Exergoeconomic analysis of a vehicular PEM fuel cell system

In this study, we deal with the exergoeconomic analysis of a proton exchange membrane (PEM) fuel cell power system for transportation applications. The PEM fuel cell performance model, that is the polarization curve, is previously developed by one of the authors by using the some derived and developed equations in literature. The exergoeconomic analysis includes the PEM fuel cell stack and system components as compressor, humidifiers, pressure regulator and the cooling system. A parametric study is also conducted to investigate the system performance and cost behaviour of the components, depending on the operating temperature, operating pressure, membrane thickness, anode stoichiometry and cathode stoichiometry. For the system performance, energy and exergy efficiencies and power output are investigated in detail. It is found that with an increase of temperature and pressure and a decrease of membrane thickness the system efficiency increases which leads to a decrease in the overall production cost. The minimization of the production costs is very crucial in commercialization of the fuel cells in transportation sector.     

PEM fuel cell performance with solar air preheating

Proton Exchange Membrane Fuel Cells (PEMFC) have proven to be a promising energy conversion technology in various power applications and since it was developed, it has been a potential alternative over fossil fuel-based engines and power plants, all of which produce harmful by-products. The inlet air coolant and reactants have an important effect on the performance degradation of the PEMFC and certain power outputs. In this work, a theoretical model of a PEM fuel cell with solar air heating system for the preheating hydrogen of PEM fuel cell to mitigate the performance degradation when the fuel cell operates in cold environment, is proposed and evaluated by using energy analysis. Considering these heating and energy losses of heat generation by hydrogen fuel cells, the idea of using transpired solar collectors (TSC) for air preheating to increase the inlet air temperature of the low-temperature fuel cell could be a potential development. The aim of the current article is applying solar air preheating for the hydrogen fuel cells system by applying TSC and analyzing system performance. Results aim to attention fellow scholars as well as industrial engineers in the deployment of solar air heating together with hydrogen fuel cell systems that could be useful for coping with fossil fuel-based power supply systems.     

Fuel cell energy generation and recovery cycle analysis for residential application

Today’s concern regarding limited fossil fuel resources and their contribution to environmental pollution have changed the general trend to utilization of high efficiency power generation facilities like fuel cells. According to annual reducing capital cost of these utilities, their entrance to commercial level is completely expected. Hot exhaust gases of Solid Oxide Fuel Cells (SOFC) are potentially applicable in heat recovery systems. In the present research, a SOFC with the capacity of 215 kW has been combined with a recovery cycle for the sake of simultaneous of electric power, cooling load and domestic hot water demand of a hotel with 4600 m² area. This case study has been evaluated by energy and exergy analysis regarding exergy loss and second law efficiency in each component. The effect of fuel and air flow rate and also current density as controlling parameters of fuel cell performance have been studied and visual software for energy-exergy analysis and parametric study has been developed. At the end, an economic study of simultaneous energy generation and recovery cycle in comparison with common residential power and energy systems has been done. General results show that based on fuel lower heating value, the maximum efficiency of 83 percent for simultaneous energy generation and heat recovery cycle can be achieved. This efficiency is related to typical climate condition of July in the afternoon, while all the electrical energy, cooling load and 40 percent of hot water demand could be provided by this cycle. About 49 percent of input exergy can be efficiently recovered for energy requirements of building. Generator in absorption chiller and SOFC are the most destructive components of exergy in this system.     

Performance assessment of a solar hydrogen and electricity production plant using high temperature PEM electrolyzer and energy storage

This paper investigates the performance of a high temperature Polymer Electrolyte Membrane (PEM) electrolyzer integrated with concentrating solar power (CSP) plant and thermal energy storage (TES) to produce hydrogen and electricity, concurrently. A finite-time-thermodynamic analysis is conducted to evaluate the performance of a PEM system integrated with a Rankine cycle based on the concept of exergy. The effects of solar intensity, electrolyzer current density and working temperature on the performance of the overall system are identified. A TES subsystem is utilized to facilitate continuous generation of hydrogen and electricity. The hydrogen and electricity generation efficiency and the exergy efficiency of the integrated system are 20.1% and 41.25%, respectively. When TES system supplies the required energy, the overall energy and exergy efficiencies decrease to 23.1% and 45%, respectively. The integration of PEM electrolyzer enhances the exergy efficiency of the Rankine cycle, considerably. However, it causes almost 5% exergy destruction in the integrated system due to conversion of electrical energy to hydrogen energy. Also, it is concluded that increase of working pressure and membrane thickness leads to higher cell voltage and lower electrolyzer efficiency. The results indicate that the integrated system is a promising technology to enhance the performance of concentrating solar power plants.     

