Thermodynamic assessment of photovoltaic systems

In this paper, an attempt is made to investigate the performance characteristics of a photovoltaic (PV) and photovoltaic-thermal (PV/T) system based on energy and exergy efficiencies, respectively. The PV system converts solar energy into DC electrical energy where as, the PV/T system also utilizes the thermal energy of the solar radiation along with electrical energy generation. Exergy efficiency for PV and PV/T systems is developed that is useful in studying the PV and PV/T performance and possible improvements. Exergy analysis is applied to a PV system and its components, in order to evaluate the exergy flow, losses and various efficiencies namely energy, exergy and power conversion efficiency. Energy efficiency of the system is calculated based on the first law of thermodynamics and the exergy efficiency, which incorporates the second law of thermodynamics and solar irradiation exergy values, is also calculated and found that the latter is lower for the electricity generation using the considered PV system. The values of “fill factor” are also determined for the system and the effect of the fill factor on the efficiencies is also evaluated. The experimental data for a typical day of March (27th March 2006) for New Delhi are used for the calculation of the energy and exergy efficiencies of the PV and PV/T systems. It is found that the energy efficiency varies from a minimum of 33% to a maximum of 45% respectively, the corresponding exergy efficiency (PV/T) varies from a minimum of 11.3% to a maximum of 16% and exergy efficiency (PV) varies from a minimum of 7.8% to a maximum of 13.8%, respectively.     

Energy and exergy analyses of a combined ammonia-fed solid oxide fuel cell system for vehicular applications

In this study, both energetic and exergetic performances of a combined heat and power (CHP) system for vehicular applications are evaluated. This system proposes ammonia-fed solid oxide fuel cells based on proton conducting electrolyte (SOFC-H⁺) with a heat recovery option. Fuel consumption of combined fuel cell and energy storage system is investigated for several cases. The performance of the portable SOFC system is studied in a wide range of the cell’s average current densities and fuel utilization ratios. Considering a heat recovery option, the system exergy efficiency is calculated to be 60-90% as a function of current density, whereas energy efficiency varies between 60 and 40%, respectively. The largest exergy destructions take place in the SOFC stack, micro-turbine, and first heat exchanger. The entropy generation rate in the CHP system shows a 25% decrease for every 100 °C increase in average operating temperature.     

Understanding energy and exergy efficiencies for improved energy management in power plants

An extensive overview is provided of various energy- and exergy-based efficiencies used in the analysis of power cycles. Vapor and gas power cycles, cogeneration cycles and geothermal power cycles are examined, and consideration is given to different cycle designs. The many approaches that can be used to define efficiencies are provided and their implications discussed. Improvements of the management of energy in power plants that stem from understanding the efficiencies better are described. Examples are given to illustrate the efficiencies and their differences, with the results presented using combined energy and exergy diagrams. It is anticipated that the results will provide a convenient and practical tool for engineers and researchers dealing with the analysis, design, optimization and improvement of power cycles.     

Energy and exergy analyses of a hybrid molten carbonate fuel cell system

This study deals with the energy and exergy analysis of a molten carbonate fuel cell hybrid system to determine the efficiencies, irreversibilities and performance of the system. The analysis includes the operation of each component of the system by mass, energy and exergy balance equations. A parametric study is performed to examine the effect of varying operating pressure, temperature and current density on the performance of the system. Furthermore, thermodynamic irreversibilities in each component of the system are determined. An overall energy efficiency of 57.4%, exergy efficiency of 56.2%, bottoming cycle energy efficiency of 24.7% and stack energy efficiency of 43.4% are achieved. The results demonstrate that increasing the stack pressure decreases the overpotential losses and, therefore, increases the stack efficiency. However, this increase is limited by the remaining operating conditions and the material selection of the stack. The fuel cell and the other components in which chemical reactions occur, show the highest exergy destruction in this system. The compressor and turbine on the other hand, have the lowest entropy generation and, thus, the lowest exergy destruction.     

