ASME Conference Presenter Attendance Policy and Archival Proceedings

2018;():V001T00A001. doi:10.1115/ES2018-NS.

This online compilation of papers from the ASME 2018 12th International Conference on Energy Sustainability (ES2018) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

Nexus: Energy, Water, Climate, Food

2018;():V001T01A001. doi:10.1115/ES2018-7112.

Access to energy is crucial in tackling many of the current global development challenges that impact on people’s economic, health and social well-being as well as the ability to meet the commitments of reducing carbon emissions through clean energy use. Despite increased attention from multiple governments and agencies, energy poverty remains a serious sustainable development issue in many developing countries. To date, most research have focused on general access to electricity and the generation of clean energy to replace fossil fuels, failing to address the lack of basic access to clean energy for cooking and heating. More people in the world lack access to clean cooking fuels than to electricity. This issue is one aspect of a broader research which investigates the impacts of optimized energy policy and energy business models on sustainable development in developing countries.

Commentary by Dr. Valentin Fuster
2018;():V001T01A002. doi:10.1115/ES2018-7304.

In a PEMFC (Proton electrolyte membrane fuel cell), water transport mechanism inside the membrane is very important in performance and durability of whole fuel cell stack. Diffusion of water through the membrane is governed by humidity conditions of outer layers and the humidity conditions of gases depend on temperature, pressure and operating pressures. Since those parameters are varied non-linearly, it is necessary to investigate water transport mechanism by concentration difference between both sides of membrane.

In this study, water contents of Nafion® membrane is measured in terms of relative humidity, temperatures, and operating pressure. Water diffusion is also measured at different pressures in both sides. Test chamber is designed to fix membrane in the middle of chamber and the membrane separates chambers in two spaces. Parametric study is conducted to measure the water contents of membranes in terms of temperatures 30°C, 50°C, 70°C, 90°C and 0 to 100% relative humidity. When the water diffusivity is calculated by measured data, the water concentrations in both sides are determined by harmonic averages of inlet and exit water humidity. Additionally, water flux is also investigated in terms of both sides humidity, operating pressure and temperatures. As a result, the water diffusion coefficient was explained by the operating temperature and the relative humidity and operating pressures.

Topics: Membranes , Water
Commentary by Dr. Valentin Fuster
2018;():V001T01A003. doi:10.1115/ES2018-7349.

Wastewater treatment plants (WWTPs) are a significant energy consumer, yet there are several opportunities of implementing on-site power generation systems. Within the treatment process, the high flow rate of effluent is produced and discharged to a nearby water body by gravity. Thus, hydro turbines can be utilized to generate power in such application due to a difference in elevation and high flow rate. This paper presents a case study of introducing a hydro turbine in wastewater treatment plant in Wisconsin and evaluating the power output in addition to determining the energy savings. The wastewater treatment plant considered in this study has an effluent flow rate of 190 MGD (million gallons per day) and elevation difference of 3 meters (10 feet) between the final stage of treatment and the discharge point. Based on the aforementioned parameters; hubless rim-drive Kaplan type hydro turbine (RDT) is the optimal choice to be used in such application. The RDT is designed and optimized by using in-house code. A computational fluid dynamics (CFD) software is applied to evaluate the performance of the proposed model, and the system is simulated through HOMER software to validate the results generated by the CFD. The expected savings is estimated to be 1,564 MWh/year.

Commentary by Dr. Valentin Fuster
2018;():V001T01A004. doi:10.1115/ES2018-7564.

A precise calculation of the environmental burden of food products is a prerequisite for creating food eco-labeling as a strategy for environmental impact mitigation. Life cycle assessment (LCA) is widely used for this purpose, and proxy data is traditionally used due to the shortage of data. Uncertainties are introduced in this process since food products contain a variety of origins. In this study, data from the United States Department of Agriculture (USDA) is used to examine the temporal and geographic variability of the global warming potential (GWP) of seven kinds of field crops. Artificial neural network (ANN) models are then used to predict the GWP of these products at both product and category levels based on temporal and spatial variables such as soil properties, climate, latitude and elevation. The results show that temporally, a monotonic GWP trend was found in corn, soybean and winter wheat. The average geographic variability is more than 27% and is larger than temporal variability. ANN was proven to be a good prediction tool at the product level, with a coefficient of correlation (CC) of at least 0.78 in the simplest model and higher CCs when the number of neurons increases. Predictions with ANN at the category level shows that the selected variables cannot fully encompass all temporal and geographical variability.

Commentary by Dr. Valentin Fuster

Smart and Cyber-Physical Systems

2018;():V001T02A001. doi:10.1115/ES2018-7184.

This paper presents the feasibility and economics of using fuel cell backup power systems in telecommunication cell towers to provide grid services (e.g., ancillary services, demand response). The fuel cells are able to provide power for the cell tower during emergency conditions. This study evaluates the strategic integration of clean, efficient, and reliable fuel cell systems with the grid for improved economic benefits. The backup systems have potential as enhanced capability through information exchanges with the power grid to add value as grid services that depend on location and time. The economic analysis has been focused on the potential revenue for distributed telecommunications fuel cell backup units to provide value-added power supply. This paper shows case studies on current fuel cell backup power locations and regional grid service programs. The grid service benefits and system configurations for different operation modes provide opportunities for expanding backup fuel cell applications responsive to grid needs.

The objective of this work primarily focuses on how fuel cells can become a significant part of the telecom backup power to reduce system costs, environmental impact, and dependence on fossil fuels, while ensuring continuity of indispensable service for mobile users. The study identifies the approaches on the fuel cell application through nano/microgrids for an extensive network of fuel cells as distributed energy resources. The possibilities of various application scenarios extend the fuel cell technologies and microgrid for reliable power supply.

Commentary by Dr. Valentin Fuster
2018;():V001T02A002. doi:10.1115/ES2018-7295.

This paper presents a co-simulation platform which combines a building simulation tool with a Cyber-Physical Systems (CPS) approach. Residential buildings have a great potential of energy reduction by controlling home equipment based on usage information. A CPS can eliminate unnecessary energy usage on a small, local scale by autonomously optimizing equipment activity, based on sensor measurements from the home. It can also allow peak shaving from the grid if a collection of homes are connected. However, lack of verification tools limits effective development of CPS products. The present work integrates EnergyPlus, which is a widely adopted building simulation tool, into an open-source development environment for CPS released by the National Institute of Standards and Technology (NIST). The NIST environment utilizes the IEEE High Level Architecture (HLA) standard for data exchange and logical timing control to integrate a suite of simulators into a common platform. A simple CPS model, which controls local HVAC temperature set-point based on environmental conditions, was tested with the developed co-simulation platform. The proposed platform can be expanded to integrate various simulation tools and various home simulations, thereby allowing for co-simulation of more intricate building energy systems.

Commentary by Dr. Valentin Fuster
2018;():V001T02A003. doi:10.1115/ES2018-7461.

Residential energy applications have become an important domain of cyber-physical systems. These applications provide significant opportunities for end-users to reduce their electricity costs and for the utilities to balance their supply and demand in the most effective way. One of the most important applications is predicting the total energy usage of a house. However, an accurate time-series prediction may require significant amount of data, e.g. per appliance energy consumption values, that need costly installations, data storage units, and computation and communication devices. In this paper, we propose a framework that uses a forward-selection-based input filtering mechanism for residential prediction applications. Our framework can effectively reduce the amount of data required for residential energy prediction without sacrificing prediction performance. We demonstrate that 94% of the houses can leverage our method, which leads to up to 80% reduction in required data, greatly reducing the system cost and overhead.

Commentary by Dr. Valentin Fuster
2018;():V001T02A004. doi:10.1115/ES2018-7496.

Ambient energy harvesting using piezoelectric transducers is becoming popular to provide power for small microelectronics devices. The deflection of tires during rotation is an example of the source of energy for electric power generation. This generated power can be used to feed tire self-powering sensors for bicycles, cars, trucks, and airplanes. The aim of this study is to optimize the energy efficiency of a rainbow shape piezoelectric transducer mounted on the inner layer of a pneumatic tire for providing enough power for microelectronics devices required to monitor tires. For this aim a rainbow shape piezoelectric transducer is adjusted with the tire dimensions and excited based on the car speed and strain. The geometry and load resistance effects of the piezoelectric transducer is optimized using Multiphysics modeling and finite element analysis.

Commentary by Dr. Valentin Fuster

Geothermal Technologies

2018;():V001T03A001. doi:10.1115/ES2018-7330.

The short-cycling operation of a heat pump decreases energy consumption efficiency. Short-cycling operations of GSHP (Ground Source Heat Pump System) occur when the ON / OFF control of a heat pump is used a partial load condition. It is considered effective that GSHP with capacity controls installs to suppress short-cycling operations. However, there is no report on any continuous operations by capacity control GSHP in actual operations.

We confirmed that GSHP (water to water) with capacity control operates short-cycling in the residence. Short-cycling operations were occurred a sudden load fluctuation due to opening or closing of the valves.

We conducted effective verification experiments of the thermal storage device at the artificial heat load fluctuations condition. When the thermal storage device installed upstream brine circulation line of the heat pump with the capacity control, continuous operations are performed. It was under the condition at the heating heat load of 5 kW is turned ON / OFF every 20 minutes. In this case, energy consumption efficiency of a heat pump is 13% higher than the efficiency without the thermal storage device.

Commentary by Dr. Valentin Fuster
2018;():V001T03A002. doi:10.1115/ES2018-7418.

In geothermal heating and cooling, there exists an opportunity to improve the efficiency by utilizing non-uniform soil properties of a ground source heat exchanger during installation. This paper presents a gradient approach based upon finite element mathematics to determine an optimal distribution of heterogeneous soils with varying thermal conductivities. The numerically simulated case studies demonstrate the good performance of this algorithm to minimize the cross-talk of heat flux between pipes and maximize the overall efficiency.