Performance investigation of a transportation PEM fuel cell system

In this study, a comprehensive performance analysis of a transportation system powered by a PEM fuel cell engine system is conducted thermodynamically both through energy and exergy approaches. This system includes system components such as a compressor, humidifiers, pressure regulator, cooling system and the fuel cell stack. The polarization curves are studied in the modeling and compared with the actual data taken from the literature works before proceeding to the performance modeling. The system performance is investigated through parametric studies on energy, exergy and work output values by changing operating temperature, operating pressure, membrane thickness, anode stoichiometry, cathode stoichiometry, humidity, reference temperature and reference pressure. The results show that the exergy efficiency increases with increase of temperature from 323 to 353 K by about 8%, pressure from 2.5 to 4 atm by about 5%, humidity from 97% to 80% by about 10%, and reference state temperature from 253 to 323 K by about 3%, respectively. In addition, the exergy efficiency increases with decrease of membrane thickness from 0.02 to 0.005 mm by about 9%, anode stoichiometry from 3 to 1.1 by about 1%, and cathode stoichiometry from 3 to 1.1 by about 35% respectively.     

Performance assessment of a biogas fuelled molten carbonate fuel cell-thermophotovoltaic cell-thermally regenerative electrochemical cycle-absorption refrigerator-alkaline electrolyzer for multigenerational applications

In recent years, there has been increasing interest in fuel cell hybrid systems. In this paper, a novel multi-generation combined energy system is proposed. The system consists of a molten carbonate fuel cell (MCFC), a thermally regenerative electro-chemical cycle (TREC), a thermo photovoltaic cell (TPV), an alkaline electrolyzer (AE) and an absorption refrigerator (AR). It has four useful outputs, namely electricity, hydrogen, cooling and heating. The overall system is thermodynamically modeled in a detailed manner while its simulation and modeling are done through the TRNSYS software tool. Power output, cooling-heating and produced hydrogen rates are determined using energetic and exergetic analysis methods. Results are obtained numerically and plotted. The maximum power output from the system is 16.14 kW while maximum energy efficiency and exergy efficiency are 86.8% and 80.4%,. The largest exergy destruction is due to the MCFC.     

Solar-powered regenerative PEM electrolyzer/fuel cell system

An electrolyzer/fuel cell energy storage system is a promising alternative to batteries for storing energy from solar electric power systems. Such a system was designed, including a proton-exchange membrane (PEM) electrolyzer, high-pressure hydrogen and oxygen storage, and a PEM fuel cell. The system operates in a closed water loop. A prototype system was constructed, including an experimental PEM electrolyzer and combined gas/water storage tanks. Testing goals included general system feasibility, characterization of the electrolyzer performance (target was sustainable 1.0 A/cm² at 2.0 V per cell), performance of the electrolyzer as a compressor, and evaluation of the system for direct-coupled use with a PV array. When integrated with a photovoltaic array, this type of system is expected to provide reliable, environmentally benign power to remote installations. If grid-coupled, this system (without PV array) would provide high-quality backup power to critical systems such as telecommunications and medical facilities.     

Energy and exergy analyses of hydrogen production via solar-boosted ocean thermal energy conversion and PEM electrolysis

Energy and exergy analyses are reported of hydrogen production via an ocean thermal energy conversion (OTEC) system coupled with a solar-enhanced proton exchange membrane (PEM) electrolyzer. This system is composed of a turbine, an evaporator, a condenser, a pump, a solar collector and a PEM electrolyzer. Electricity is generated in the turbine, which is used by the PEM electrolyzer to produce hydrogen. A simulation program using Matlab software is developed to model the PEM electrolyzer and OTEC system. The simulation model for the PEM electrolyzer used in this study is validated with experimental data from the literature. The amount of hydrogen produced, the exergy destruction of each component and the overall system, and the exergy efficiency of the system are calculated. To better understand the effect of various parameters on system performance, a parametric analysis is carried out. The energy and exergy efficiencies of the integrated OTEC system are 3.6% and 22.7% respectively, and the exergy efficiency of the PEM electrolyzer is about 56.5% while the amount of hydrogen produced by it is 1.2 kg/h.     

