energy consume of DCS and HVAC systems. The performance of central chiller plant is often affected by multiple faults which could be caused during installation or developed in routine operation. These non-optimal conditions and faults may cause 20–30% waste of energy consumption of HVAC&R systems. Automated fault detection and diagnosis (AFDD) tools have potential to detect an incipient fault and help to reduce undesirable conditions and energy consumption, and optimize the facility maintenance. We propose an online data driven fault detection strategy for district cooling system. The main objective is to develop an automated fault detection tool based on historical process data, which can be applied in transient operation. The proposed hybrid strategy is based on unsupervised and supervised learning techniques, and multivariate statistic techniques. Its aim is to identify the operating states of the chiller and evaluate the fault occurrence depending of its current operating state. This strategy uses the K-means clustering method, Naive Bayes classifier and Principal Component Analysis (PCA). The developed strategy was evaluated using the performance data of a 90-ton water-cooled centrifugal chiller (ASHRAE RP-1043) and also evaluated using a dynamic model of a chiller (Simscape™.) under similar conditions. The results show the advantages of novel early fault detection technique compared to Conventional PCA method in terms of sensitivity to faults occurrence and reduction of missed detection rate.

Topics: Flaw detection
Commentary by Dr. Valentin Fuster
2016;():V001T11A010. doi:10.1115/ES2016-59307.

Achieving energy efficiency in buildings is an important factor in developed and as well in developing countries in order to meet its energy demand. Over the past few years, a number of reports have been emerged stating that the buildings sectors are responsible for approximately 31% of global final energy demand. Buildings account for 35% of total final energy consumption in India and building energy consumption is growing about 8% per years. Final energy demand in Indian building sector will grow up-to five times by the end of this century, driven by rapid income and population growth. Hospitals are institutions for the care of people with health problems and are usually functional 24hrs a day, all year around, which demands a lot of energy. Health sector is one of the largest and fastest growing sectors in India. By 2020, it is expected to become a $ 280 billion industry. In India hospitals contribute 23% of total energy consumption and the hospital building growth rate 12–15% in last decade. The World Health Organization estimated that India need 80,000 additional hospital beds every year to meet the demands of India’s population. The aim of this study is to assess the energy demand, energy savings & reduced greenhouse gas emissions by increasing the energy efficiency using advanced retrofitting. Bottom-Up Energy Analysis System (BUENAS) is an end use energy demand projection model for Hospital buildings in India, to normalize the assessment of energy-saving models also going to fill the gap in energy demand reduction by energy system modeling and decomposition analysis. Energy efficiency retrofitting of existing buildings plays a major role in developing country like India in order improve its energy security and minimizing the greenhouse gases. The positive effects of retrofitting of energy efficiency and need the policies and target base proposal for government intention to achieve the potential for energy efficiency are discussed.

Commentary by Dr. Valentin Fuster
2016;():V001T11A011. doi:10.1115/ES2016-59313.

There is rich solar energy in Taiwan, it also has a great developing potential for solar applications. Solar hot water is able to supply the domestic hot water, the heating load, and the driving energy for absorption cooing. In this paper, a computer simulation program for a multi-purpose solar hot water system providing hot water, winter heating and summer air-conditioning is established by TRNSYS program. Simulation study is done with varying parameters including collector area, storage capacity and type of collector (flat plate and evacuated tube). In order to study the system performance in Taiwan, system simulations are made under the climate data of three representative cities (Taipei in north, Taichung in central, and Kaohsiung in southern) of Taiwan. The results of the present study can provide important reference for the development of the multi-purpose solar hot water system.

Commentary by Dr. Valentin Fuster
2016;():V001T11A012. doi:10.1115/ES2016-59391.

Reducing global emissions and meeting the electricity generation needs of urban areas are compelling energy issues. Rooftop and small-scale photovoltaic (PV) technology is a quickly growing sector of the distributed generation market. The array size chosen for a PV installation is one of the main factors affecting its ability to meet a building’s electrical needs and reduce its operational emissions.

The rooftop area available for placement of PV can be a constraint on the optimization of PV array size. If the optimal array area for a specific building is larger than the area available on the rooftop, optimization using demand-matching methods is not necessary.