On-line fuzzy energy management for hybrid fuel cell systems

Fuel Cell Hybrid Vehicles (FCHV) can reach near zero emission by removing the conventional internal combustion from the vehicle powertrain. Nevertheless, before seeing competitive and efficient FCHV on the market, at market prices, different technical, economic, and social challenges should be overcome. A typical hybrid fuel cell powertrain combines a fuel cell stack and a dedicated energy storage system along with their necessary power converters. Energy storage systems are used in order to enhance the well-to-wheel efficiency and thus reducing the hydrogen consumption. An efficient management of power flows on the vehicle, allows optimizing the recovery of energy braking. Moreover, working in the fuel cell maximum efficiency leads to reduced thermal losses and thus to the downsizing of the heat exchangers. This paper presents an enhanced control of the power flows on a FCHV in order to reduce the hydrogen consumption, by generating and storing the electrical energy only at the most suitable moments on a given driving cycle. While the off-line optimization-based on dynamic programming algorithm offers the necessary optimal comparison reference on a known demand, the proposed strategy which can be implemented on-line, is based on a fuzzy logic decision system. The fine tuning of the fuzzy system parameters (mainly the membership functions and the gains), is made using a genetic algorithm and the fuzzy supervisor shows performing results for different load profiles.     

Effect of gasification agent on the performance of solid oxide fuel cell and biomass gasification systems

In this paper, an integrated solid oxide fuel cell (SOFC) and biomass gasification system is modeled to study the effect of gasification agent (air, enriched oxygen and steam) on its performance. In the present modeling, a heat transfer model for SOFC and thermodynamic models for the rest of the components are used. In addition, exergy balances are written for the system components. The results show that using steam as the gasification agent yields the highest electrical efficiency (41.8%), power-to-heat ratio (4.649), and exergetic efficiency (39.1%), but the lowest fuel utilization efficiency (50.8%). In addition, the exergy destruction is found to be the highest at the gasifier for the air and enriched oxygen gasification cases and the heat exchanger that supplies heat to the air entering the SOFC for the steam gasification case.     

Development,analysis and assessment of fuel cell and photovoltaic powered vehicles

This paper deals with a new hybridly powered photovoltaic- PEM fuel cell – Li-ion battery and ammonia electrolyte cell integrated system (system 2) for vehicle application and is compared to another system (system 1) that is consisting of a PEM fuel cell, photovoltaic and Li-ion battery. The paper aims to investigate the effect of adding photovoltaic to both systems and the amount of hydrogen consumption/production that could be saved/generated if it is implemented in both systems. These two systems are analyzed and assessed both energetically and exergetically. Utilizing photovoltaic arrays in system 1 is able to recover 177.78 g of hydrogen through 1 h of continuous driving at vehicle output power of 98.32 kW, which is approximately 3.55% of the hydrogen storage tank used in the proposed systems. While, using the same photovoltaics arrays, system 2 succeeds to produce 313.86 g of hydrogen utilizing the ammonia electrolyzer system 2 appeared to be more promising as it works even if the car is not in operation mode. Moreover, the hydrogen produced from the ammonia electrolyzer can be stored onboard, and the liquefied ammonia can be used as a potential source for feeding PEM fuel cell with hydrogen. Furthermore, the effects of changing various system parameters on energy and exergy efficiencies of the overall system are investigated.     

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.     

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.     

A review: Exergy analysis of PEM and PEM fuel cell based CHP systems

In recent years, growing attention has been given to new alternative energy sources and exergy analysis since fossil fuels cause emissions that have some negative impacts on earth such as global warming, greenhouse effect etc. New power generation systems have been developed in order to reduce or eliminate these impacts as possible. So that, new alternative energy systems have been taken place instead of fossil fuel based systems with nearly zero emission levels. One of them is solid polymer electrolyte or proton exchange membrane (PEM) fuel cell. Although it has significant advantages, there are some disadvantages such as cost, and hydrogen is not a fuel that can be easily obtained. For these reasons, efficiency of a PEM fuel cell has a great significance. Energy efficiency of a system is the most important parameter for utilization. But, energy analysis does not always show the capacity to do work potential of energy of a system. Exergy analysis must be investigated for a system in order to see available work of the system. Because of disadvantages of the PEM fuel cell, exergy analysis has quite importance. In this paper PEM fuel cell and exergy analysis of PEM fuel cell are combined and investigated. A detailed review of the past and recent research activities has been documented. The review focuses on exergy analysis of both PEM fuel cells and PEM based combined heat and power (CHP) systems at different operating parameters. It is concluded that there are a lot of parameters which effects the exergy efficiencies of systems.     

