Performance evaluation of high-efficiency SOFC-PEMFC hybrid system fueled by liquid ammonia

The liquid ammonia-fueled SOFC-PEMFC (solid oxide fuel cell-proton exchange membrane fuel cell) hybrid system is studied, and the influence of three factors on the energy efficiency of the system is analyzed. The results show that when the SOFC fuel utilization rate gradually increases, the maximum power of the hybrid system is 1277.85 kW, the total electrical efficiency of the system can reach 62.55%, the combined cooling and power (CCP) efficiency is the highest 69.25%, and the thermoelectric efficiency is gradually increased to 93.19%. When the SOFC operating temperature gradually increases, the electrical efficiency of the hybrid system is the highest 62.72%, the CCP efficiency is 69.41%, and the thermoelectric efficiency is basically maintained at about 90%. When the SOFC operating pressure gradually increases, the total power of the system is up to 1352.19 kW, the electrical efficiency and CCP efficiency of the system are about 60%, and the thermoelectric efficiency of the system is basically maintained between 88% and 95%.     

Optimization of a 30 kW SOFC combined heat and power system with different cycles and hydrocarbon fuels

Solid oxide fuel cells (SOFCs) could generate power cleanly and efficiently by using a wide range of fuels. Through the recovery and utilization of the energy in the SOFC tail gas, SOFC combined heat and power (CHP) systems achieve efficient cascade utilization of fuels. In this article, an efficient 30 kW SOFC CHP system with multiple cycles is designed based on a commercial kw-level SOFC device. The energy and substances could be recycled at multiple levels in this system, which makes the system do not need external water supply anymore during working. Meanwhile, the performance, fuel applicability, flexibility and reliability of the system are investigated. Finally, an optimized operating condition is confirmed, in which the electrical efficiency is 54.0%, and the thermoelectric efficiency could reach 88.8% by using methanol as fuel.     

Grid connected fuel cell and PV hybrid power generating system design with Matlab Simulink

Renewable energy sources have been taken the place of the traditional energy sources and especially rapidly developments of photovoltaic (PV) technology and fuel cell (FC) technology have been put forward these renewable energy sources (RES) in all other RES. PV systems have been started to be used widely in domestic applications connected to electrical grid and grid connected PV power generating systems have become widespread all around the world. On the other hand, fuel cell power generating systems have been used to support the PV generating so hybrid generation systems consist of PV and fuel cell technology are investigated for power generating. In this study, a grid connected fuel cell and PV hybrid power generating system was developed with Matlab Simulink. 160 Wp solar module was developed based on solar module temperature and solar irradiation by using real data sheet of a commercial PV module and then by using these modules 800 Wp PV generator was obtained. Output current and voltage of PV system was used for input of DC/DC boost converter and its output was used for the input of the inverter. PV system was connected to the grid and designed 5 kW solid oxide fuel cell (SOFC) system was used for supporting the DC bus of the hybrid power generating system. All results obtained from the simulated hybrid power system were explained in the paper. Proposed model was designed as modular so designing and simulating grid connected SOFC and PV systems can be developed easily thanks to flexible design.     

Comparison of three different control strategies for load-change and attenuation of solid oxide fuel cell system

Solid oxide fuel cell (SOFC) with a lot of advantages, such as high efficiency, low emission and great fuel compatibility, has broad application prospects in many fields. However, an appropriate control strategy is necessary for SOFC systems, which could not only maintain high system efficiency during load-change, but also supplement power after attenuation to extend system service life. In the article, three different control strategies are proposed, in which fuel flow, fuel utilization and cell voltage are controlled as constants respectively. The performance and applicability of strategies for load-change and cell degradation are evaluated through experiment data and simulations. Meanwhile, stack temperature, voltage, fuel utilization and efficiency are selected as main constraints to analyze the application scope of strategies. And in load increasing process of a 1 kW SOFC combined heat and power (CHP) system fed with methanol, the strategies are adopted to verify their effectiveness.     