A new parameter EUI-R has been introduced to describe the building’s annual electrical demand with respect to the building rooftop area. It is a decision-making tool presented to help a system designer choose whether to employ an optimization method or not in selecting a PV system. The EUI-R depends on 2 general parameters, building electric demand and building rooftop area, that should be easily accessible for any system designer. This paper presents an extended study of EUI-R applied to 10 commercial building types in 3 different climate zones throughout the U.S. These cities are characterized by different latitudes and varying amounts of available solar radiation. The results show a linear dependency between optimal PV size obtained with a simple demand-matching algorithm, and building rooftop area, applicable to any building type. Any distributed energy technology serving a single building should be sized based on the specific conditions unique to the building, including electric demand and physical space available.

Commentary by Dr. Valentin Fuster
2016;():V001T11A013. doi:10.1115/ES2016-59593.

Buildings are widely recognised as key contributors to global energy use and emissions. Approximately 50% of the energy consumption of the non-domestic buildings is due to Heating Ventilation and Air-Conditioning (HVAC) systems. Therefore, there is great potential in improving the energy performance of buildings, by investigating the deployment of low-carbon HVAC technologies. HVAC system selection is usually performed in early design stages, when there is high uncertainty associated with the system’s requirements. To deal with these uncertainties, Global Sensitivity Analysis (GSA) can be deployed. GSA can systematically identify the most important variables, in terms of their impact on system performance. This study considers the usefulness of GSA in designing HVAC systems with an office building case study. GSA identifies the heat pump and heat recovery efficiencies as the most significant uncertain parameters. These, account for more than 90% of the observed variation in the energy consumption. Additionally, the results reveal that by selecting a heat pump capacity at 80% of the potential annual peak load point estimate, there is 95% probability for the system to satisfy the peak demand at any given hour. The analysis demonstrates the potential of GSA in informing the design of novel HVAC and power generation technologies.

Commentary by Dr. Valentin Fuster
2016;():V001T11A014. doi:10.1115/ES2016-59663.

In European countries seasonal thermal energy storage is an emergent task due to availability of solar energy in summer and thermal energy demand in winter. In this study the performance of an uninsulated buried storage tank is analyzed. Summer temperatures reached 45 °C in the storage tank and 22 °C in the soil, 1 m from the tank shell. Wintertime temperature of the storage tank dropped to 8 °C, near the freezing limit of the heat pump, and soil cooled down to 9 °C. While in wintertime heat transfer from earth to water was the limiting factor, a summertime temperature difference of more than 20 °C allowed enough energy transport to charge the soil storage system. An analytical model showed that more than 50% of the solar energy stored could be recovered by this application.

Topics: Solar energy , Storage
Commentary by Dr. Valentin Fuster
2016;():V001T11A015. doi:10.1115/ES2016-59667.

Data center cooling systems have long been burdened by high levels of redundancy requirements, resulting in inefficient system designs to satisfy a risk-adverse operating environment. As attitudes, technologies, and sustainability awareness change within the industry, data centers are beginning to realize higher levels of energy efficiency without sacrificing operational security. By exploiting the increased temperature and humidity tolerances of the information technology equipment (ITE), data center mechanical systems can leverage ambient conditions to operate in economization mode for increased times during the year. Economization provides one of the largest methodologies for data centers to reduce their energy consumption and carbon footprint. As outside air temperatures and conditions become more favorable for cooling the data center, mechanical cooling through vapor-compression cycles is reduced or entirely eliminated. One favorable method for utilizing low outside air temperatures without sacrificing indoor air quality is through deploying rotary heat wheels to transfer heat between the data center return air and outside air without introducing outside air into the white space. A metal corrugated wheel is rotated through two opposing airstreams with varying thermal gradients to provide a net cooling effect at significantly reduced electrical energy over traditional mechanical cooling topologies. To further extend the impacts of economization, data centers are also able to significantly raise operating temperatures beyond what is traditionally found in comfort cooling applications. The increase in the dry bulb temperature provided to the inlet of the information technology equipment, as well as an elevated temperature rise across the equipment significantly reduces the energy use within a data center.

Commentary by Dr. Valentin Fuster

Sustainable Infrastructure and Transportation

2016;():V001T12A001. doi:10.1115/ES2016-59086.

When buildings of various use-types are served by a district energy system, many societal benefits occur, including improved capacity utilization, reduced energy use, and more cost-effective redundancy. In addition, a central system may benefit financially from commodity leveraging, utility incentives and cogeneration. Energy conversion and transport efficiency for steam and hot water are explored and presented. System optimization curves, including generation and distribution, are presented along with long-term financial comparisons to decentralized systems.

