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Application of Solar Energy and Reversible Solid Oxide Fuel Cell in a Co-Generation System
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The sustainable energy sources have been concentrated over the last few decades. The solar energy and solid oxide fuel (SOFC) technology will be the promising possibility to tackle the energy poverty and environment pollution. Hence, the solar energy coupling with fuel cell technology can be a green energy solution for the next generation. In this study, a co-generation system is presented using the solar energy and reversible solid oxide fuel cell (RSOFC). The solar energy is used for power supply and steam electrolysis and the solid oxide fuel cell is used for hydrogen production from steam electrolysis as well as electricity and heat from generated hydrogen fuel (H2).
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... where, T is the cell temperature, P H 2 and P O 2 are hydrogen and oxygen flow pressures, R is the gas constant, and F is Faraday's constant [9]. E 0 is reference or ideal voltage taken as 1.229 in this paper. ...
... At higher current densities, the cell potential decreases rapidly due to mass limitations [9]. This linearity is termed as the concentration over potential which is shown in Eq. (5) as ...
In this paper, the mathematical analysis of electrochemical model of Solid Oxide Fuel Cell (SOFC) system has been done for MATLAB/Simulink modeling. Furthermore, the possible mechanism of the parameter influences effects and their interrelationships are discussed comprehensively. To investigate the performance of SOFC, the V and I characteristics, power density, current density, etc., analyzed by the influence effect of the important parameters. For this investigation , various important parameters, e.g., reactants' flow pressure, operating temperature, membrane resistance, etc., are considered. This study is very helpful to predict the performance of the SOFC.
Solid oxide fuel cells (SOFCs) have been considered as one of the most promising technologies for very high-efficiency electric energy generation from natural gas, both with simple fuel cell plants and with integrated gas turbine/steam turbine-fuel cell systems. The high temperature exhaust gas from SOFC can be utilized in other cycles i.e. Rankine, Brayton for additional power generation or for heating and cooling purpose (cogeneration/trigeneration). The analysis shows that the resulting maximum efficiency of this SOFC-combined system can be up to 90% depending upon the operating condition and configuration used. This paper reviews the application of SOFC technology in power generation sector. This paper also investigate the research work undertaken or going on in this field.
Due to the increasing future energy demands and global warming, the renewable alternative energy sources and the efficient power systems have been getting importance over the last few decades. Among the renewable energy technologies, the solar energy coupling with fuel cell technology will be the promising possibilities for the future green energy solutions. Fuel cell cogeneration is an auspicious technology that can potentially reduce the energy consumption and environmental impact associated with serving building electrical and thermal demands. In this study, performance assessment of a co-generation system is presented to deliver electrical and thermal energy using the solar energy and the reversible solid oxide fuel cell. A mathematical model of the co-generation system is developed. To illustrate the performance, the system is considered in three operation modes: a solar-solid oxide fuel cell (SOFC) mode, which is low solar radiation time when the solar photovoltaic (PV) and SOFC are used for electric and heat load supply; a solar-solid oxide steam electrolyzer (SOSE) mode, which is high solar radiation time when PV is used for power supply to the electrical load and to the steam electrolyzer to generate hydrogen (H2); and a SOFC mode, which is the power and heat generation mode of reversible SOFC using the storage H2 at night time. Also the effects of solar radiation on the system performances and the effects of temperature on RSOFC are analyzed. In this study, 100 kW electric loads are considered and analyzed for the power and heat generation in those three modes to evaluate the performances of the system. This study is also revealed the combined heat and power (CHP) efficiency of the system. The overall system efficiency achieved for the solar-SOFC mode is 23%, for the solar-SOSE mode is 20% and for the SOFC mode is 83.6%. Besides, the only electricity generation efficiency for the solar-SOFC mode is 15%, for the solar-SOSE mode is 14% and for the SOFC mode is 44.28%. An economic analysis is presented based on the annual electricity generation from the system and the system has shown the good economic viability in this study with a unit cost of energy (COE) about 0.068 $/kW h.
An experimental investigation on the performance and durability of single solid oxide cells (SOCs) is under way at the Idaho National Laboratory. Reversible operation of SOCs includes electricity generation in the fuel cell mode and hydrogen generation in the electrolysis mode. Degradation is a more significant issue when operating SOCs in the electrolysis mode. In order to understand and mitigate the degradation issues in high temperature electrolysis, single SOCs with different configurations from several manufacturers have been evaluated for initial performance and long-term durability. Cells were obtained from four industrial partners. Cells from Ceramatec Inc. and Materials and Systems Research Inc. (MSRI) showed improved durability in electrolysis mode compared to previous stack tests. Cells from Saint Gobain Advanced Materials Inc. (St. Gobain) and SOFCPower Inc. demonstrated stable performance in the fuel cell mode, but rapid degradation in the electrolysis mode, especially at high current density. Electrolyte–electrode delamination was found to have a significant impact on degradation in some cases. Enhanced bonding between electrolyte and electrode and modification of the electrode microstructure helped to mitigate degradation. Polarization scans and AC impedance measurements were performed during the tests to characterize cell performance and degradation.