Performance comparison of three solid oxide fuel cell power systems

An energy analysis of three typical solid oxide fuel cell (SOFC) power systems fed by methane is carried out with detailed thermodynamic model. Simple SOFC system, hybrid SOFC‐gas turbine (GT) power system, and SOFC‐GT‐steam turbine (ST) power system are compared. The influences of air ratio and operative pressure on the performance of SOFC power systems are investigated. The net system electric efficiency and cogeneration efficiency of these power systems are given by the calculation model. The results show that internal reforming SOFC power system can achieve an electrical efficiency of more than 49% and a system cogeneration efficiency including waste heat recovery of 77%. For SOFC‐GT system, the electrical efficiency and cogeneration efficiency are 61% and 80%, respectively. Although SOFC‐GT‐ST system is more complicated and has high investment costs, the electrical efficiency of it is close to that of SOFC‐GT system. Copyright © 2013 John Wiley & Sons, Ltd.     

Thermo-economic modeling of an indirectly coupled solid oxide fuel cell/gas turbine hybrid power plant

Power generation using gas turbine (GT) power plants operating on the Brayton cycle suffers from low efficiencies, resulting in poor fuel to power conversion. A solid oxide fuel cell (SOFC) is proposed for integration into a 10 MW gas turbine power plant, operating at 30% efficiency, in order to improve system efficiencies and economics. The SOFC system is indirectly coupled to the gas turbine power plant, paying careful attention to minimize the disruption to the GT operation. A thermo-economic model is developed for the hybrid power plant, and predicts an optimized power output of 20.6 MW at 49.9% efficiency. The model also predicts a break-even per-unit energy cost of USD 4.65 ¢ kWh⁻¹ for the hybrid system based on futuristic mass generation SOFC costs. This shows that SOFCs may be indirectly integrated into existing GT power systems to improve their thermodynamic and economic performance.     

Performance evaluation of different configurations of biogas-fuelled SOFC micro-CHP systems for residential applications

Three configurations of solid oxide fuel cell (SOFC) micro-combined heat and power (micro-CHP) systems are studied with a particular emphasis on the application for single-family detached dwellings. Biogas is considered to be the primary fuel for the systems studied. In each system, a different method is used for processing the biogas fuel to prevent carbon deposition over the anode of the cells used in the SOFC stack. The anode exit gas recirculation, steam reforming, and partial oxidation are the methods employed in systems I–III, respectively. The results predicted through computer simulation of these systems confirm that the net AC electrical efficiency of around 42.4%, 41.7% and 33.9% are attainable for systems I–III, respectively. Depending on the size, location and building type and design, all the systems studied are suitable to provide the domestic hot water and electric power demands for residential dwellings. The effect of the cell operating voltage at different fuel utilization ratios on the number of cells required for the SOFC stack to generate around 1 kW net AC electric power, the thermal-to-electric ratio (TER), the net AC electrical and CHP efficiencies, the biogas fuel consumption, and the excess air required for controlling the SOFC stack temperature is also studied through a detailed sensitivity analysis. The results point out that the cell design voltage is higher than the cell voltage at which the minimum number of cells is obtained for the SOFC stack.     

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.     

Simulation analysis of a system combining solid oxide and polymer electrolyte fuel cells

We evaluated the performance of system combining a solid oxide fuel cell (SOFC) stack and a polymer electrolyte fuel cell (PEFC) stack by a numerical simulation. We assume that tubular-type SOFCs are used in the SOFC stack. The electrical efficiency of the SOFC–PEFC system increases with increasing oxygen utilization rate in the SOFC stack. This is because the amount of exhaust heat of the SOFC stack used to raise the temperature of air supplied to it decreases as its oxygen utilization rate increases and because that used effectively as the reaction heat of the steam reforming reaction of methane in the stack reformer increases. The electrical efficiency of the SOFC–PEFC system at 190 kW ac is 59% (LHV), which is equal to that of the SOFC-gas turbine combined system at 1014 kW ac.     