Comparative assessments of two integrated systems with/without fuel cells utilizing liquefied ammonia as a fuel for vehicular applications

In the current study, two different integrated systems for vehicular applications are presented and thermodynamically analyzed. The first system consists of liquefied ammonia tank, dissociation and separation unit (DSC) for decomposition of ammonia and an internal combustion engine (ICE) to power the vehicle. The second system is a hybrid system consisting of liquefied ammonia tank, DSC unit, a small ICE and a fuel cell system. In the second system, the main power unit is fuel cell and a supplementary internal combustion engines is also utilized. The exhaust gasses emitted from the ICE are used to provide the required heat for the thermal decomposition process of ammonia. The ICE is fueled with a mix of ammonia and hydrogen generated from the DSC unit that is installed in the two systems. Hydrogen generated from DSC unit will be utilized to operate fuel cell installed in system 2. The proposed systems are analyzed and assessed both energetically and exergetically. A comprehensive parametric study is carried out for comparative assessments to determine the influence of altering design and operating parameters such as the amount of ammonia fuel supplied to the two systems on the performance of the two systems. The overall energy and exergy efficiencies for system 1 and system 2 are found to be 61.89%, 63.34%, 34.73% and 38.44% respectively. The maximum exergy destruction rate in the two systems occurred in the ICE.     

A new hybrid solar photovoltaic/ phosphoric acid fuel cell and energy storage system; Energy and Exergy performance

Present work investigates the performance of a combined solar photovoltaic (PV) and Pumped-Hydro and Compressed-Air energy storage system to overcome the challenges of using solar energy systems. This energy system, which is one of the newest hybrid systems, is able to generate electricity and store energy. To examine the solar PV performance the climatic conditions of Shiraz (in Iran) and Abu Dhabi (in UAE) are considered. The results revealed that, the required pump work, which must be supplied by PV system, is equal to 2.85 and 2.62 MJ/m³ for isothermal and isentropic processes, respectively. Furthermore, the total system efficiency is equal to 76.5%. In addition, the total exergy destruction of hybrid system for isentropic process is 8.91% less than that isothermal process. In addition, instead of the solar PV system, a phosphoric acid fuel cell is coupled to the storage system and the results are compared with the main system.     

Exergoeconomic analysis of a hybrid copper-chlorine cycle driven by geothermal energy for hydrogen production

In this study, we conduct an exergy, cost, energy and mass (EXCEM) analysis of a copper-chlorine thermochemical water splitting cycle driven by geothermal energy for hydrogen production. We also investigate and illustrate the relations between thermodynamic losses and capital costs. The results show that hydrogen cost is closely and directly related to the plant capacity and also exergy efficiency. Increasing economic viability and reducing the hydrogen production costs will help these cycles play a more critical role in switching to hydrogen economy.     

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.     

A review on photovoltaic/thermal hybrid solar technology

A significant amount of research and development work on the photovoltaic/thermal (PVT) technology has been done since the 1970s. Many innovative systems and products have been put forward and their quality evaluated by academics and professionals. A range of theoretical models has been introduced and their appropriateness validated by experimental data. Important design parameters are identified. Collaborations have been underway amongst institutions or countries, helping to sort out the suitable products and systems with the best marketing potential. This article gives a review of the trend of development of the technology, in particular the advancements in recent years and the future work required.     