Commentary by Dr. Valentin Fuster

Conversion and Processing of Biofuel and Alternative Fuel

2018;():V001T04A001. doi:10.1115/ES2018-7197.

In a move to reduce dependence on imported fossil fuels, develop and utilize indigenous renewable and sustainably-sourced clean energy sources, the Philippines enacted the Biofuels Act of 2006 (or Republic Act 9367) that mandated blending of biodiesel with commercially sold diesel fuels which presently is at 2% coconut methyl ester (CME) by volume. Deliberations are underway to shift to 5% by volume so that data on the effects on performance and emissions of percentage blends are necessary. This study presents fuel consumption and emissions measurements of an in-use passenger van with a common-rail direct injection (CRDI) powertrain fueled with 2, 5, 10, & 20 percent CME-diesel blends by volume (designated as B2, B5, B10, & B20 respectively) driven on the Japanese 10–15 Mode drive cycle. Results indicate B2-B20 had only a marginal effect on heating values, fuel blend density, and maximum power. Relative to neat diesel, the blends showed a 1–5% lower specific fuel consumption (SFC) with B5 lowest. Mileage was 1–5% higher with the blends with B5 highest. CO decreased with increasing blend. THC emissions of B1-B20 were roughly half that of diesel. NOx from the CME blends was marginally lower than diesel. The CO and THC trends agreed with published literature and usually ascribed to overall lean mixtures and increased amount of oxygenated fuel at higher CME blends. The NOx results need further investigation as it seemed to contradict other studies. Based on these results, B5 yielded the best combination of fuel economy and emissions improvement over neat diesel and B2 without performance loss.

Topics: Diesel , Emissions
Commentary by Dr. Valentin Fuster
2018;():V001T04A002. doi:10.1115/ES2018-7273.

Portland General Electric’s (PGE) Boardman plant is a nominal 600 megawatt (MW) coal fired unit that burns sub-bituminous Powder River Basin (PRB) coal from Wyoming. This paper will cover the experience and results of PGE’s Boardman plant operating on 100% torrefied wood (TW) pellets at 255 MW consuming almost 5000 tons of pellets. Results were positive and include suitable handing after inclement weathering for months. Pulverizers were able to handle the TW pellets with adjustments, resulting in near 100% combustion efficiency. Particulates were controlled with an electrostatic precipitator (ESP). Topics investigated include torrefied wood production, fuel handling and storage on the front end of the test. Fuel handling, pulverization, combustion, emissions, and ESP performance were monitored during the test and are reported here. Several one mill tests were conducted prior to the 100% test to evaluate and improve mill performance. This test showed that a pulverized coal (PC) boiler can operate on 100% TW fuel with minimal operational changes.

Topics: Wood products , Boilers , Coal
Commentary by Dr. Valentin Fuster
2018;():V001T04A003. doi:10.1115/ES2018-7351.

This paper investigates the thermoelectric characteristics of cross-flow planar type solid oxide fuel cell (SOFC) with natural gas as fuel by using a three-dimensional numerical model. The results reveal that temperature and reactant concentration increase gradually along the direction of fuel gas flow, and the reactant concentration increases in the first and subsequently decreases. In addition, the lower the temperature, the higher ideal electromotive force is as well as the less actual output electromotive force. The hydrogen concentration is positively correlated with the current density and the ideal electromotive force. However, increasing the mass flow continuously beyond the reasonable range can decrease the current and electrochemical reaction intensity. Variation in wall thickness was also simulated and found that increasing the thickness would result in higher intensity of electrochemical reaction and increased current density but at the cost of low efficiency in SOFC. Thus an optimal design can make a balance between fuel utilization and output power of SOFC.

Commentary by Dr. Valentin Fuster
2018;():V001T04A004. doi:10.1115/ES2018-7369.

Biomass offers the potential to economically produce hydrogen via gasification from an abundant and renewable feedstock. When hydrogen is produced from a biomass gasifier, it is necessary to purify it from syngas streams containing components such as CO, CO2, N2, CH4, and other products. Therefore, a challenge related to hydrogen purification is the development of hydrogen-selective membranes that can operate at elevated temperatures and pressures, provide high fluxes, long operational lifetime, and resistance to poisoning while still maintaining reasonable cost. Palladium based membranes have been shown to be well suited for these types of high-temperature applications and have been widely utilized for hydrogen separation. Palladium’s unique ability to absorb a large quantity of hydrogen can also be applied in various clean energy technologies, like hydrogen fuel cells. In this paper, a fully analytical interatomic Embedded Atom Potential (EAM) for the Pd-H system has been developed, that is easily extendable to ternary Palladium based hydride systems such as Pd-Cu-H and Pd-Ag-H. The new potential has fewer fitting parameters than previously developed EAM Pd-H potentials and is able to accurately predict the cohesive energy, lattice constant, bulk modulus, elastic constants, melting temperature, and the stable Pd-H structures in molecular dynamics (MD) simulations with various hydrogen concentrations. The EAM potential also well predicts the miscibility gap, the segregation of the palladium hydride system into dilute (α) and concentrated (β) phases.

Commentary by Dr. Valentin Fuster
2018;():V001T04A005. doi:10.1115/ES2018-7531.

Biomass torrefaction is a thermal pretreatment which takes place at a temperature between 200–300 °C in a non-oxidative environment. The process requires thermal energy for drying and torrefying the raw biomass. The amount of the required heat may vary depending on the biomass moisture content, operating temperature and residence time. The volatiles released during the torrefaction are usually burnt in a combustor to meet the heat requirement of the process. If the energy content of the volatiles is less than the thermal energy required for the process, the operation of the torrefaction unit is below the autothermal mode so an auxiliary fuel such as natural gas is burnt together with the volatiles.

This paper investigates autothermal operation of a torrefaction unit which consists of a dryer, a torrefaction reactor, a combustor, and two heat exchangers. An experimentally validated process model is employed to identify a relation between the moisture content, torrefaction temperature, and residence time at autothermal operation. The model is capable of predicting the composition of volatiles and torrefied biomass, mass and energy yields, process heat requirement, and CO2 emissions. The results are graphically presented allowing one to determine whether a torrefaction unit operates below or above the autothermal mode at given torrefaction temperature, residence time and moisture content. Furthermore, the effect of the main operating parameters on the carbon dioxide emissions of the torrefaction unit is discussed.

Topics: Biomass
Commentary by Dr. Valentin Fuster
2018;():V001T04A006. doi:10.1115/ES2018-7553.

A work on biogas potentials evaluation of household wastes in Johannesburg metropolitan area using the Automatic Methane Potential Test System (AMPTS) II is presented. The AMPTS II consists of three units — the sample incubation unit, CO2 absorption unit and the gas volume measuring device. Organic fraction of wastes collected from households within Johannesburg metropolis were sorted, ground and prepared into slurry by mixing with water. Microcrystalline cellulose powder with 3.5% loss on drying and 0.28g/cc density was used as control substrate while anaerobic sludge collected from a functional biogas reactor was used as inoculum. Anaerobic sludge was classified as sample A, household waste containing mainly non-food waste was labelled sample B, sample C was microcrystalline cellulose used as positive control while household waste composing of mainly food waste was classified as sample D. Each sample was fed into a 50 mL bottle reactor in triplicates and stirred in a clockwise direction continuously for 5 minutes with a pulse interval of 1 minute at a set temperature of 37°C for 30 days retention time. NaOH solution was prepared into solution following standard procedure and mixed with a prepared 0.4 % Thymolpthalein solution. The resultant solution was poured into the 100 mL bottles of the CO2 unit. Produced biogas was measured through water displacement in the volumetric bath and values read off through a data-logger connected to a laptop. Results indicated biochemical methane potential (BMP) of 69–800 NmL/gvs and biogas composition with more than 50% methane before CO2 fixing and over 80% after CO2 fixing. Given that the average amount of waste generated per person per day in South Africa is over 0.7 kg, there is huge potentials for biogas production from household wastes in Johannesburg.

Topics: Biogas , Cities , Methane
Commentary by Dr. Valentin Fuster
2018;():V001T04A007. doi:10.1115/ES2018-7571.

To reduce the dependency on fossil-based energy resources, the utilization of renewable fuels in unmodified diesel engines is gaining more emphasis from researchers in the recent years. The aim of the current study is to take part in the efforts being made to this regard by experimentally investigating a compression ignition engine fueled with different fuels ((diesel, diesel-biodiesel (B20), and diesel-biodiesel-butanol (BU20)) for their performance and emissions comparison. The experimental study was conducted in a water cooled single-cylinder direct injection (DI) diesel engine. It was operated at a constant engine operation speed of 1800 rpm and under varied engine load conditions. It is found that BU20 shows promising results in terms of performance and emissions characteristics as compared to using B20 and D100. Butanol addition to diesel-biodiesel blends is considered as an appropriate solution of higher density and viscosity the blend and thus for the sustainable usability of biodiesel. Maximum thermal efficiency improvement of 3.18% was observed at an engine load of 75%. The NOx emission was improved with BU20 as compared to the conventional diesel fuel (D100) at most of the engine loads. As an improvement on the engine performance and emissions is reported from the current study, the BU20 fuel blends can be used in similar engines with no further engine retrofitting. This blend can be a good environmental friendly fuel that can serve in the reduction of fossil-based diesel fuels. A further study on diesel engine tribology is required.

Commentary by Dr. Valentin Fuster

Distributed Energy Systems

2018;():V001T05A001. doi:10.1115/ES2018-7158.