U.S. DOE fossil energy fuel cells program

The U.S. Department of Energy's (DOE) Office of Fossil Energy's (FE) National Energy Technology Laboratory (NETL), in partnership with private industry, educational institutions and national laboratories, is leading the development and demonstration of high efficiency, high temperature solid oxide fuel cells (SOFCs) and fuel cell turbine (FCT) hybrid power generation systems for stationary markets including auxiliary power units (APUs), distributed generation (DG) and large, coal-based central power plants. The DOE FE fuel cells program has three aspects: the Solid State Energy Conversion Alliance (SECA), Fuel Cell Coal Based Systems for central power, and the High Temperature Electrochemistry Center (HiTEC). The SECA goal is to decrease SOFC system cost to US$ 400 per kilowatt (kW) by 2010 for stationary markets. DOE FE is ultimately concerned with coal-based central power plants such as FutureGen. The goal is to aggregate SECA-type fuel cells into larger systems and to produce a very high efficiency megawatt-class FCT hybrid for testing at FutureGen. The low-cost, US$ 400 kW⁻¹ SECA FCT hybrid is a key component to achieving 60% efficiency by 2020. Advanced aspects of solid oxide technology are part of HiTEC R&D. Technical progress and advances are discussed for all three program aspects.     

Synergistic integration of a gas turbine and solid oxide fuel cell for improved transient capability

A theoretical solid oxide fuel cell–gas turbine hybrid system has been designed using a Capstone 60 kW micro-gas turbine. Through simulation it is demonstrated that the hybrid system can be controlled to achieve transient capability greater than the Capstone 60 kW recuperated gas turbine alone. The Capstone 60 kW gas turbine transient capability is limited because in order to maintain combustor, turbine and heat exchangers temperatures within operating requirements, the Capstone combustor fuel-to-air ratio must be maintained. Potentially fast fuel flow rate changes, must be limited to the slower, inertia limited, turbo machinery air response. This limits a 60 kW recuperated gas turbine to transient response rates of approximately 1 kW s⁻¹. However, in the SOFC/GT hybrid system, the combustor temperature can be controlled, by manipulating the fuel cell current, to regulate the amount of fuel sent to the combustor. By using such control pairing, the fuel flow rate does not have to be constrained by the air flow in SOFC/GT hybrid systems. This makes it possible to use the rotational inertia of the gas turbine, to buffer the fuel cell power response, during fuel cell fuel flow transients that otherwise limit fuel cell system transient capability. Such synergistic integration improves the transient response capability of the integrated SOFC gas turbine hybrid system. Through simulation it has been demonstrated that SOFC/GT hybrid system can be developed to have excellent transient capability.     

Thermo-economic modeling of a solid oxide fuel cell/gas turbine power plant with semi-direct coupling and anode recycling

Power generation using gas turbine (GT) power plants operating on the Brayton cycle suffers from low efficiencies, resulting in poor fuel to power conversion. A solid oxide fuel cell (SOFC) is proposed for integration into a 10 MW gas turbine power plant, operating at 30% efficiency in order to improve system efficiencies and economics. The SOFC system is semi-directly coupled to the gas turbine power plant, with careful attention paid to minimize the disruption to the GT operation. A thermo-economic model is developed for the hybrid power plant, and predicts an optimized power output of 21.6 MW at 49.2% efficiency. The model also predicts a breakeven per-unit energy cost of USD 4.70 ¢/kWh for the hybrid system based on futuristic mass generation SOFC costs. Results show that SOFCs can be semi-directly integrated into existing GT power systems to improve their thermodynamic and economic performance.     