Commentary by Dr. Valentin Fuster
2016;():V001T12A002. doi:10.1115/ES2016-59629.

Although hydrogen has one of the highest specific energies, its energy density in terms of volume is very poor compared to liquid fuels. Thus to achieve attractive energy density for hydrogen, either high pressure compression or a storage method is needed. For onboard (vehicles) hydrogen storage, up to 700 bars are needed for commercial fuel cell vehicles. This creates extreme requirements for material strength and thus safety concerns. A new metal-organic framework (MOF-5) was selected as the adsorbent for H2 storage, as it provides promising storage capacity and is commercially available. Under the same H2 storage capacity and tank volume, the adsorption system is expected several folds reduction in pressure. Under the current study, a unique Modular Adsorbing Tank Insert (MATI) design paired with conduction enhanced compressed MOF-5 beds was introduced and experimentally compared for thermal performance, which determines system charge and discharge cycle times.

Commentary by Dr. Valentin Fuster

Thermodynamic Analysis of Energy Systems

2016;():V001T13A001. doi:10.1115/ES2016-59084.

The guayule (Parthenium argentatum) plant is a source of natural rubber and a possible high-energy biofuel. Herein guayule bagasse, the residual biomass after latex extraction, which accounts for 90% of the processed plant material, is modeled in a fast pyrolysis biorefining process. The simulation uses PRO/II® software and is based on data and processes used successfully in a bench scale facility. The unique 200-ton per day plant includes fast pyrolysis utilizing the tail gas reactive process followed by atmospheric separation, hydrodeoxygenation and final product separation, resulting in products similar to traditional fuels, i.e., gasoline, jet fuel and diesel. Approximately 10% of the biomass is converted to liquid fuels with 10% of this converted to gasoline, 34% jet fuel and 56 % diesel. These yields are compared to alternative feedstock and methods. The simulation results are utilized in an exergetic assessment. The depletion of exergy from its natural state (cumulative exergy demand, CExD) is considered as a measure of sustainability of the refining process. Breeding factors, measures of exergy production (the ratio of chemical exergy of the output products to the process exergy inputs), are determined. Results show, for the entire biorefining process, favorable breeding factors can possibly exceed 10, thus suggesting a favorable method of exergy production.

Commentary by Dr. Valentin Fuster
2016;():V001T13A002. doi:10.1115/ES2016-59209.

The fresh water is the essence of life and its scarcity is the most threatening concern for mankind. To alleviate the worries of the existing and approaching fresh water crisis, the answer for water sustainability may lie in developing the decentralized small-scale water desalination system. Solar humidification-dehumidification (HDH) is a carrier gas based thermal technique that is ideal for a small-scale decentralized water desalination system. An innovative design approach is to use the bubble column humidifier to enhance the performance of the HDH water desalination system. Therefore, a novel multi-stage stepped bubble column humidifier is proposed that is operated through solar thermal energy as the main source of energy input. The study addresses the relation between the pressure drop variations with varying water column height at different air superficial velocities. Findings revealed that the water column height and air superficial velocity should be optimized according to the geometric features of the perforated plate in order to achieve a higher humidifier performance with a lower pressure drop. The day round performance of the humidifier is investigated in single stage, two stage, and three stage configurations. Findings show that the average day round absolute humidity at the exit of the humidifier is increased by 9 % in two-stage and 23 % in three-stage configurations compared to the single stage humidifier. One major advantages of this proposed humidifier is its ability to have a direct solar thermal heating. Subsequently, it can be located in remote areas.

Commentary by Dr. Valentin Fuster
2016;():V001T13A003. doi:10.1115/ES2016-59211.

Solar thermal energy is considered one of the most promising renewable energy resources, especially for high intensive solar radiation locations, such as Saudi Arabia. Therefore, there is a need to assess the performance of one potential dominant solar thermal energy technology that can be applied in Saudi Arabia, which is Solar Chimney Power Plant (SCPP). SCPP is guided through natural draft utilizing solar radiant energy to impart ascending thrust to the flow of air and therefore, transforming the radiant energy to run the turbine. This paper presents the exergy analysis of the assumed model of the SCPP and presents its performance for Dhahran, Saudi Arabia, as an illustrative of the exergy model developed. The modeling was validated against published data. The tower height is 195 m and the collector diameter is 240 m. The tower can produce, on average, around 123kW during daytime and has, on average, air mass flow rate of around 160 kg/s. The exergetic efficiency was found to be around 0.45%.