Performance analysis of a PEM fuel cell unit in a solar–hydrogen system

In this paper, energy and exergy analyses for a 1.2 kWp Nexa PEM fuel cell unit in a solar-based hydrogen production system is undertaken to investigate the performance of the system for different operating conditions using experimental setup and thermodynamic model. From the model results, it is found that there are reductions in energy and exergy efficiencies (about 14%) with increase in current density. These are consistent with the experimental data for the same operating conditions. A parametric study on the system and its parameters is undertaken to investigate the changes in the efficiencies for variations in temperature, pressure and anode stoichiometry. The energy and exergy efficiencies increase with pressure by 23% and 15%, respectively. No noticeable changes are observed in energy and exergy efficiencies with increase in temperature. The energy and exergy efficiencies decrease with increase in anode stoichiometry by 17% and 14%, respectively. These observations are reported for the given range of current density as 0.047–0.4 A/cm². The results and analyses show that the PEM fuel-cell system has lower exergy efficiencies than the corresponding energy efficiencies due to the irreversibilities that are not considered by energy analysis. In comparison with experimental data, the model is accurate in predicting the performance of the proposed fuel-cell system. The parametric and multivariable analyses show that the option of selecting appropriate set of conditions plays a significant role in improving performance of existing fuel-cell systems.     

Energetic and exergetic analyses of a combined system consisting of a high-temperature polymer electrolyte membrane fuel cell and a thermoelectric generator with Thomson effect

A combined system model consisting of a high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC), a regenerator and a thermoelectric generator (TEG) is proposed, where the TEG is applied to harness the generated waste heat in the HT-PEMFC for extra electricity production. The TEG considers not only the Seebeck effect and Peltier effect but also the Thomson effect. The mathematical expressions of power output, energy efficiency, exergy destruction rate and exergy efficiency for the proposed system are derived. The energetic and exergetic performance characteristics for the whole system are revealed. The optimum operating ranges for some key performance parameters of the combined system are determined using the maximum power density as the objective function. The combined system maximum power density and its corresponding energy efficiency and exergy efficiency allow 19.1%, 12.4% and 12.6% higher than that of a stand-alone HT-PEMFC, while the exergy destruction rate density is only increased by 8.6%. The system performances are compared between the TEG with and without the Thomson effect. Moreover, the impacts of comprehensive parameters on the system performance characteristics are discussed. The obtained results are helpful in developing and designing such an actual combined system for efficient and clean power production.     

Exergy analysis of a regional-distributed PEM fuel cell system

In this paper, the exergy flow and exergy efficiency of a 3 kW proton-exchange-membrane fuel cell were investigated, and the regional characteristic of the distributed energy system was considered. In the environmental temperature range of 263–313 K, the difference in the total efficiency of the proposed system was 6%. On the other hand, the difference in the exergy total efficiency of the same temperature range was 30%. Moreover, as a result of examining how to improve the exergy efficiency of this system, certain improvement methods were proposed: (a) preheat the city-gas and air supplied to the system using exhaust heat and raise the combustion temperature; (b) preheat the water supplied to the system using exhaust heat; (c) change the catalyst material of each unit and reduce the amount of cooling of the reformed gas; and (d) examine the combined cycle power generation. The exergy efficiency, in the case of introducing the proposed system into individual homes in Sapporo, Tokyo, and Kagoshima, was evaluated. Consequently, when the system was introduced into a community with low outside air temperatures, exergy efficiency increased compared with communities with high outside air temperatures.     

Evaluation of a new geothermal based multigenerational plant with primary outputs of hydrogen and ammonia

Increasing environmental concerns and decreasing fossil fuel sources compel engineers and scientists to find resilient, clean, and inexpensive alternative energy options Recently, the usage of renewable power resources has risen, while the efficiency improvement studies have continued. To improve the efficiency of the plants, it is of great significance to recover and use the waste heat to generate other useful products. In this paper, a novel integrated energy plant utilizing a geothermal resource to produce hydrogen, ammonia, power, fresh water, hot water, heated air for drying, heating, and cooling is designed. Hydrogen, as an energy carrier, has become an attractive choice for energy systems in recent years due to its features like high energy content, clean, bountiful supply, non-toxic and high efficiency. Furthermore in this study, hydrogen beside electricity is selected to produce and stored in a hydrogen storage tank, and some amount of hydrogen is mixed with nitrogen to compound ammonia. In order to determine the irreversibilities occurring within the system and plant performance, energy and exergy analyses are then performed accordingly. In the design of the plant, each sub-system is integrated in a sensible manner, and the streams connecting sub-systems are enumerated. Then thermodynamic balance equations, in terms of mass, energy, entropy and exergy, are introduced for each unit of the plant. Based on the system inputs and outputs, the energy and exergy efficiencies of the entire integrated plant is found to be 58.68% and 54.73% with the base parameters. The second part of the analysis contains some parametric studies to reveal how some system parameters, which are the reference temperature, geothermal resource temperature and mass flow rate, and separator inlet pressure in the geothermal cycle, affect both energy and exergy efficiencies and hence the useful outputs.     