Thermodynamic analysis of ITSOFC hybrid system for polygenerations

Solid oxide fuel cell (SOFC) is an energy conversion device that produces electricity directly from fossil fuels through electrochemical reactions. Intermediate and low temperature SOFCs (IT/LT, 300–800 °C SOFCs) are the main strains of the world SOFC R&D now. The exhaust gas of SOFC has high value in use. So SOFC is often integrated into a hybrid system with other power systems. Research shows that the electrical efficiency and the total efficiency of a hybrid system can be about 60% and 80% higher than an independent one. In this paper, the performance of intermediate temperature SOFC hybrid system was analyzed. Based on presenting a steady-state mathematical model of ITSOFC, the steady-state model of each designed system was presented. Results show that a hybrid system can achieve high efficiency. The results of this research can be useful in design and application for polygenerations integrated by SOFCs.     

Parameter optimization study on SOFC‐MGT hybrid power system

This paper mainly studied the solid oxide fuel cell (SOFC)–micro gas turbine (MGT) hybrid power system. The key parameters that greatly influence the overall system performance have been studied and optimized. The thermodynamic potential of improving the hybrid system performance by integrating SOFC with the advanced thermal cycle system is analyzed. The optimization rules of main parameters of SOFC‐MGT hybrid power system with the turbine inlet temperature (TIT) of MGT as a constraint condition are revealed. The research results show that TIT is a key parameter that limits the electrical efficiency of hybrid power system. With the increase of the cell number, both the power generation efficiency of the hybrid cycle power system and TIT increase. Regarding the hybrid system with the fixed cell number, in order to get a higher electrical efficiency, the operating temperature of SOFC should be enhanced as far as possible. However, the higher operating temperature will result in the higher TIT. Increasing of fuel utilization factor is an effective measure to improve the performance of hybrid system. At the same time, TIT increases slightly. Both the electrical efficiency of hybrid power system and TIT reduce with the increase of the ratio of steam to carbon. The achievements obtained from this paper will provide valuable information for further study on SOFC‐MGT hybrid power system with high efficiency. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of methane processing strategy on fuel composition,electrical and thermal efficiency of solid oxide fuel cell

Natural gas is a cheap and abundant fuel for solid oxide fuel cell (SOFC), generally integrating the SOFC system with methane pre-treating system for improving the stability of SOFC. In this paper, the accurate effects of methane processing strategy on fuel composition, electrical efficiency and thermal efficiency of SOFC are investigated based on the thermodynamic equilibrium. Steam reforming of methane is an endothermic process and can produce 3 mol of H₂ and 1 mol of CO from 1 mol of methane, and thus the electrical efficiency of SOFC is high at the same O/C ratio and equivalent fuel utilization, whereas the thermal efficiency is low. On the contrary, partial oxidation of methane is an exothermal process and only produces 2 mol of H₂ and 1 mol of CO from 1 mol of methane, and thus the electrical efficiency of SOFC is low at the same O/C ratio and equivalent fuel utilization, whereas the thermal efficiency is high. When the O/C ratio is 1.5, the electrical efficiency of SOFC is 55.3% for steam reforming of methane, while 32.7% for partial oxidation of methane. High electrical efficiency of SOFC can be achieved and carbon deposition can be depressed by selecting suitable O/C ratio from methane pretreatment according to the accurate calculation and analysis of effects of different methane processing strategies on the electrical efficiency and thermal efficiency of SOFC.     

Liquid fuel utilization in SOFC hybrid systems

The interest in solid oxide fuel cell systems comes from their capability of converting the chemical energy of traditional fuels into electricity, with high efficiency and low pollutant emissions. In this paper, a study of the design space of solid oxide fuel cell and gas turbine hybrids fed by methanol and kerosene is presented for stationary power generation in isolated areas (or transportation). A 500 kW class hybrid system was analysed using WTEMP original software developed by the Thermochemical Power Group of the University of Genoa. The choice of fuel-processing strategy and the influence of the main design parameters on the thermoeconomic characteristics of hybrid systems were investigated. The low capital and fuel cost of methanol systems make them the most attractive solutions among those investigated here.     