This paper presents a methodology to predict and optimize performance of an organic Rankine cycle (ORC) using a back propagation neural network (BPNN) for diesel engine waste heat recovery. A test bench of an ORC with a diesel engine is established to collect experimental data. The collected data is used to train and test a BPNN model for performance prediction and optimization. After evaluating different hidden layers, a BPNN model of the ORC system is determined with consideration of mean squared error and correlation coefficient. The effects of key operating parameters on the power output of the ORC system and exhaust temperature at the outlet of the evaporator are evaluated using the proposed model and further discussed. Finally, a multi-objective optimization of the ORC system are conducted for maximizing power output and minimizing exhaust temperature at the outlet of the evaporator based on the proposed BPNN model. The results show that the proposed BPNN model has a high prediction accuracy and the maximum relative error of the power output is less than 5%. It also shows that when the operations are optimized based on the proposed model, the power output of the ORC system can be higher than the experimental results.

Commentary by Dr. Valentin Fuster
2018;():V001T05A002. doi:10.1115/ES2018-7181.

Compressed air energy storage is an effective energy storage technology to solve the instability of wind power in distributed energy resources. In this paper, a multistage compressed air energy storage system optimization model is constructed based on the energy conservation equation. Then the system is optimized by differential evolution to improve the system efficiency. Optimal pressure ratios are proposed to distribute the pressures of compressors and expanders. The impact of pressure ratio distribution curve on the system energy efficiency suggests that the change curve of the characteristics vary in different heat exchanger performance. Results show that the change of thermal transfer reactor performance leads to the variety of optimal distribution pressure ratio and energy efficiency of the system. In addition, the differential ratio distribution factor can be effective on the pressure ratio of reasonable allocation. System efficiency optimization results increased by about 1% compared mean value.

Commentary by Dr. Valentin Fuster
2018;():V001T05A003. doi:10.1115/ES2018-7223.

Photovoltaic thermal collectors (PVT) combines technologies of photovoltaic panels and solar thermal collectors into a hybrid system by attaching an absorber to the back surface of a PV panel. PVT collectors have gained a lot of attention recently due to the high energy output per unit area compared to a standalone system of PV panels and solar thermal collectors. In this study, performance of a liquid cooled flat PVT collector under the climatic conditions of Abu Dhabi, United Arab Emirates was experimentally investigated. The electrical performances of the PVT collector was compared to that of a standalone PV panel. Moreover, effect of sand accumulation on performance of PVT collectors was examined. Additionally, effect of mass flow rate on thermal and electrical output of PVT collector was studied. Electrical power output is slightly affected by changes in mass flow rate. However, thermal energy increased by 22% with increasing flow rate. Electrical power output of a PV panel was found to be 38% lower compared to electrical output of PVT collectors. Dust accumulation on PVT surface reduced electrical power output up to 7% compared with a reference PVT collector.

Commentary by Dr. Valentin Fuster
2018;():V001T05A004. doi:10.1115/ES2018-7238.

Electric vehicles (EVs) are receiving more attention these days because they are environmentally friendly (no emissions) and are much quieter than internal combustion engine vehicles with rapidly decreasing prices. One of the serious limitations of EVs is the limited driving range. When conventional heating and air conditioning systems are used in winter and summer, the driving range is reduced further because they consume a lot of electric energy stored in the batteries. A thermoelectric cooling system integrated with thermal energy storage has been identified as an attractive alternative to traditional air conditioning in electric vehicles. The main goal of such a system is to minimize the amount of electricity that is drawn for air-conditioning from the electric battery of the vehicle, thus eliminating further reduction in driving range. Not only is the alternative more light weight than the conventional vapor compression based air-conditioning system, it also reduces the amount of electricity drawn from the battery. The proposed system is comprised of thermal energy storage (TES) employing phase change materials (PCMs), thermoelectric electric modules, and a fan. The TES, also referred to as a thermal battery here, can be charged before at home or at a charging station before driving like the electric battery, and is discharged when used in driving. This study involved the design and development of a TES for EVs employing computational fluid dynamics and heat transfer analyses. The model includes all the key components such as thermoelectric (Peltier) modules, heat sinks and the PCM. Various simulations for thermal battery charging and discharging have been conducted to demonstrate the feasibility of incorporating TES coupled with thermoelectric modules.

Commentary by Dr. Valentin Fuster
2018;():V001T05A005. doi:10.1115/ES2018-7532.

Traditional heat transfer techniques have become inadequate for many applications today and innovation of new technologies has become an urgent necessity. From another angle, securing electrical power remote areas in unconventional ways is receiving widespread attention. In this study, we present a new technique to dissipate heat, which is suitable in narrow and slanted places, as well as, generate electricity. The system consists of a permanent magnet (PM) and a spring where they act as opposing forces on a ferromagnetic disk moving in a specific space. Above the Curie temperature (Tc) of the ferromagnet, spring force (Fspring) overcomes the strength of the PM due to loss the magnetic susceptibility of the ferromagnet. PM’s force is gradually increasing and overcomes the Fspring due to the cooling of the ferromagnetic. Thermally, the system consists of high and low temperature zones and the ferromagnetic works as an active heat carrier. The opposing forces of the PM and the spring make the ferromagnetic moves in two opposite directions. COMSOL Multiphysics 5.2a software is used to get the simulation results in this study. This technique is suitable for many applications especially when heat transfer is required in the horizontal or oblique direction. This technique provides clean energy using only a waste heat from anywhere as a source.

Commentary by Dr. Valentin Fuster

Sustainability and Society

2018;():V001T06A001. doi:10.1115/ES2018-7292.

The cyclic effect of energy poverty and economic poverty has been conclusively evidenced primarily from the experiences of developing World. In the developing countries, struggle to meet the basic energy needs impacts the life of the poorer section in terms of cost of health, education and quality. However, considering the adequate biomass resources and sustainable technologies for conversion of surplus biomass into useful form of energy; integration of the surplus resources with appropriate technology offers opportunities to address both energy and economic poverty. In this study, feasibility of some proven options of bioenergy based energy technologies and enterprises are investigated to understand their prospects to address energy and economic hardship considering a case study from India and analyzed its replicability in South Africa. Resources inventories, avenues of additional income generation and long term impact of selected bioenergy enterprise options (biogas and producer gas and improved stove) are investigated in the context of both the countries. Organic fertilizer (vermicompost), mushroom and community based agro-industries are some of the prospective entrepreneurial activities which can be supported by the bioenergy options. Considering the abundance and characteristics, feasibility of converting surplus biomass resources (crop residue, manure, food waste) into required energy along with revenue earning avenues is indicated by the study. However, there are social and managerial issues which required to be addressed besides provisions for financial incentives to realize the benefits of such integrated systems.

Topics: Biomass
Commentary by Dr. Valentin Fuster
2018;():V001T06A002. doi:10.1115/ES2018-7327.

Residential energy consumption constitutes a significant portion of the overall energy consumption. There are significant amount of studies that target to reduce this consumption, and these studies mainly create mathematical models to represent and regenerate the energy consumption of individual houses. Most of these models assume that the residential energy consumption can be classified and then predicted based on the household size. As a result, most of the previous studies suggest that household size can be treated as an independent variable which can be used to predict energy consumption. In this work, we test this hypothesis on a large residential energy consumption dataset that also includes demographic information. Our results show that other variables like income, geographic location, house type, and personal preferences strongly impact energy consumption and decrease the importance of household size because the household size can explain only 26.55% of the electricity consumption variation across the houses.

Commentary by Dr. Valentin Fuster
2018;():V001T06A003. doi:10.1115/ES2018-7352.

Through analyzing the impact of the factors of catalyst deactivation, different factors are classified according to timeliness characteristics. In this research, experiments were made under the condition of coal combustion flue gas on a coal-fired boiler to study the characteristics of the early deactivation of the SCR catalyst. Analysis shows that the main cause of early deactivation of catalyst is chemical poisoning (mainly alkali metal) and pores clogging on the surface of the catalyst. While the main cause of long-term deactivation is deeper chemical poisoning, pores clogging and the chemical form changes of elements on the surface of the catalyst. Through analyzing the influence of the factors of catalyst deactivation, separate factors are classified according to timeliness characteristics. This research provides a strong fundamental support to clear the deactivation mechanism of the SCR catalyst.

Topics: Coal , Catalysts , Flue gases
Commentary by Dr. Valentin Fuster
2018;():V001T06A004. doi:10.1115/ES2018-7413.

Accurate control of thermal conditions in large space buildings like an underground metro station is a significant issue because passengers’ thermal comfort must be maintained at a satisfactory level. The large eddy simulation (LES) model was adopted while using the computational fluid dynamics (CFD) software “STAR CCM+” to set up a CFD station model to predict static air temperature, velocity, relative humidity and predicted mean vote (PMV), which indicates the passengers’ thermal comfort. The increase in the number of passengers using the model station is taken into consideration. The studied cases covered all the possible modes of the station box, these modes are (1) the station box is empty of trains, (2) the presence of one train inside the station box, (3) the presence of two trains inside the station box. The objective is to bring the passengers’ thermal comfort in all modes to the acceptable level. The operation of under platform exhaust (UPE) system is considered in case of train presence inside the station box. The use of UPE is more energy efficient than depending entirely on the air conditioning system to maintain the thermal conditions comfortable.

Commentary by Dr. Valentin Fuster
2018;():V001T06A005. doi:10.1115/ES2018-7465.

There is an increasing need for the integration of renewable energy into the energy sector in Egypt. As the electricity subsidies are residing for consumers in Egypt, electricity prices are increasing. This increase in energy prices can be mitigated by the integration of renewable energy technologies. One of the most promising renewable energy technologies that will help stabilize the energy situation in Egypt, is Solar Thermal Energy. Solar Thermal Energy has a great potential in Egypt due to the availability and intensity of direct irradiance in Egypt. Therefore, Egypt has an amazing opportunity as a developing country to start perusing solar thermal technologies; these technologies include decentralized and centralized technologies. Decentralized technologies are targeted more for regular consumers and centralized technologies are targeted more for power generation and industries.

Commentary by Dr. Valentin Fuster
2018;():V001T06A006. doi:10.1115/ES2018-7550.