Exergy analysis of PEM fuel cells for marine applications

Fuel cells have a promising potential use in stationary and mobile power generation systems, as well as in automotive, aerospace or marine industries. At present, the main field of marine applications of fuel cells is submarines. Hydrogen/oxygen polymer electrolyte membrane (PEM) fuel cells are commonly used in this field. Storage of oxygen in liquid form is the optimal solution. Hydrogen can be stored in carbon-nanofibres or metallic hydrides, for example, or in liquid fuels, as alcohols, with further generation of the hydrogen required on-board. The objective of this study is to perform an exergetic analysis of two possibilities of using PEM fuel cells on surface ships and submarines: hydrogen/oxygen PEM fuel cells fed with hydrogen generated by reforming of methanol, and Direct Methanol Fuel Cells directly fed with liquid methanol. To do this, exergy losses and exergetic efficiencies are calculated for both configurations at selected optimal operation points.     

Performance assessment of a direct steam solar power plant with hydrogen energy storage: An exergoeconomic study

Power generation and its storage using solar energy and hydrogen energy systems is a promising approach to overcome serious challenges associated with fossil fuel-based power plants. In this study, an exergoeconomic model is developed to analyze a direct steam solar tower-hydrogen gas turbine power plant under different operating conditions. An on-grid solar power plant integrated with a hydrogen storage system composed of an electrolyser, hydrogen gas turbine and fuel cell is considered. When solar energy is not available, electrical power is generated by the gas turbine and the fuel cell utilizing the hydrogen produced by the electrolyser. The effects of different working parameters on the cycle performance during charging and discharging processes are investigated using thermodynamic analysis. The results indicate that increasing the solar irradiation by 36%, leads to 13% increase in the exergy efficiency of the cycle. Moreover, the mass flow rate of the heat transfer fluid in solar system has a considerable effect on the exergy cost of output power. Solar tower has the highest exergy destruction and capital investment cost. The highest exergoeconomic factor for the integrated cycle is 60.94%. The steam turbine and PEM electrolyser have the highest share of exergoeconomic factor i.e., 80.4% and 50%, respectively.     

Effects of leak current density and doping level on energetic,exergetic and ecological performance of a high-temperature PEM fuel cell

This paper presents a one-dimensional and semi-empirical model of a high-temperature PEM fuel cell (HT-PEMFC) to determine the performance characteristics through energy, exergy, and ecological analysis. The proposed model is compared with different experimental studies and supported by a few statistical approaches to prove its accuracy. As a result, the minimum and maximum R² values are determined to be 99.67% and 99.97%, respectively. In addition, the performance of the fuel cell is investigated under varying leakage current densities and doping levels. Accordingly, increasing the leak current density decreases the power density, net output voltage, energy efficiency, and exergy efficiency by 5.77%, 5.88%, 5.44%, and 5.48%, respectively, whereas increasing the doping level boosts these parameters by 23.07%, 11.76%, 30.25%, and 32.52%, respectively. In addition, increasing the leak density decreases all ecological functions. In contrast, raising the doping level increases the ecological parameters considerably and reduces the improvement potential.     

Thermodynamic modeling and exergy analysis of proton exchange membrane fuel cell power system

The proton exchange membrane (PEM) fuel cell (PEMFC) is equipped with a series of auxiliary components which consume considerable amount of energy. It is necessary to investigate the design and operation of the PEMFC power system for better system performance. In this study, a typical PEMFC power system is developed, and a thermodynamic model of the system is established. Simulation is carried out, and the power distribution of each auxiliary component in the system, the net power and power efficiency of the system are obtained. This power system uses cooling water for preheating inlet gases, and its energy-saving effect is also verified by the simulation. On this basis, the exergy analysis is applied on the system, and the indexes of the system exergy loss, exergy efficiency and ecological function are proposed to evaluate the system performance. The results show that fuel cell stack and heat exchanger are the two components that cause the most exergy loss. Furthermore, the system performance under various stack inlet temperatures and current densities is also analyzed. It is found that the net power, energy efficiency and exergy efficiency of the system reach the maximum when the stack inlet temperature is about 348.15 K. The ecological function is maintained at a high level when the stack inlet temperature is around 338.15 K. Lower current density increases the system ecological function and the power and exergy efficiencies, and also helps decrease the system exergy loss, but it decreases the system net power.     