Commentary by Dr. Valentin Fuster
2016;():V001T13A004. doi:10.1115/ES2016-59234.

Heating and cooling is a prime need for various day to day operations and one of the most basic requirements is space conditioning. A huge amount of energy all across the globe is being used for this purpose using various conventional & non-conventional energy based resources. But environmental problems, fast depletion nature and high prices associated with the use of conventional energy sources is becoming a big problem, due to which promotion of non-conventional energy sources becomes important. The use of an in-ground heat exchanger is a unique technique for space conditioning with reduced energy consumption. A lot of research and studies have been done on the design of such systems. This paper presents a study based on the CFD modelling and simulation to analyze the effect on the effective performance of the system by varying the geometry of ducts and using the extended surface to increase the heat transfer rate. Also, a comparative study of performance of earth tube heat exchanger for different cross section of ducts is also presented.

Commentary by Dr. Valentin Fuster
2016;():V001T13A005. doi:10.1115/ES2016-59272.

Absorption Power Cycles (APCs) provide an interesting field within power cycles. The multicomponent mixture with variable temperature across boiling is employed as a working fluid. This has a potential for decreasing exergy loss associated with heat transfer during phase change processes (boiling and condensation). Absorption process has also an effect of lowering exhaust pressure of a turbine. The APCs hold a potential for heat recovery applications at very low temperatures, where constant temperature of boiling and condensation largely limits performance and economic effectiveness of Organic Rankine cycles (ORCs). Theoretical calculations show superiority of APC over extensive range of considered ORC working fluid. The advantage of APC further increases when air cooled condenser needs to be used instead of wet cooling tower. With the same boundary conditions for all cycles the APC provides higher utilization efficiency and power output at source temperatures below approximately 120 °C, for temperatures as low as 60 °C the net power output can be surpassed even more than three times.

The proposed APC employs aqueous solution of salts considered generally for absorption cooling (Lithium Bromide, Lithium Chloride, Calcium Chloride) as a working fluid. Unlike ammonia used in mixture with water in Kalina APC or often ORC working fluids, used salts are non-toxic, environmentally friendly and pure water in expander simplifies its design. After summary of theoretical research from thermodynamics point of view are discussed principles, aspects and issues for design of single components of the cycle. Results of sizing are presented on two examples with 100 °C heat source. First one is 20 kWe unit using hot air as a heat source and air cooled condenser, second one is 500 kWe unit with heat source being pressurized water and using wet cooling tower heat rejection. Results show possibility of building relatively efficient system for even small power output with turbine isentropic efficiency nearly 80 % for the 20 kWe unit, but relatively large heat exchangers.

Commentary by Dr. Valentin Fuster
2016;():V001T13A006. doi:10.1115/ES2016-59369.

Fixed bed and rotatory desiccant systems have been widely studied and used for dehumidification; they suffer from decreasing sorption capacity as the desiccant’s temperature increases due to the released heat of adsorption. The desiccant coated heat exchangers (DCHX) overcome this limitation. Such heat exchangers are able to deliver combined heat and mass transfer between the process air and the working fluid. The process air can be cooled and dehumidified simultaneously by pumping cooling water/refrigerant in the DCHX. The DCHX has to be heated cyclically to regenerate the desiccant material. This paper presents a review on the studies conducted on air-to-liquid DCHX. It summarizes various modeling approaches used to simulate the performance of DCHX as well as the experimental studies conducted to validate these models. It also reviews the current and potential applications of these heat exchangers. Current work in this field consists of experiments conducted on the DCHX as standalone equipment (i.e. component level) as well as an integrated component into cooling and dehumidification systems (system level). The integration of the DCHX in such systems was found to improve the COP, leading to energy savings.

Topics: Heat exchangers
Commentary by Dr. Valentin Fuster
2016;():V001T13A007. doi:10.1115/ES2016-59383.