The Industrial Assessment Center at University of Wisconsin-Milwaukee (WM-IAC) has implemented over 100 industrial energy, waste, and productivity assessments, and has recommended $9.5 million of energy and operational savings with about 950 recommendations since it was re-established in 2011. This paper analyzes the assessments, and the recommendations were performed over two years only, 2014 and 2015. During these two years, a total of 40 assessments were created by visiting different manufacturing facilities with the analysis of the data gathered and processed. The determinants of the data were the number of recommendations, recommended energy savings (in kWh/year), recommended energy cost savings (in US$/year), implemented energy savings (in US$/year), the Standard Industrial Code (SIC) and the groups of Energy Efficiency Opportunities (EEOs). Such an analytical study was meant to reveal the significance of EEO groups through a variety of SICs in terms of the potential for energy savings, particularly focused towards choosing plant facilities for IAC assessments. Additionally, this paper could be considered as a guide for plant managers, energy engineers and other personnel involved in the energy assessment process. Conclusions are inferred with respect to the most promising EEOs that can be resolved based on the characteristics of the manufacturing plants visited. The information investigated can pave the way for composing energy demanding industries and expose priority goal areas regarding minimizing the energy consumption.

Commentary by Dr. Valentin Fuster

Electrochemical Energy Conversion and Storage

2018;():V001T07A001. doi:10.1115/ES2018-7120.

The vanadium/air redox flow battery working performance will be affected by many factors, including the quality of the membrane used and the working conditions. The crossover rate of vanadium ions for the membrane can determine the capacity due to the ion diffusion and the side reactions. The high reaction temperature for the VARFB also influence the diffusion coefficient. Based on Fick’s Law, by using Arrhenius Equation to predict the temperature effect, and take into consider that the mass balance for each reacting ions and reaction temperature, the dynamic modelling on capacity decay can be developed. Then by using Nernst Equation, the voltage change of VARFB can also be calculated. This dynamic model will predict the concentration change of the battery as a function of time, after benchmarking with the experimental data, this model can compare the performance of the battery with a different order of diffusion coefficient membranes in different working condition. This model can also predict the contacting V2+ concentration to the electrode and catalyst to monitor the working efficiency.

Commentary by Dr. Valentin Fuster
2018;():V001T07A002. doi:10.1115/ES2018-7203.

Airports, one of the important transportation components in this modern age, are under continuous improvement especially in regard to energy sustainability. While most work is concentrated on large airports, smaller airports which are mostly scattered around rural areas seem to be better opportunities for renewable energy utilization. However, while renewable energy has come into use at airports over the past decade, it has been at a slow pace and has not included storage. A reliable storage system can significantly increase the power reliability of a small airport and make a renewable energy system viable.

Acquiring the technical requirements of a facility based on its characteristics enables the designer to evaluate the power source options and develop an efficient storage system. The current paper analytically develops a framework to design and integrate an energy storage method for a renewable system into a small airport facility. The framework details include methods for energy storage which are environmentally acceptable in combination with renewable energy sources to produce electrical power for the on-site facilities. The technical analysis which leads to the sizing of the storage unit initiates with categorizing different methods for energy storage and their applicability to an airport facility for off-grid and on-grid modes.

Based on the results and conclusions from the first step, the search is narrowed down to mediums for electricity storage for a wind farm or solar power plant. In such a case, the main applications of the storage unit could be either to supply power to the facility during the transition time from the renewable source to the main grid or to regulate the power frequency of the generation unit. Capacitors and batteries were selected as the two options for the given power requirement of the facility. Considering the wide variety of available technologies and lower costs, the appropriate storage system is proposed for both long term and short term applications. A table is presented to compare available battery technologies and their respective storage capacities.

Topics: Energy storage
Commentary by Dr. Valentin Fuster
2018;():V001T07A003. doi:10.1115/ES2018-7224.

This paper presents an application of MRI to measure flow distribution in fuel cell channels. Solid Oxide Fuel Cells (SOFC) are able to efficiently produce electricity directly from the oxidation of the natural gas by electrochemical conversion. The distribution of fuel gas between the high numbers of parallel flow paths within the fuel cell assembly is critically important to ensure high efficiency and uniform conditions within the fuel cell assembly. Practical approaches in conjunction with numerical models are needed to understand and control the physical processes taking place within fuel cells in order to design them to be efficient and reliable. The paper outlines a non-invasive experiment using magnetic resonance imaging (MRI) to measure the distribution of flow within an SOFC subassembly.

The method quantifies the flow distribution by modelling the gas using water at Reynolds similar conditions. Water has a magnetic moment that can be imaged using an MRI scanner. Two-dimensional cross-section scans were taken perpendicular to the direction of flow in the fuel cell channel to measure area and velocity. The study evaluated a range of image resolutions and outlined how the data was processed to provide mass flow rates in each channel using the known fluid properties.

At the highest image resolution the total mass flow rate was within 1% of the independent measurement from the experimental rig. The distribution of flow between the channels showed a similar trend to the computational model. The initial results demonstrate the feasibility for the method to measure flow in the SOFC channels.

Commentary by Dr. Valentin Fuster
2018;():V001T07A004. doi:10.1115/ES2018-7262.

Synthesis of hyper branched polymer (HBP) based electrolyte has been examined in this study. A real world lithium-air battery cell was fabricated using the developed HBP electrolyte, oxygen permeable air cathode and lithium metal as anode material. Detailed synthesis procedures of hyper branched polymer electrolyte and the effect of different operation conditions on the real-world lithium-air battery cell were discussed in this paper. The fabricated battery cells were tested under dry air with 0.1mA∼0.2mA discharge current to determine the effect of different operation conditions such as carbon source, electrolyte types and cathode processes. It was found that different processes affect the battery cell performance significantly. We developed optimized battery cell materials upon taking into account the effect of different processes. Several battery cells were fabricated using the same optimized anode, cathode and electrolyte materials in order to determine the battery cells performance and reproducibility. Experimental results showed that the optimized battery cells were able to discharge over 55 hours at over 2.5V. It implies that the optimized battery cell can hold charge for more than two days at over 2.5V. It was also shown that the lithium-air battery cell can be reproduced without loss of performance with the optimized battery cell materials.

Commentary by Dr. Valentin Fuster
2018;():V001T07A005. doi:10.1115/ES2018-7340.

The chlor-alkali industry produces significant amounts of hydrogen as byproduct and an interesting benefit can be obtained by feeding hydrogen to a PEM fuel cell unit, whose electricity and heat production can cover part of the chemical plant consumptions. The estimated potential of such application is up to 1100 MWel installed in the sole China, a country featuring a large presence of chlor-alkali plants.

This work presents the modeling, development and first experimental results from field tests of a 2 MW PEM fuel cell power plant, built within the European project DEMCOPEM-2MW and installed in Yingkou, China as the current world’s largest PEM fuel cell installation. After a preliminary introduction to the market potential of PEM Fuel cells in the chlor-alkali industry, it is first discussed an overview of project’s MEA and fuel cell development for long life stationary applications, focusing on the design-for-manufacture process and the high-volume manufacturing route developed for the 2MW plant.

The work then discusses the modeling of the power plant, including a specific lumped model predicting FC stack behavior as a function of inlet streams conditions and power set point, according to regressed polarization curves. Cells performance decay vs. lifetime reflects long-term stack test data, aiming to evidence the impact on overall energy balances and efficiency of the progression of lifetime. BOP is modeled to simulate auxiliaries consumption, pressure drops and components operating conditions. The model allows studying different operational strategies that maintain the power production during lifetime, minimizing efficiency losses; as well as to investigate the optimized operating setpoint of the plant at full load and during part-load operation.

The last section of the paper discusses the experimental results, through a complete analysis of the plant performance after plant startup, including energy and mass balances and allowing to validate the model. Cumulated indicators over the first nine months of operations regarding energy production, hydrogen consumption and efficiency are also discussed.

Commentary by Dr. Valentin Fuster
2018;():V001T07A006. doi:10.1115/ES2018-7344.

One of the biggest issues associated to Carbon Capture and Utilisation (CCU) applications involves the exploitation of the captured CO2 as a valuable consumable. An interesting application is the conversion of CO2 into renewable fuels via electrochemical reduction at high temperature. Still unexplored in the literature is the possibility of employing a Molten Carbonate Electrolysis Cell (MCEC) to directly converting CO2 and H2O into H2, CO and eventually CH4, if a methanation process is envisaged. The introduction of this concept into a reversible system — similarly to the process proposed with reversible solid-oxide cells — allows the creation of a cycle which oxidises natural gas to produce CO2 and then employs the same CO2 and excess renewable energy to produce renewable natural gas. The result is a system able to perform electrochemical storage of excess renewable energy (from wind or solar) and if/when required sell renewable natural gas to the grid.

In this work, a simulation of a reversible Molten Carbonate Cell (rMCC) is proposed. The reference MCFC technology considered is that from FuelCell Energy (USA) whose smaller stack is rated at 375 kW (DC). A simplified 0D stack model is developed and calibrated against experimental data. The Balance of Plant (BoP) is in common between the two operation modes MCFC and MCEC. In the former case, natural gas is electrochemically oxidised in the fuel compartment which receives carbonate ions (CO32−) from the air compartment, fed with air enriched with CO2 produced during electrolysis mode. The CO2 in the anode off gas stream is then purified and stored. In electrolysis mode, the stored CO2 is mixed with process H2O and sent to the fuel compartment of the MCEC; here, electrolysis and internal methanation occur. An external chemical reactor finalises the production of methane for either natural gas grid injection or storage and reuse in fuel cell mode. A thermodynamic analysis of the system is performed the yearly round-trip efficiency is assessed considering an assumed availability operating time of 7000 h/y. Finally, the overall green-house gas emission is assessed.

Commentary by Dr. Valentin Fuster
2018;():V001T07A007. doi:10.1115/ES2018-7456.