Introducing an integrated SOFC,linear Fresnel solar field,Stirling engine and steam turbine combined cooling,heating and power process

A new integrated combined cooling, heating and power system which includes a solid oxide fuel cell, Stirling engine, steam turbine, linear Fresnel solar field and double effect absorption chiller is introduced and investigated from energy, exergy and thermodynamic viewpoints. In this process, produced electrical power by the fuel cell and steam turbines is 6971.8 kW. Stirling engine uses fuel cell waste heat and produces 656 kW power. In addition, absorption chiller is driven by waste heat of the Stirling engine and generates 2118.8 kW of cooling load. Linear Fresnel solar field produces 961.7 kW of thermal power as a heat exchanger. The results indicate that, electrical, energy and exergy efficiencies and total exergy destruction of the proposed system are 49.7%, 67.5%, 55.6% and 12560 kW, respectively. Finally, sensitivity analysis to investigate effect of the different parameters such as flow rate of inputs, outlet pressure of the components and temperature changes of the solar system on the hybrid system performance is also done.     

Solid oxide fuel cell-lithium battery hybrid power generation system energy management: A review

The solid oxide fuel cell (SOFC)/lithium battery hybrid energy structure uses lithium batteries as the energy buffer unit to ensure that the SOFC can operate safely and stably when the load power increases suddenly. For the SOFC/lithium battery hybrid power generation system, a real-time energy management strategy based on power prediction is discussed, and an in-depth summary is made from system construction, power prediction, energy distribution, and power tracking. In the hybrid power generation system, the SOFC system and the lithium battery influence each other. Research the appropriate energy management strategies and realize real-time energy distribution and tracking of hybrid power generation systems in order to improve system performance and economy. This has become a key issue in the current SOFC hybrid power generation system research field.     

Thermo-economic optimization of an indirectly coupled solid oxide fuel cell/gas turbine hybrid power plant

Power generation using gas turbine (GT) power plants operating on the Brayton cycle suffers from low efficiencies, resulting in poor fuel to power conversion. A solid oxide fuel cell (SOFC) is proposed for integration into a 10-MW GT power plant, operating at 30% efficiency, in order to improve system efficiencies and economics. The SOFC system is indirectly coupled to the GT, in order to minimize the disruption to the GT operation. A thermo-economic model is developed to simulate the hybrid power plant and to optimize its performance using the method of Lagrange Multipliers. It predicts an optimized power output of 18.9 MW at 48.5% efficiency, and a breakeven per-unit energy cost of USD 4.54 ¢ kW h⁻¹ for the hybrid system based on futuristic mass generation SOFC costs.     

Fast and stable operation approach of ship solid oxide fuel cell-gas turbine hybrid system under uncertain factors

This work focuses on investigating the adaptability of solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system for ship application under uncertain factors. The effect of rapids, wind and waves on the performance of ship SOFC-GT is analyzed. In addition, a novel control system combining fuzzy logic theory, temperature feedforward and coordination factor on-line adjustment is proposed to address the problem of load disturbances caused by uncertain factors. The results show that the proposed operation strategy can shorten the thermal response time inside fuel cell stacks by almost 49.97%, meanwhile, reducing the maximum temperature changing rate at the electrochemically active tri-layer cell composed of anode, electrolyte, and cathode (PEN structure) by around 17.86%. Moreover, the reasonable matching between air flow and fuel flow is an essential prerequisite to ensure the safe and efficient operation of ship SOFC-GT. While the SOFC-GT is working at full load, the results indicate that the fuel to air ratio cannot exceed 2.56?10^?2 g/g. Finally, an application scenario of the 5000-ton river-to-sea cargo ship sails from Nanjing Port to Yangshan Port (Eastern China) is conducted to analyze the operation characteristics of ship SOFC-GT under uncertain factors. Two set of 1000 kW SOFC-GT systems with the electrical efficiency of 64.66% is designed for the target ship, the results conclude that the operation strategy of each SOFC-GT system supports 50% load is beneficial in reducing the power tracking time and SOFC temperature overshoot. The average electrical efficiency of 61.45% and 61.04% are achieved in winter and summer typical days respectively in the whole voyage.