This paper presents a dynamic model of a single-stage LiBr-H2O absorption chiller. A numerical model has been developed based on mass and energy balance equations and heat transfer equations. The model is developed using MATLAB program and the system of non-linear ordinary differential equation is solved using the 4th-order Runge-Kutta method. The model is validated with experimental results from pertained literature. The results show that the maximum relative error is found when comparing the dynamic model predicted chilled water outlet temperature to experimental data, which is around 9%. The effect of the inlet hot water temperature on the hot, cooling and chilled water outlet temperatures, cooling capacity and coefficient of performance (COP) are also studied. The results show that as the hot water outlet temperature increases, the outlet temperatures of cooling and chilled water slightly change. Moreover, the cooling capacity increases and the COP slight decreases as the hot water temperature increases.

Commentary by Dr. Valentin Fuster
2016;():V001T13A008. doi:10.1115/ES2016-59467.

Two significant goals in solar plant operation are lower cost and higher efficiencies. This is both for general competitiveness of solar technology in the energy industry, and also to meet the US DOE Sunshot Initiative Concentrating Solar Power (CSP) cost goals [1]. We present here an investigation on the effects of adding a bottoming steam power cycle to a solar-fossil hybrid CSP plant based on a Small Particle Heat Exchange Receiver (SPHER) driving a gas turbine as the primary cycle. Due to the high operating temperature of the SPHER being considered (over 1000 Celsius), the exhaust air from the primary Brayton cycle still contains a tremendous amount of exergy. This exergy of the gas flow can be captured in a heat recovery steam generator (HRSG), to generate superheated steam and run a bottoming Rankine cycle, in a combined cycle gas turbine (CCGT) system. A wide range of cases were run to explore options for maximizing both power and efficiency from the proposed CSP CCGT plant. Due to the generalized nature of the bottoming cycle modeling, and the varying nature of solar power, special consideration had to be given to the behavior of the heat exchanger and Rankine cycle in off-design scenarios.

Variable guide vanes (VGVs), which can control the mass flow rate through the gas turbine system, have been found to be an effective tool in providing operational flexibility to address the variable nature of solar input. The effect VGVs and the operating range associated with them are presented. Strategies for meeting a minimum solar share are also explored. Trends with respect to the change in variable guide vane angle are discussed, as well as the response of the HRSG and bottoming Rankine cycle in response to changes in the gas mass flow rate and temperature. System efficiencies in the range of 50% were found to result from this plant configuration. However, a combustor inlet temperature (CIT) limit lower than a turbine inlet temperature (TIT) limit leads two distinct Modes of operation, with a sharp drop in both plant efficiency and power occurring when the air flow through the receiver exceeded the (CIT) limit, and as a result would have to bypass the combustor entirely and enter the turbine at a significantly lower temperature than nominal. Until that limit is completely eliminated through material or design improvements, this drawback can be addressed through strategic use of the variable guide vanes. Optimal operational strategy is ultimately decided by economics, plant objectives, or other market incentives.

Commentary by Dr. Valentin Fuster
2016;():V001T13A009. doi:10.1115/ES2016-59524.

Water desalination and air conditioning consumes huge amount of energy that mostly come from fossil fuels, which produces harmful emissions detrimental to the environment. This work is concerned with the use of a new hybrid cooling and water desalination system driven by solar thermal energy. The system primarily consists of an evacuated tube solar collector, LiBr absorption chiller, and a humidification-dehumidification (HDH) unit. Seawater is used to cool the condenser and absorber of the chiller as well as the condenser of the HDH unit. The heat rejected by the absorber is used to drive the HDH unit. Thermodynamic model of the system has been formulated and simulated using engineering equation solver (EES) software. The results show that the coefficient of performance (COP) of the chiller nearly remain constant with increase in seawater temperature at the absorber inlet. The average COP of the chiller is found to be 0.76. The hybrid system efficiency increases with increase in the seawater temperature mainly due the effect of latent heat of water condensation. The rate of fresh water production increases with increase in the seawater inlet temperature. This resulted in a higher outlet temperature at the absorber exit, leading to a higher energy input to the HDH unit. Gained output ratio (GOR) increases with increase in seawater temperature. This is due to the direct proportionality of the GOR to the amount of fresh water produced. The results also revealed that increasing the flow rate of seawater causes the decrease in the fresh water production due to the corresponding decrease in the temperature of the seawater.