Flexible Li-ion batteries (LIBs) have a strong oncoming consumer market demand for use in wearable electronic devices, flexible smart electronics, roll-up displays, electronic shelf labels, active radio-frequency identification tags, and implantable medical devices. This market demand necessitates research and development of flexible LIBs in order to fulfill the power requirements of these next-generation devices. This study investigated the performance of quasi-solid anode — the active and conductive additive materials suspended in liquid electrolyte — for flexible lithium-ion batteries (LIB). A quasi-solid graphite anode was fabricated and tested using different material ratios and compositions, showing an acceptable performance. Furthermore, this study looked into the effect of graphite powder ratios in battery performance. A ratio of over 65% of the specific discharge capacity to the theoretical capacity was achieved maintaining the capacity retention of more than 74% after the second cycle.

Commentary by Dr. Valentin Fuster
2018;():V001T07A008. doi:10.1115/ES2018-7517.

Sodium thermal electrochemical converters (Na-TECs) offer a high efficiency advancement for converting thermal energy into electrical energy without moving parts. Since the cell operates using a Na pressure difference between the high temperature evaporator and the lower temperature condenser, a hermetic seal capable of maintaining that pressure difference is essential. This study looked at brazing of the ceramic electrolyte used in these cells, which is a β”-alumina solid-electrolyte referred to as BASE. Since a literature search found no papers pertaining to brazing of BASE, knowledge from ceramic to metal brazing called widegap brazing was used. Specifically, the widegap brazing of α-alumina to nickel-based alloys. Initial brazing trials used a traditional inert atmospheric brazing technique with an Ar-H2 gas mixture. However, the very low pO2 atmosphere resulted in the destruction of the BASE layers due to the diffusion of carbon to the outer surface of the electrolyte during brazing. A new and radically different brazing technique called air brazing was then attempted. This brazing technique proved successful using the brazing alloy Ag-8CuO. Both Ag and Cu are not deleteriously affected by Na corrosion; thus, Ag-8CuO were a good choice for the braze alloy. Leak tests were performed on these cells to establish their hermeticity. This cell structure and brazing technique proved to be successful. Air brazing is an exciting joining operation for these types of cells.

Commentary by Dr. Valentin Fuster
2018;():V001T07A009. doi:10.1115/ES2018-7539.

Tin (Sn) alloy electrodes show great potential for advancing battery performance due to the high capacity of tin. To realize this potential, the volumetric expansion during the lithiation process must be mitigated. One means of mitigating volumetric expansion of tin is to alloy it with copper to create Cu6Sn5. Such alloy electrodes retain some of the high capacity of tin, while attempting to accommodate volumetric changes with the addition of the malleable copper. Lithiation and delithiation tests were conducted with the Cu6Sn5 pellet electrodes to produce microstructural changes at the electrode surface. To observe and quantify these microstructural changes, x-ray microtomography was performed on electrode samples after electrochemical testing. The microtomography data was reconstructed into a 3D image, segmented, and the continuous phase size distribution (PSD) of each electrode sample was analyzed. The electrodes lithiated to 0 V vs Li/Li+ and then delithiated to 0.2 V vs. Li/Li+ showed the most substantial reduction in overall PSD compared to the other samples. This suggests that full lithiation of the Sn present in the alloy electrodes followed by partial delithiation of the Li4.4Sn to Li2CuSn can cause substantial microstructural changes related to volume expansion on lithiation and structural collapse upon delithiation. The electrodes fully lithiated to 0 V vs Li/Li+ and not delithiated show a higher overall phase size distribution, including all solid phases, than the pristine sample and the electrode samples that were partially lithiated to 0.2 V vs. Li/Li+ and delithiated to 1.5 V vs. Li/Li+. The higher overall phase size distribution that is shown by the sample that was fully lithiated and not delithiated is evidence of the significant volumetric expansion of the Cu6Sn5 compound due to lithiation. During this process of volumetric expansion, the phase size distribution of the Cu6Sn5/Sn phase is shown to decrease. When the volumetric expansion of the lithiated electrode samples and the volumetric contraction of the delithiated electrode sample are considered together, it can be inferred that the microstructural changes that are observed, such as the decrease in phase size distribution of the Cu6Sn5/Sn phase, can be attributed to the volumetric expansion and contraction of the compound during the lithiation and delithiation process.

Commentary by Dr. Valentin Fuster
2018;():V001T07A010. doi:10.1115/ES2018-7545.

This work addresses the development and construction of a sustainable alkaline membrane fuel cell (SAMFC). The SAMFC couples an alkaline membrane fuel cell (AMFC) with a hydrogen generation reactor that uses recycled aluminum from soda cans to split the water molecule through the oxidation of aluminum catalyzed by sodium hydroxide. An innovative cellulosic membrane supports the electrolyte, which avoids the undesirable characteristics of liquid electrolytes, and asbestos or ammonia that are substances that have been used to manufacture alkaline electrolyte membranes, which are knowingly toxic and carcinogenic. Aluminum is an inexpensive, abundant element in the earth’s crust and fully recyclable. Oxygen is supplied to the cell with atmospheric air that is pumped through a potassium hydroxide (KOH) aqueous solution in order to fix CO2, and in this way avoid potassium carbonate formation in order to keep the cell fully functional. A sustainable alkaline membrane fuel cell (SAMFC) system with one unitary cell, the reactor, and CO2 purifier was designed and built in the laboratory. The results are presented in polarization and power curves directly measured in the laboratory. Although recycled aluminum was used in the experiments, the results demonstrate that the cell was capable of delivering 0.9 V in open circuit and approximately 0.42 W of maximum power. The main conclusion is that by allowing for in situ sustainable hydrogen production, the SAMFC could eventually become economically competitive with traditional power generation systems.

Commentary by Dr. Valentin Fuster

Thermal and Mechanical Energy Storage

2018;():V001T08A001. doi:10.1115/ES2018-7161.

The use of pure biodiesel for compression ignition engines during the winter poses a challenge due to gelling and plugging of engine filters and fuel lines. The most common method to prevent this issue is blending with petroleum diesel and many engine manufacturers limit the biodiesel in blends to 20% or less for warrantee purposes; as low as 5% may be set for winter months. In a previous work, the authors proposed a novel fuel tank design that could potentially solve this problem and presented a numerical validation of the concept of using phase change materials (PCM) to enable cold weather operability of 100% biodiesel by maintaining its temperature above a cloud point of 5 degrees Celsius for over 3 days at an ambient temperature of −25 degrees Celsius and initial temperature of 20 degrees Celsius. In this research, an experimental analysis is performed using a scaled model of the fuel tank with canola oil as a test fluid in the tank. The tank is subjected to an ambient temperature of −20 degrees Celsius in an icing tunnel facility with air velocity at 10 m/s. The results show that the time above cloud point was increased from 18.6 hours to 22.5 and 33 hours respectively when 4 and 12 PCM tubes were inserted in the tank containing 33 litres of canola oil. A simple numerical model was formulated to predict the transient temperature of the oil and comparison with experimental results showed excellent agreement.

Commentary by Dr. Valentin Fuster
2018;():V001T08A002. doi:10.1115/ES2018-7326.

The design of the Latent Heat Thermal Storage System (LHTESS) was developed with thermal capacity of about 100 kWh as a part of small solar plant, based on the Organic Rankine Cycle (ORC). The phase change material (PCM) used is Solar salt with the melting/solidification temperature of about 220°C.

Thermo-physical properties of the PCM were measured, including its phase transition temperature, heat of fusion, specific heat and thermal conductivity. The design of the thermal storage was finalized by means of the 3-D CFD analysis.

The thermal storage system is made of six rectangular boxes with dimensions of 1 m (width) × 0.66 m (height) × 0.47 m (depth). The thermal energy is delivered to each of the thermal storage boxes with the use of thermal oil, heated by Fresnel mirrors. The heat is transferred into and from the PCM in the box using 40 bi-directional heat pipes with the external diameter of about 12 mm. The length of the heat pipe in the PCM box is 430 mm and it is placed in the cylindrical metallic protection cartridge, installed in the thermal storage vessel. The working fluid in the heat pipe is water. A set of metallic screens are installed in the box with the pitch of 8–10 mm to enhance the heat transfer from heat pipes to the PCM and vice-versa during the charging and discharging processes, which take about 4 hours.

The one unit of the described thermal storage system is undergoing the laboratory tests. Preliminary results demonstrate that the performance of the thermal storage is in a good agreement with numerical predictions. After completion of final design modifications, all units will be assembled at the plant’s demonstration site and tested with the ORC turbine.

Commentary by Dr. Valentin Fuster
2018;():V001T08A003. doi:10.1115/ES2018-7485.

Power overgeneration by renewable sources combined with less dispatchabe conventional power plants introduce the power grid to a new challenge, i.e., instability. The stability of the power grid requires constant balance between generation and demand. A well-known solution to power overgeneration is grid-scale energy storage. Although different energy storage technologies have been tested and demonstrated, reducing the cost of energy storage remains as a challenging goal for researchers, industries, and governments. Compressed Air Energy Storage (CAES) has been utilized for grid-scale energy storage for a few decades. However, conventional diabatic CAES systems are difficult and expensive to construct and maintain due to their high pressure operating condition. Hybrid Compressed Air Energy Storage (HCAES) systems are introduced as a new variant of old CAES technology to reduce the cost of energy storage using compressed air. The HCAES system split the received power from the grid into two subsystems. A portion of the power is used to compress air, as done in conventional CAES systems. The rest of the electric power is converted to heat in a high-temperature Thermal Energy Storage (TES) component using Joule heating. In this study, a solid-state grid-tied TES system is designed to operate with a HCAES system. The storage medium is considered to be high-temperature refractory concrete. The thermal energy is generated inside the concrete block using resistive heaters (wires) that are buried inside a concrete block. A computational approach was adopted to investigate the performance of the proposed TES system during a full charge/storage/discharge cycle. It was shown that the proposed design can be used to receive 200 kW of power from the grid for 6 hours without overheating the resistive heaters. The discharge computations show that the proposed geometry of the TES, along with a control strategy for the flow rate can provide a 74-kW micro-turbine of the HCAES with the minimum required temperature, i.e., 1144K at 0.6 kg/s of air flow rate for 6 hours. The computations were performed in ANSYS/FLUENT and the results were verified and validated using a grid independence study.