Thermodynamic modeling of an integrated biomass gasification and solid oxide fuel cell system

An integrated process of biomass gasification and solid oxide fuel cells (SOFC) is investigated using energy and exergy analyses. The performance of the system is assessed by calculating several parameters such as electrical efficiency, combined heat and power efficiency, power to heat ratio, exergy destruction ratio, and exergy efficiency. A performance comparison of power systems for different gasification agents is given by thermodynamic analysis. Exergy analysis is applied to investigate exergy destruction in components in the power systems. When using oxygen-enriched air as gasification agent, the gasifier reactor causes the greatest exergy destruction. About 29% of the chemical energy of the biomass is converted into net electric power, while about 17% of it is used to for producing hot water for district heating purposes. The total exergy efficiency of combined heat and power is 29%. For the case in which steam as the gasification agent, the highest exergy destruction lies in the air preheater due to the great temperature difference between the hot and cold side. The net electrical efficiency is about 40%. The exergy combined heat and power efficiency is above 36%, which is higher than that when air or oxygen-enriched air as gasification agent.     

Metal bipolar plates for PEM fuel cell—A review

The polymer electrolyte membrane (PEM) based fuel cells are clean alternative energy systems that hold excellent potential for cost effectiveness, durability, and relatively high overall efficiency. PEM fuel cell is recognized by the U.S. Department of Energy (DOE) as the main candidate to replace the internal combustion engine in transportation applications. Metallic bipolar plates and membrane electrode assembly (MEA) are two crucial components of a PEM power stack and their durability and fabrication cost must be optimized to allow fuel cells to penetrate the commercial market and compete with other energy sources.     

Thermodynamic analysis of a Proton Exchange Membrane fuel cell

In this study, energy and exergy analyses of a 1 kW Horizon H-1000 XP Proton Exchange Membrane (PEM) Fuel Cell has been investigated. A testing apparatus has been established to analyze the system efficiencies based on the first and second laws of thermodynamics. In this mechanism pure hydrogen has been directly used as a fuel in compressed gas formation. Purity of hydrogen was above 99.99%. The system performance was investigated through experimental studies on energy and parametric studies on exergy by changing the operating pressure and operation temperature. The results showed that the energy efficiency of PEM fuel cell is 45.58% for experimental study and 41.27% for parametric study at full load. Also, 2.25% and 4.2% performance improvements were obtained by changing the operating temperature ratio (T/T₀) from 1 to 1.2 and operating pressure ratio (P/P₀) from 1 to 2, respectively.     

Decentralized generation of electricity from biomass with proton exchange membrane fuel cell

Biomass can be applied as the primary source for the production of hydrogen in the future. The biomass is converted in an atmospheric fluidized bed gasification process using steam as the gasifying agent. The producer gas needs further cleaning and processing before the hydrogen can be converted in a fuel cell; it is assumed that the gas cleaning processes are able to meet the requirements for a PEM-FC. The compressed hydrogen is supplied to a hydrogen grid and can be used in small-scale decentralized CHP units. In this study it is assumed that the CHP units are based on low temperature PEM fuel cells. For the evaluation of alternative technologies the whole chain of centralized hydrogen production from biomass up to and including decentralized electricity production in PEM fuel cells is considered.Two models for the production of hydrogen from biomass and three models for the combined production of electricity and heat with PEM fuel cells are built using the computer program Cycle-Tempo. Two different levels of hydrogen purity are considered in this evaluation: 60% and 99.99% pure hydrogen. The purity of the hydrogen affects both the efficiencies of the hydrogen production as well as the PEM-FC systems. The electrical exergy efficiency of the PEM-FC system without additional heat production is calculated to be 27.66% in the case of 60% hydrogen and 29.06% in the case of 99.99% pure hydrogen. The electrical exergy efficiencies of the whole conversion chain appear to be 21.68% and 18.74%, respectively. The high losses during purification of the hydrogen gas result in a higher efficiency for the case with low purity hydrogen. The removal of the last impurities strongly increases the overall exergy losses of the conversion chain.