Topics: Cooling , Solar energy
Commentary by Dr. Valentin Fuster
2016;():V001T13A010. doi:10.1115/ES2016-59680.

In this paper a thermoeconomic and exergy analysis of a steam power plant located at Villa de Reyes, México is presented. This study is focused on the analysis on partial load of this plant. According to the steam power plant operation manual this plant is able to operate at 25%, 50%, 75% and 100% of the total load installed, and some design parameters are established for this operation loads. Nevertheless during this study it was observed that this parameters and operation loads conditions are not the most efficient from the energetic and exergetic point of view, and also, the values of the thermal parameters used for these operation loads were not the optimum. In this context the objective of this research was to design a model for the power plant simulation in order to determine the best design parameters and operation loads conditions for this particular facility. First of all the model was validated, with the information of the operation manual of the steam generator. Once the model was validated, it was achieved the thermal, exergetic and thermoeconomic analysis. As a result it was observed that the best operation load conditions are at 100%, 98.4%, 93.3% and 75.6%. Also some optimal values of air-gas relation, extraction pressure and drum pressure were found. It was observed that an energetic efficiency up to 35.5% and exergetic efficiency up to 29% may be achieved. Finally it was achieved the thermoeconomic analysis in order to determine the cost of the energetic and exergetic loses and identify the elements that produce the higher irreversibility.

Commentary by Dr. Valentin Fuster

Wind Energy Systems and Technologies

2016;():V001T14A001. doi:10.1115/ES2016-59151.

The rise of energy prices, concerns over climate change and geopolitical issues have brought special attention to renewable sources of energy and wind energy in particular. Based on NREL projections, the United States has more than 32,000 TWh of onshore and 17,000 TWh of offshore potential for wind power generation, which is far beyond its 11,000 TWh of current annual electricity consumption. However, there are a number of efficiency challenges that must be overcome in order to turn this potential into actual production. One area that can potentially improve the energy production of wind turbines is the correction of yaw error. Yaw error (also referred to as yaw angle or yaw misalignment) is the angle between the turbine’s rotor and the wind direction. A yaw error reduces turbine’s power production at wind speeds below the rated speed.

Besides impacting the power producing ability of a turbine, yaw error also affects the reliability of critical subsystems in wind turbines. Variation in yaw error (at any wind speed and not only below the rated speed) affects the loads on the components and the subsequent mechanical stresses. These mechanical stresses change the damage accumulation for components and sub-assemblies, which ultimately affects their reliability. About 17 to 28% of wind project costs attribute to O&M costs, which are directly affected by the reliability.

In this study, we investigate the effects of yaw error on the reliability of blades by performing load and stress analysis for various yaw errors. We then use the results of these analyses to adjust the Weibull parameters used for predicting the failure time of blades. Finally, we will use a stochastic cost model to show how correcting the yaw error can avoid maintenance costs in wind farms.

Commentary by Dr. Valentin Fuster
2016;():V001T14A002. doi:10.1115/ES2016-59539.

Offshore wind farms are presently facing numerous technical challenges that are affecting their viability. High failure rates of expensive nacelle-based electronics and gearboxes are particularly problematic. On-going research is investigating the possibility of shifting to a seawater-based hydraulic power transmission, whereby wind turbines pressurise seawater that is transmitted across a high-pressure pipeline network. A 9-turbine hydraulic wind farm with three different configurations is simulated in the present work and a previously developed method for open-loop pressure control of a single turbine has been adapted for this multiple-turbine scenario. A conceptual quasi-constant-pressure accumulator is also included in the model. This system is directly integrated within each hydraulic wind turbine and it allows the output power from the wind farm to be scheduled on an hourly basis. The shift in control methodology when integrating storage is illustrated in the present work. Simulation results indicate a strong relationship between hydraulic performance attributes and the specific wind turbine array layout. The beneficial effects of storage can also be observed, particularly in smoothing the output power and rendering it more useable. Finally, the energy yields from 24-hour simulations of the 9-turbine wind farms are calculated. Integrated storage leads to a slight increase in yield since it eliminates bursts of high flow, which induce higher frictional losses in the pipeline network.

Commentary by Dr. Valentin Fuster
2016;():V001T14A003. doi:10.1115/ES2016-59548.