Commentary by Dr. Valentin Fuster
2018;():V001T08A004. doi:10.1115/ES2018-7503.

This paper presents a novel method of heat transfer enhancement and melting process expedition of phase change materials (PCMs) via silicone oil for the application in thermal energy storage systems. Sudden spot heating/cooling of the PCM causes a non-uniform melting process and in some cases the volume expansion/contraction. To avoid this malfunction, silicone oil can be applied in these systems to increase convective heat transfer (stirring effect). The feasibility of this method is investigated by two experimental analysis, one by having the mixture in a cylindrical container and one in a cubic container. The results from the images taken by Charge-Coupled Device (CCD) camera in the first analysis show a uniform melting process of the PCM. In the second analysis, the comparison is made for the two parallel setups with and without the silicone oil with the same operating conditions. The results show that in the system that lacks silicone oil, the paraffin starts melting after around 11 minutes from the heater start-up, while this time is around 6 minutes in the system with silicone oil. The effectiveness of silicone oil in enhancing the heat transfer rate is shown by a temperature rise of around 10 °C in the container. Applying PCMs in conjunction with silicone oil in various thermal storage systems for heating/cooling applications specifically in solar thermal collectors, enables heat transfer enhancement and consequently heat storage directly on the system.

Commentary by Dr. Valentin Fuster
2018;():V001T08A005. doi:10.1115/ES2018-7512.

The working principle and performance of thermochemical batteries have been studied before [1–3]. In this paper, the performance of a thermochemical battery based on magnesium chloride and ammonia pair with a constant mass flow rate of ammonia gas is studied. It is shown that controlling the mass flow rate lowers the temperature of the reactive complex and increases the duration of the absorption process. However, it was observed that the reaction becomes mass transfer limited which slows the absorption rate and takes control of the reaction away from the mass flow controller. The progress of the reaction inside the reactor is studied in a single-cell reactor to understand the performance of these thermal batteries. It was shown that a reaction zone starts at the inlet and moves toward the end of the reactor. The mass transfer limited reaction zone movement reduces the absorption rate and temperature in the reaction zone.

Commentary by Dr. Valentin Fuster

Sustainable Building Energy Systems

2018;():V001T09A001. doi:10.1115/ES2018-7130.

Recent developments in the Weather Research and Forecasting (WRF) Model have made it possible to accurately approximate solar power through the implementation of WRF-Solar. This study couples the WRF-Solar module with a multilayer urban canopy and building energy model in New York City (NYC) to create a unified WRF forecasting model called uWRF-Solar. Hourly time resolution forecasts are validated against ground station data collected at eight different sites. The validation is carried out independently for two different sky conditions: clear and cloudy. Results indicate that the uWRF-Solar model can forecast solar irradiance considerably well for the global horizontal irradiance (GHI) with an R squared value of 0.93 for clear sky conditions and 0.76 for cloudy sky conditions. Results are further used to directly forecast solar power production in the NYC region, where a power evaluation is done at a city scale. The outputs show a gradient of power generation produced by the potential available solar energy on the entire uWRF-Solar grid. In total, for the month of July 2016, NYC had a city PV potential of 233 kW/day/m2 and 7.25 MWh/month/m2.

Topics: Solar energy , Cities
Commentary by Dr. Valentin Fuster
2018;():V001T09A002. doi:10.1115/ES2018-7131.

The main objective of this study is to identify how climate variability influences human comfort levels in tropical-coastal urban environments. San Juan Metro Metropolitan Area (SJMA) of the island of Puerto Rico was chosen as a reference point. Temperature and relative humidity are identified as key environmental variables to maintain human comfort level. A new Human Discomfort Index (HDI) using the key environmental variables based on environmental enthalpy is defined. This index is expanded to determine the energy required to maintain indoor human comfort levels and is compared to total electric energy consumption for the island of Puerto Rico. Regression analysis shows that both temperature and HDI are good indicators to predict total electrical energy consumption. Results showed that over the past 35 years the average environmental enthalpy have increased, resulting in the increase of average HDI for SJMA. Surface weather station data further shows clear indication of urbanization biases ramping up the HDI. Long-term local scale (weather station; 30-years record) data shows a decreasing rate of maximum cooling per capita at −11.41 kW-h/years, and increasing of minimum cooling per capita of 10.64 kW-h/years. This contrasts with regional scale data for the whole Caribbean where increasing trends are observed for both minimum and maximum energy per capita. To estimate human comfort levels under extreme heat wave events conditions, an event of 2014 in the San Juan area was identified. The analysis is complemented by data from the National Center for Environmental Prediction (NCEP) at 250km spatial resolution, North American Regional Reanalysis (NARR) at 32 km spatial resolution, and simulations of the Weather Research and Forecasting model (WRF) at a resolution of 1 km, and by weather station data for San Juan. Model results were evaluated against observations showing good agreement for both temperature and relative humidity and improvements from the NCEP input. It also shows that Energy Per Capita (EPC), required to maintain indoor space at human comfort level, in urban areas during a heat wave event can increase to 21% as compared to normal day.

Topics: Cities , Climate
Commentary by Dr. Valentin Fuster

Solar Chemistry

2018;():V001T10A001. doi:10.1115/ES2018-7185.

This paper introduces a chemical-looping configuration integrated with a concentrating solar thermal (CST) system. The CST system uses an array of mirrors to focus sunlight, and the concentrated solar flux is applied onto a solar receiver to collect and convert solar energy into thermal energy. The thermal energy then drives a thermal power cycle for electricity generation or provides an energy source to chemical processes for material or fuel production. Considerable interest in CST has been driven by power generation with its capability to store thermal energy for continuous electricity supply or peak shaving. However, CST systems have other potential to convert solar energy into fuel or support thermochemical processes. The chemical-looping configuration integrated with the CST system can be a platform for implementing various solar-thermochemical processes. The chemical-looping configuration integrated with a CST system has potential applications for thermochemical energy storage and solar thermochemical hydrogen production. To use the solar energy efficiently and effectively, a high-temperature reactor receiver is a key component in the chemical-looping system. This paper shows a novel planar-cavity receiver design and its performance analyzed by solar-tracing and thermal-modeling methods for solar integration in a CST system.

Commentary by Dr. Valentin Fuster
2018;():V001T10A002. doi:10.1115/ES2018-7187.

Hydrogen generation in solar photoelectrochemical reactors could provide an important contribution to future energy regimes by storing intermittent renewable energy in a versatile energy vector. Using waste water as electron donor potentially facilitates economic operation. Here, organic contaminants instead of water are oxidised at the anode and two products of value are obtained simultaneously: hydrogen and clean water. Three different reactor concepts were compared in terms of ohmic losses. Based on the results of the simplified analysis a novel planar and scalable solar reactor with an aperture area of 368 cm2 was developed. It features a perforated photocathode and a non-perforated photoanode, both cold gas sprayed, in tandem arrangement and accepts electrolyte temperatures of up to 80°C. Confirmed by ray-tracing simulations the slit design of the photocathode allows homogeneous illumination of the two involved photoelectrodes with DLR’s test platform SoCRatus (Solar Concentrator with a Rectangular Flat Focus). The photocathode compartment and the photoanode compartment are separated by a membrane. Thus, the membrane being located in the optical path has to show sufficiently high transparency for solar light, particularly in the UV-Vis range. A 1,418 h aging study was performed in order to assess the optical performance of a Nafion™ membrane N1110 exposed to an aqueous mixture at 80°C, which contained 10 vol.-% methanol as a model substance for organic contaminants and sulfuric acid to adjust pH 3. It could be verified that the membrane maintains high transparency in the considered wavelength region from 280 nm to 1,100 nm which suggests the feasibility of the reactor concept. The design electrolyte flow of 2.5 l/min through each of the two reactor chambers practically allows isothermal operation on the SoCRatus under 17.5-fold concentrated irradiation. The inlet and outlet geometry of the reactor aims at uniform flow patterns, a low pressure drop as well as effective product gas transport and was optimised for automatic manufacturing. Reference electrodes and temperature sensors are incorporated directly in the reactor body for extended analysis and operation options. The parts of the reactor ensure compatibility with a wide range of waste waters and involved chemicals as well as mechanical stability. Moreover, they are resistant to light exposure and weathering.

Commentary by Dr. Valentin Fuster

Concentrated Solar Power

2018;():V001T11A001. doi:10.1115/ES2018-7136.

A scheme to streamline the electric power generation profile of concentrating solar power plants of the parabolic trough collector type is suggested. The scheme seeks to even out heat transfer rates from the solar field to the power block by splitting the typical heat transfer fluid loop into two loops using an extra vessel and an extra pump. In the first loop, cold heat transfer fluid is pumped by the cold pump from the cold vessel to the solar field to collect heat before accumulating in the newly introduced hot vessel. In the second loop, hot heat transfer fluid is pumped by the hot pump from the hot vessel to a heat exchanger train to supply the power block with its heat load before accumulating in the cold vessel. The new scheme moderately decouples heat supply from heat sink allowing for more control of heat delivery rates thereby evening out power generation.

Commentary by Dr. Valentin Fuster
2018;():V001T11A002. doi:10.1115/ES2018-7166.

One direct absorption receiver concept currently investigated at the DLR is the Centrifugal Particle Receiver (CentRec®). Successful tests and promising results of this receiver design have been achieved in a Proof-of-Concept scale with 7.5 kW thermal power and 900°C particle temperature in 2014. Based on these results the prototype has been scaled up to 2.5 MW thermal power for a future pilot plant. Lab tests have been carried out with infrared heaters. In a next step the prototype has been prepared to be tested on-sun in a test setup in the Juelich Solar Tower, Germany. The tests aim to demonstrate high temperature operation and to evaluate the performance of the system.