Experimental results for hybrid energy storage systems coupled to photovoltaic generation in residential applications

An experimental solar-hydrogen powered residence simulator was built and tested. The system consisted of a solar photovoltaic array connected to an electrolyzer which produced hydrogen as a means of energy storage. The hydrogen was used to produce electricity in a fuel cell that operated in parallel with a battery to meet dynamic power demand similar to that found in residential applications. The study demonstrated the technical feasibility of operating such a system under the simultaneous dynamics of solar input and load. Limitations of current fuel cell and electrolyzer designs, as they pertain to both power delivery and energy storage, were identified. The study also established the need to understand and address dynamic performance in the design and application of solar-hydrogen reversible fuel cell hybrid systems. An economic analysis found that major cost reductions would need to be achieved for such systems to compete with conventional energy storage devices.     

Novel energy management method for suppressing fuel cell degradation in hydrogen and electric hybrid energy storage systems compensating renewable energy fluctuations

This research investigates an energy management method utilized in a hydrogen and electric hybrid energy storage system (HESS), which is utilized as an ancillary system for renewable energy electricity generation. To suppress the performance degradation of the fuel cell (FC), the newly proposed energy management method deals with main FC degradation causes, such as low humidification and frequent and rapid voltage changes. The entire HESS's performance is demonstrated using the proposed energy management method. In addition, a simulation is conducted to evaluate the proposed energy management method's performance in terms of both suppressing the FC's degradation and ensuring system efficiency. The results of the experiment and simulation show that the proposed energy management method can suppress the FC's harmful working states while maintaining high system efficiency.     

Energy and exergy analyses of a combined molten carbonate fuel cell - Gas turbine system

This study deals with the thermodynamic analysis of molten carbonate fuel cell combined with a gas turbine, based on the first- and second-law of thermodynamics. The mass, energy, entropy and exergy balance equations are written and applied to the system and its components. Some parametric studies are performed to investigate the change of system performance through energy and exergy efficiencies with the change of operating conditions. The irreversibilities occuring in different devices of the integrated system are also investigated through the exergy destruction analysis in these devices. The maximum output work of the MCFC is estimated to be 314.3 kW for an operating temperature of 650 °C. The overall energy and exergy efficiencies achieved for this system are 42.89% and 37.75%, respectively.     

Monitoring of energy exergy efficiencies and exergoeconomic parameters of geothermal district heating systems (GDHSs)

In this work, the monitoring energy and exergy efficiency results of the last heating seasons of operation of the geothermal district heating systems (GDHSs) and their technical availability analysis and monitoring exergoeconomic parameters are presented. The case studies cover the actual system data taken from the systems in Afyon and Salihli GDHSs, Turkey. General energy, exergy, technical availability, and exergoeconomic analysis of the GDHSs are introduced. Furthermore, the average technical availability, real availability, capacity factor and energy and exergy efficiencies value of GDHSs have been analyzed.     

A preliminary solar-hydrogen system for Jordan: Impacts assessment and scenarios analysis

Energy sector in Jordan faces serious challenges today. Jordan as a non-oil country depends by 96% on imported fuel to cover its demands. The present work seeks to improve an alternative fuel that can support the goals of National Energy Strategy in Jordan. Therefore; a mathematical model was developed to investigate the possibility of producing solar-hydrogen fuel in Jordan. Ma'an city was chosen to be the location of solar-hydrogen plant. The high solar insulation and the availability to supply the plant with water from Aqaba Gulf directly and/or from Red-Sea Dead-Sea Cannel make Ma'an the suitable location for the plant. A system with photovoltaic (PV) cell array and proton electron membrane (PEM) electrolyzer was suggested to be the connection system for the plant. Accordingly, two different scenarios were proposed for hydrogen production with different hydrogen production doubling time, the first scenario is ${\mathit{\theta }}_{\mathit{h}1}=2+0.15\left(\mathit{n}?1\right)$ year, while the second scenario is ${\mathit{\theta }}_{\mathit{h}2}=4+0.15(\mathit{n}?1)$ year. Eight different economic, social, and environmental parameters, which directly affect solar-hydrogen production, were evaluated and investigated for Jordan up to year 2060. Accordingly, the research study concluded that solar-hydrogen fuel can potentially offer a good option as an alternative fuel for Jordan. Starting the production at year of 2020 can provide a good sharing in energy demand sector by the end of the year 2060.