Fossil fuels have been a means of energy source since a long time, and have tended to the needs of the large global population. These conventional sources are bound to deplete in the near future and hence there is a need for producing energy from renewable energy sources like solar, wind, geothermal, tidal etc. Technologies involving renewable energy are a growing subject of concern. Further, the problem is also one of excessive pollution caused by conventional sources of energy and their impact on the environment. In particular, one of the main sources of pollution is harmful gases emitting out of automobiles. Wind energy is one among the renewable energy sources which is implemented in large scale energy production to supplement growing domestic energy needs. Significant amount of research has been done in this field to harness energy to power household and other amenities using wind farms. The aim of this project is to come up with a low cost solution for wind energy harvesting on moving vehicles. The purpose of this study is to consider the use of wind energy along with conventional energy sources to power automobiles. This would help reduce the use of fossil fuels in automobiles and hence reduce the resulting environmental pollution. Also since the turbine adds to the weight of the vehicle the aim also is to minimize the weight of the turbine. Extensive structural analysis is done for this purpose to choose a material which would be both light weight and also be able to withstand the stresses developed. In the current paper the drag force produced in automobiles is harvested by using a convergent divergent nozzle mounted below the chassis of the car. Initially drag analysis is done in order to determine the increase in drag force produced after mounting of the nozzle. It is found from existing literature that the drag increases by 3.4% after the mounting of the nozzle making it possible the mounting of a nozzle beneath the car. Additionally exhaust gases is also allowed to pass through the same duct to increase the mass flow to the turbine and thus generate more energy. This is made to strike the blades of a 2 stage axial flow turbine whose rotation generates energy. The power output from the turbine is the parameter of interest. This energy can also be stored in batteries and be used to run auxiliary equipment of the automobile including the air conditioner. The exhaust gases will be passed through a catalytic converter before striking the blades of the turbine in order to prevent corrosion of the blades. Computational Fluid Dynamics (CFD) is used to validate the concept and also come up with a design that maximizes energy generation by such turbines. Numerical results obtained by simulation are validated by theoretical calculation based on turbines inlet and outlet velocity triangles. The future scope of the project would include the use of multiple nozzles in order to study its performance.

Commentary by Dr. Valentin Fuster
2016;():V001T14A004. doi:10.1115/ES2016-59594.

As wind energy is established as a sustainable alternative source of electricity, very large-scale wind farms with hundreds of turbines are becoming increasingly common. For the optimal design of wind farm layouts, the number of decision variables is at least twice the number of turbines (e.g., the Cartesian coordinates of each turbine). As the number of turbines increases, the computational cost incurred by the optimization solver to converge to a satisfactory solution increases as well. This issue represents a serious limitation in the computer-aided design of large wind farms. Moreover, the wind farm domains are typically highly constrained including land-availability and proximity constraints. These non-linear constraints increase the complexity of the optimization problem and decrease the likelihood of obtaining even a feasible solution. Several approaches have been proposed for micrositing of wind turbines, including random searches, mixed-integer programs, and metaheuristics. Each of these methods has its own trade-off between the quality of optimized layouts and the computational cost of obtaining the solution. In this paper, we demonstrate the capability of non-linear mathematical programming for optimizing very large-scale wind farms by leveraging explicit, analytical derivatives for the objective and constraint functions, thus overcoming the aforementioned limitations while also providing convergence and local optimality guarantees. For that purpose, two large farms with hundreds of turbines and significant land-use constraints are solved on a standard personal computer.

Commentary by Dr. Valentin Fuster
2016;():V001T14A005. doi:10.1115/ES2016-59639.

The performance of Savonius wind turbine can be improved by increasing the effective wind velocity. One of the methods of improving the effective wind velocity is using directional augmentation technique, which actually affects the Omnidirectional capability of the Savonius rotor. This paper works on this method by using convergent nozzle at the outlet of the rotor. The whole work is based on Metamodeling based optimization and numerical simulation. Reynolds averaged Navier-stokes equation (RANS) based turbulence model has been used for simulations, such as static simulation and dynamic simulation. The CFD simulations are validated against previously published experimental data. The optimization procedure is performed by integrating the Design of Experiment (DOE), Computational Fluid Dynamics (CFD), Response Surface Model (RSM) and analysis of variance (ANOVA). The meta-model is able to identify significant design variable and the interactions. The proposed optimal nozzle is shown to improve the coefficient of the moment from 0.3 to 0.44.

Commentary by Dr. Valentin Fuster

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