The test setup consists of a centrifugal receiver integrated into the tower and a closed loop particle transport system. The transport system includes an air cooling system to cool down the particles at the receiver outlet, cold particle storage, belt bucket elevator, hopper and particle metering system. While the 2.5 MWth receiver prototype has been developed in a former project, the further infrastructure for the on-sun tests needed to be designed, manufactured and installed. The system is equipped with measurement instrumentation, data acquisition system and control software. Manufacturing of all main components has been completed. Installation of the test setup started in November 2016 and finished in June 2017. Cold and hot commissioning have been carried out from July 2017 until September 2017. On-sun tests started in September 2017. Receiver tests up to 775°C/1,430°F receiver outlet temperature and more than 900°C/1,650°F particle temperature in the receiver have already been achieved. Tests up to 900°C particle outlet temperature are planned at different load levels and will be conducted until summer 2018.

This paper describes the test setup for a centrifugal particle receiver system, presenting design, installation and commissioning of the system. It presents test results of first on-sun tests and gives an outlook on further steps regarding solar tests planned for 2018.

Commentary by Dr. Valentin Fuster
2018;():V001T11A003. doi:10.1115/ES2018-7415.

The light collection and concentration subsystem (LCCS) of any concentrating solar thermal (CST) system is composed of the surfaces that collect and concentrate the sunlight and of the input surfaces of the receivers, or receivers’ envelopes, where the light is concentrated. For all commercial CST technologies the LCCS is, together with the power block, the subsystem that has more influence in the overall performance and cost. Thus, its optimization is critical to increase the cost-competitiveness of these systems. This optimization requires, in many cases, the optimization of the position, geometry and size of a very large number of solar collecting and concentrating surfaces as well as the optimization of the shape and size of the input surfaces of the receivers where the sunlight is concentrated. Because a full optimization requires the exploration of a configuration space with a very large number of dimensions, the traditional approach consist in making many initial assumptions to drastically reduce the number of dimensions of the configuration space to a handful, so that the optimization can be carried out using conventional high-end workstations in a matter of hours.

However, to achieve relevant breakthroughs and to substantially increase the cost-competitiveness of CST systems a bolder approach is needed, where sophisticated design and analysis tools, engineered from the start to be used in High Performance Computers (HPC), will be combined with sophisticated optimization strategies targeted to explore and find optimal solutions in very high dimensional configuration spaces.

This paper presents the first of a series of such design and analysis tools. The tool, call Flux Tracer, partitions the three-dimensional space in which the LCC subsystem under analysis is immersed into volumetric pixels (voxels) and computes the radiant energy flux that traverses each voxel as a function of time. It integrates the energy density in every voxel overtime, providing detailed information regarding how the radiant energy flows in space in a given LCC subsystem and in a given period of time. This information is the cornerstone of the highly sophisticated computational LCC subsystem optimization framework The Cyprus Institute (CYI) is developing, in collaboration with the Australian National University (ANU), targeted to be used in HPC’s.

Topics: Computers
Commentary by Dr. Valentin Fuster
2018;():V001T11A004. doi:10.1115/ES2018-7437.

Compared to Solar Photovoltaics (PV), Concentrated Solar Power (CSP) can store the excess solar thermal energy, extend the power generation at night and cloudy days, and levelize the mismatch between energy demand and supply. To make CSP competitive, Thermal Energy Storage (TES) system filled with phase change material (PCM) is a promising indirect energy storage technique, compared to the TES system using concrete or river rocks. It is of great interests to solar thermal community to apply the latent heat thermal energy storage (LHTES) system for large scale CSP application, because PCMs can store more thermal energy due to the latent heat during the melting/freezing process. Therefore, a comprehensive parametric analysis of LHTES system is necessary in order to improve its systematic performance, since LHTES system has a relatively low energy storage efficiency compared to TES systems using sensible materials.

In this study, an 11-dimensionless-parameter space of LHTES system was developed, by considering only the technical constraints (materials properties and operation parameters), instead of economic constraints. Then the parametric analysis was performed based on a 1D enthalpy-based transient model, and the energy storage efficiency was used as the objective function to minimize the number of variables in the parameter space. It was found that Stanton number (St), PCM radius (r), and void fraction (ε) are the three most important ones. The sensitivity study was conducted then based on the three dimensionless-parameter space which will significantly influence the system performance. The results of this study make LHTES system competitive with TES system using sensible materials in terms of energy storage efficiency.

Commentary by Dr. Valentin Fuster
2018;():V001T11A005. doi:10.1115/ES2018-7464.

Particle-based heat transfer fluids for concentrated solar power (CSP) tower applications offer a unique advantage over traditional fluids as they have the potential to reach very high operating temperatures. Our work studies the heat transfer behavior of dense granular flows through cylindrical tubes as a potential system configuration for CSP towers. Thus far, we have experimentally investigated the heat transfer to such flows. Our results corroborate the observations of other researchers; namely, that the discrete nature of the flow limits the heat transferred from the tube wall to the flow due to an increased thermal resistance in the wall-adjacent layer. The present study focuses on this near-wall phenomenon, examining how it varies with system configuration and flow rate. A correlation to predict the thermal resistance, in the form of an effective thermal conductivity, was developed based on the underlying physics controlling the heat transfer. The model developed focuses on heat transfer via conduction, considering the heat transfer to particles in contact with the wall, heat transfer to particles not in contact with the wall, and heat transfer through the void spaces. Discrete Element Method simulations were used to examine the flow parameters necessary to understand the heat transfer in the wall-adjacent layer, in particular the packing fraction in the wall-adjacent layer and the number of particle-wall contacts. Incorporation of the model into the single-resistance model developed by Sullivan & Sabersky [1] showed good agreement with their experimental results and those of Natarajan & Hunt [2].

Commentary by Dr. Valentin Fuster
2018;():V001T11A006. doi:10.1115/ES2018-7502.

Development is underway for modifications to an existing central receiver power tower concentrator solar power research facility to accommodate a new solar chemical test module. Optical analysis, using Sol Trace, is done to model the existing heliostat field, general tower geometry, and planned system layout to predict the incident irradiation to the new experimental receiver called the Solar Reducer Receiver Reactor (SR3). Within the SR3, a layer of particles flowing over an inclined plane will be highly irradiated to chemically reduce the particulate. To accommodate the inclined plane reactor geometry, a beam down mirror will be modeled. An estimated 1000 suns will be required at the aperture. Currently, the field typically provides around 300 suns over a 1 m × 1 m area. To achieve the required higher flux, a secondary concentrator will concentrate the irradiation from a larger area into a smaller focal spot. Rather than using an expensive compound parabolic design, a series of flat plate petals will instead be used to create a cost effective secondary. The flat plate design also provides added benefits for ease of installation, manufacturing, and cooling. The ray tracing model is used to compare several design parameters including the number of petals, petal length, aperture size and the inclination angle of the petals for the secondary.

With these parameters selected, designs have been created for a test module to be constructed at King Saud University’s Riyadh Techno Valley CSP Tower. Additionally, the model is used to estimate the necessary cooling needed to operate both the secondary concentrator and the beam down mirror. These models will be tested experimentally using several quartz heaters. The beam down will be cooled by forced convection air, while the secondary concentrator will use water cooling. Lab experiments will measure the feasibility and effectiveness of the proposed cooling before construction. Once these proof of concepts tests have been completed, construction of the secondary concentrator and beam down mirror will begin to allow for testing in 2018.

Commentary by Dr. Valentin Fuster
2018;():V001T11A007. doi:10.1115/ES2018-7504.

This paper presents an evaluation of alternative particle heat-exchanger designs, including moving packed-bed and fluidized-bed designs, for high-temperature heating of a solar-driven supercritical CO2 (sCO2) Brayton power cycle. The design requirements for high pressure (≥ 20 MPa) and high temperature (≥ 700 °C) operation associated with sCO2 posed several challenges requiring high-strength materials for piping and/or diffusion bonding for plates. Designs from several vendors for a 100 kW-thermal particle-to-sCO2 heat exchanger were evaluated as part of this project. Cost, heat-transfer coefficient, structural reliability, manufacturability, parasitics and heat losses, scalability, compatibility, erosion and corrosion, transient operation, and inspection ease were considered in the evaluation. An analytical hierarchy process was used to weight and compare the criteria for the different design options. The fluidized-bed design fared the best on heat transfer coefficient, structural reliability, scalability and inspection ease, while the moving packed-bed designs fared the best on cost, parasitics and heat losses, manufacturability, compatibility, erosion and corrosion, and transient operation. A 100 kWt shell-and-plate design was ultimately selected for construction and integration with Sandia’s falling particle receiver system.

Commentary by Dr. Valentin Fuster
2018;():V001T11A008. doi:10.1115/ES2018-7505.

A sodium thermal electrochemical converter (Na-TEC) converts heat directly into electricity without moving parts by isothermal expansion of ions through beta”-alumina solid-electrolyte (BASE). These generators are most similar to thermoelectric generators; however, they are considerably more efficient than the best performing thermoelectric materials. While these heat engines have been considered for CSP applications, literature review found that the efficiency of single-stage Na-TEC could readily achieve 20% even though ideal cycle efficiencies predict above 45% efficiency at elevated temperatures. Thermal parasitic loss has been identified to be responsible for the largest drop in the efficiency. Our recent study shows that staging helps to improve thermal management of the Na-TEC, due to the lower average temperature of the device, which can reduce the thermal parasitic loss. We demonstrate that dual-stage device can improve the efficiency by up to 8% over the best performing single-stage device. We are currently designing and developing a modular dual-stage Na-TEC power block with target efficiency of 33%. We emphasize modularity because this power block can be potentially deployed for both small-scale dish solar, which is appropriate for distributed residential scale (2–3 kWe), and large-scale heliostats and parabolic trough CSP, which is appropriate for centralized industrial scale. A fundamental cost-scaling relationship for this technology was developed based on this design. System variables and component manufacturing methods with material selection for processes were established. The current off-the-shelf component costs indicated an overnight capital cost of $2,044/kWe. The costs of BASE, manufacturing, and electrode preparation have driven the overall price of the module. The paper demonstrates $/W design optimization and cost scaling analysis to reduce the system capital $/W metric below $ 1,500/kWe, with the goal being to achieve the cost target of <900/kWe set by Department of Energy’s Sun Shot Initiative.