A two-cell planar stack in the Jülich F-design with solid oxide cells has been built and the reversible operation between fuel cell and electrolysis modes has been demonstrated. The cells were anode supported cells (ASC) with yttria-stabilized zirconia (YSZ) electrolytes, Ni/YSZ hydrogen electrodes and perovskite oxygen electrodes with lanthanum strontium cobalt ferrite (LSCF). This paper summarizes and discusses the preliminary experimental results on the long-term aging tests of the reversible solid oxide planar short stack for fuel cell operation (4000 h) at a current density of 0.5 A cm−2 which shows a degradation of 0.6% per 1000 h and for steam electrolysis operation (3450 h) and co-electrolysis operation of CO2 and H2O (640 h) under different current densities from −0.3 to −0.875 A cm−2 which show different degradation rates depending on current density and on steam or co-electrolysis.
BaZr1−xCoxO3−δ (BZC-x, x = 0.1, 0.2, 0.3, 0.4, 0.5) are prepared and identified as single phase air electrode materials for reversible solid oxide cells. BZC-x shows a typical perovskite structure with x ≤ 0.4, and slight BaCoO3 second phase is observed with x = 0.5. Conductivity measurements suggest that BZC-x is an oxygen ion and electron mixed conductor in dry oxygen atmosphere. The electronic conductivity of BZC-x increases when increasing Co content in BZC-x specimen, while the ionic conductivity reduces. For BaZr0.6Co0.4O3−δ, the electronic and ionic conductivity are 5.24 S cm−1 and 1.20 × 10−3 S cm−1, respectively, measured at 700 °C in dry oxygen. With BZC-0.4 as a single phase air electrode, the discharging and electrolysis current densities of a single cell are 299 mA cm−2 (at 0.7 V) and −935 mA cm−2 (at 1.5 V), respectively, measured at 700 °C. The polarization resistance of cells using this new air electrode is only 0.19 Ω cm2, approximately 65% lower than that using a traditional Sm0.5Sr0.5CoO3−δ/BaCe0.5Zr0.3Y0.2O3−δ composite air electrode.
Energy and exergy analysis has been conducted to investigate the thermodynamic–electrochemical characteristics of hydrogen production by a solid oxide steam electrolyzer (SOSE) plant. All overpotentials involved in the SOSE cell have been included in the thermodynamic model. The waste heat in the gas stream of the SOSE outlet is recovered to preheat the H2O stream by a heat exchanger. The heat production by the SOSE cell due to irreversible losses has been investigated and compared with the SOSE cell's thermal energy demand. It is found that the SOSE cell normally operates in an endothermic mode at a high temperature while it is more likely to operate in an exothermic mode at a low temperature as the heat production due to overpotentials exceeds the thermal energy demand. A diagram of energy and exergy flows in the SOSE plant helps to identify the sources and quantify the energy and exergy losses. The exergy analysis reveals that the SOSE cell is the major source of exergy destruction. The energy analysis shows that the energy loss is mainly caused by inefficiency of the heat exchangers. The effects of some important operating parameters, such as temperature, current density, and H2O flow rate, on the plant efficiency have been studied. Optimization of these parameters can achieve maximum energy and exergy efficiencies. The findings show that the difference between energy efficiency and exergy efficiency is small as the high-temperature thermal energy input is only a small fraction of the total energy input. In addition, the high-temperature waste heat is of high quality and can be recovered. In contrast, for a low-temperature electrolysis plant, the difference between the energy and exergy efficiencies is more apparent because considerable amount of low-temperature waste heat contains little exergy and cannot be recovered effectively. This study provides a better understanding of the energy and exergy flows in SOSE hydrogen production and demonstrates the importance of exergy analysis for identifying and quantifying the exergy destruction. The findings of the present study can further be applied to perform process optimization to maximize the cost-effectiveness of SOSE hydrogen production.
Reversible solid oxide fuel cells (R-SOFCs) are regarded as a promising solution to the discontinuity in electric energy, since they can generate electric powder as solid oxide fuel cells (SOFCs) at the time of electricity shortage, and store the electrical power as solid oxide electrolysis cells (SOECs) at the time of electricity over-plus. In this work, R-SOFCs with thin proton conducting electrolyte films of BaCe0.5Zr0.3Y0.2O3−δ were fabricated and their electro-performance was characterized with various reacting atmospheres. At 700°C, the charging current (in SOFC mode) is 251mAcm−2 at 0.7V, and the electrolysis current densities (in SOEC mode) reaches −830mAcm−2 at 1.5V with 50% H2O–air and H2 as reacting gases, respectively. Their electrode performance was investigated by impedance spectra in discharging mode (SOFC mode), electrolysis mode (SOEC mode) and open circuit mode (OCV mode). The results show that impedance spectra have different shapes in all the three modes, implying different rate-limiting steps. In SOFC mode, the high frequency resistance (RH) is 0.07Ωcm2 and low frequency resistances (RL) are 0.37Ωcm2. While in SOEC mode, RH is 0.15Ωcm2, twice of that in SOFC mode, and RL is only 0.07Ωcm2, about 19% of that in SOFC mode. Moreover, the spectra under OCV conditions seems like a combination of those in SOEC mode and SOFC mode, since that RH in OCV mode is about 0.13Ωcm2, close to RH in SOEC mode, while RL in OCV mode is 0.39Ωcm2, close to RL in SOFC mode. The elementary steps for SOEC with proton conducting electrolyte were proposed to account for this phenomenon.