Commentary by Dr. Valentin Fuster
2018;():V001T11A009. doi:10.1115/ES2018-7543.

Prior research at Sandia National Laboratories showed the potential advantages of using light-trapping features which are not currently used in direct tubular receivers. A horizontal bladed receiver arrangement showed the best potential for increasing the effective solar absorptance by increasing the ratio of effective surface area to the aperture footprint. Previous test results and models of the bladed receiver showed a receiver efficiency increase over a flat receiver panel of ∼ 5–7% over a range of average irradiances, while showing that the receiver tubes can withstand temperatures > 800 °C with no issues.

The bladed receiver is being tested at various peak heat fluxes ranging 75–150 kW/m2 under transient conditions using Air as a heat transfer fluid at inlet pressure ∼250 kPa (∼36 psi) using a regulating flow loop. The flow loop was designed and tested to maintain a steady mass flow rate for ∼15 minutes using pressurized bottles as gas supply. Due to the limited flow-time available, a novel transient methodology to evaluate the thermal efficiencies is presented in this work. Computational fluid dynamics (CFD) models are used to predict the temperature distribution and the resulting transient receiver efficiencies. The CFD simulations results using air as heat transfer fluid have been validated experimentally at the National Solar Thermal Test Facility in Sandia National Labs.

Commentary by Dr. Valentin Fuster
2018;():V001T11A010. doi:10.1115/ES2018-7597.

Developing small scale turbines pauses challenges in terms of increased stresses due to high rotational speed leading to increase in component thicknesses and turbine overall weight. Therefore this study assesses both; the structural and aerodynamic performance of a Small Scale Radial Turbine SSRT by integrating finite-element methods FEM and Computational Fluid Dynamic CFD. Using Vista preliminary design model in ANSYS and detailed 3D CFD optimization, SSRT with 1–5 kW power for solar powered Brayton cycle was developed with high efficiency of 89.2%. Then both; the turbine’s hub and blades were structurally analysed under various loading conditions to investigate the effect of various rotational speeds and blade shapes on the stress distribution and deformation of the blades. The results of the current study showed that a maximum increment of 65% stress and 57% deformation was noticed when reaching the maximum studied rotational speed at inlet air temperature of 450 K.

Commentary by Dr. Valentin Fuster


2018;():V001T12A001. doi:10.1115/ES2018-7121.

The main purpose of this study is to investigate the feasibility of using a hybrid photovoltaic (PV), fuel cell (FC) and battery system to power different load cases, which are intended to be used at Al-Zarqa governorate in Jordan. All aspects related to the potentials of solar energy in Al-Hashemeya area were studied. The irradiation levels were carefully identified and analyzed, and found to range between 4.1–7.6 kWh/m2/day; these values represented an excellent opportunity for the photovoltaic solar system. Various renewable and non-renewable energy sources, energy storage methods and their applicability regarding cost and performance are discussed, in which HOMER (Hybrid Optimization for Electric Renewable) software is used as a sizing and optimization tool. Different scenarios with Photovoltaic slope, diesel price, and fuel cell cost were done. A remote residential building, school and factory having an energy consumption of 31 kWh/day with a peak of 5.3 kW, 529 kWh/day with a maximum of 123 kW and 608 kWh/day with a maximum of 67 kW respectively, were considered as the case studies’ loads. It was found that the PV-diesel generator system with battery is the most suitable solution at present for the residential building case, while the PV-FC-diesel generator-electrolyzer hybrid system with battery suites best both the school and factory cases.

The load profile for each case was found to have a substantial effect on how the system’s power produced a scheme. For the residential building, PV panels contributed by about 75% of the total power production, the contribution increased for the school case study to 96% and dropped for the factory case to almost 50%.

Topics: Fuel cells , Batteries
Commentary by Dr. Valentin Fuster
2018;():V001T12A002. doi:10.1115/ES2018-7227.

A planar perovskite solar cell (PSC) with p-i-n inverted structure was modeled and simulated to determine the power output characteristics under illumination. The performance of inverted PSC device was correlated to the thickness of the absorber layer, band alignment, and electrical properties of the hole transport materials (HTMs). Our simulation indicates that, with an optimized absorber layer thickness ∼300 nm, an efficiency of 18% can be achieved. This baseline device was further utilized to investigate the role of band offset between the HTM and absorber layer. Results show that the device efficiency can be improved to 24% when the work function of HTM is reduced to 0.1 eV lower than the valence band edge of perovskite. Parametric studies were carried out to compare the feasibility of five different HTMs including spiro-OMeTAD, Cu2O, CuSCN, NiO, and CuI. Among them, NiO is the most promising candidate with a theoretical efficiency limit up to 27%. This work would serve as a modeling frame to simulate and interpret the performance of inverted PSCs and suggest further device optimization strategies.

Commentary by Dr. Valentin Fuster
2018;():V001T12A003. doi:10.1115/ES2018-7533.

Thin film solar cells (TFSC) differ from the conventional wafer solar cell panels in that they are a fraction of the thickness, hence they boast reduced material costs, lighter weight, and possible flexibility. To improve their light-trapping and absorption efficiency, manufacturers currently use nanometer scale texturing. When manufacturing nano textured thin film solar cells in the substrate configuration, the back reflector is also textured. It has been observed that a textured back reflector leads to parasitic light absorption in silicon solar cells. This occurrence reduces the back reflector effectiveness, and thus reduces absorption in the absorber layer and overall efficiency. However, there is little to no similar research done for thin film (CdTe/CdS) solar cells devices. In this work, wave optical analyses of thin film CdTe/CdS solar cells with and without nano texturing on the metal back reflectors were simulated using ANSYS ANSOFT High Frequency Structural Simulator (HFSS). The optical analyses yielded percentage absorptions for unit cells with four absorber thicknesses range between 250- to 1000 nm, with and without a textured back reflector over six wavelengths range from 360nm to 860 nm, and with 3 different back contact metals (Au, Ag, and Al). It was noted that the textured back contacts show a substantial increase in the absorption in the active CdTe layer in the infrared range. Additionally, back reflector texturing increases the parasitic absorption in the metal back reflector layer as well, especially with ultrathin absorber layer. It was also found that additional parasitic absorption due to a textured back reflector has less of an impact on absorption as the active absorber thickness increases to 500 nm, 750 nm, or 1000 nm. Finally, silver (Ag) as back contact outperforms both aluminum (Al) and gold (Au). This finding might be crucial to solar cell manufacturers because it could possibly be an overlooked factor in achieving higher efficiencies for relatively thin cells.

Commentary by Dr. Valentin Fuster
2018;():V001T12A004. doi:10.1115/ES2018-7569.

In this study, an efficient cooling technique for concentrator photovoltaic (CPV) cells is proposed to enhance the system electrical efficiency and extend its lifetime. To do this, a comprehensive three-dimensional conjugate heat transfer model of CPV cells layers coupled with the heat transfer and fluid flow model inside jet impingement heat sink is developed. Four different jet impingement designs are compared. The investigated designs are (A) central inlet jet, (B) Hypotenuse inlet jet, (C) staggered inlet jet, and (D) conventional jet impingement design with side drainage. The effect of coolant flowrate on the CPV/T system performance is investigated. The model is numerically simulated and validated using the available experiments. The performance of CPV system is investigated at solar concentration ratios of 20 and coolant flowrate up to 6000g/min. It is found that increasing the flowrate from 60 g/min to 600 g/min decrease the maximum cell temperature by 31°C for the configuration D while increasing the flowrate from 600 g/min to 6000 g/min reduce the cell temperature by 20.2°C. It is also concluded that at a higher flowrate of 6000g/min, all the investigated configurations relatively achieve better temperature uniformity with maximum temperature differences of 0.9 °C, 2.1 °C, 3.6 °C, and 3.9 °C for configurations A, B, C, and D respectively.

Commentary by Dr. Valentin Fuster

Wind Energy Systems and Technologies

2018;():V001T13A001. doi:10.1115/ES2018-7322.

This study uses Large Eddy Simulation in the ANSYS Fluent software to assess the accuracy of the forced cooling term for the overhead conductor codes, IEEE 738 [1] and CIGRÉ 207 [2], for Real Time Thermal Rating of a wind farm power line. The analysis is done for low wind speed, corresponding to Reynolds Number of 3,000. The primary goal is to calculate Nusselt Number for cylindrical conductors with free-stream turbulence. Calculations showed an increase in convective heat transfer from the low turbulence value by ∼ 30 % at turbulence intensity of 21% and length scale to diameter ratio of 0.4; and an increase of ∼ 19 % at turbulence intensity of 8% and length scale to diameter ratio of 0.4.

Commentary by Dr. Valentin Fuster
2018;():V001T13A002. doi:10.1115/ES2018-7357.

This paper proposes a new combined vibration suppressing device, which can be used to suppress the swaying vibration of off-shore floating wind generator under waves. The floating wind power station tower was modeled, the wave force and the torsion force of the tower were analyzed and the FSI numerical simulation was carried out. The calculation results demonstrate that the amplitudes of the tower torsion angle have been attenuated by 8%, 11% and 17% with different vibration suppression devices which are TMD, TLD and new combined device. In this case the new combined device has the best vibration suppression performance. It is validated that compared to the other two single vibration suppression devices, the new combined device has better vibration suppression capacity and a new way is provided to design the vibration suppression device for off shore floating wind power station.

Commentary by Dr. Valentin Fuster

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