A dynamic model of a 100 MW solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system has been developed and subjected to perturbations in diurnal ambient temperature and pressure as well as load sheds. The dynamic system responses monitored were the fuel cell electrolyte temperature, gas turbine shaft speed, turbine inlet temperature and compressor surge. Using a control strategy that primarily focuses on holding fuel cell electrolyte temperature constant and secondarily on maintaining gas turbine shaft speed, safe operation was found to occur for expected ambient pressure variation ranges and for ambient temperature variations up to 28 K, when tested non-simultaneously. When ambient temperature and pressure were varied simultaneously, stable operation was found to occur when the two are in phase but not when the two are out of phase. The latter case leads to shaft over-speed. Compressor surge was found to be more likely when the system is subjected to a load shed initiated at minimum ambient temperature rather than at maximum ambient temperature. Fuel cell electrolyte temperature was found to be well-controlled except in the case of shaft overspeeds. Turbine inlet temperature remained in safe bounds for all cases. Copyright © 2009 by ASME.

A model of a photovoltaic (PV) powered residence in stand-alone configuration was developed and evaluated. The model assesses the sizing, capital costs, control strategies, and efficiencies of reversible fuel cells (RFC), batteries, and ultra-capacitors (UC) both individually, and in combination, as hybrid energy storage devices. The choice of control strategy for a hybrid energy storage system is found to have a significant impact on system efficiency, hydrogen production and component utilization. A hybrid energy storage system comprised of batteries and RFC has the advantage of reduced cost (compared to using a RFC as the sole energy storage device), high system efficiency and hydrogen energy production capacity. A control strategy that preferentially used the RFC before the battery in meeting load demand allows both grid independent operation and better RFC utilization compared to a system that preferentially used the battery before the RFC. Ultra-capacitors coupled with a RFC in a hybrid energy storage system contain insufficient energy density to meet dynamic power demands typical of residential applications. © 2006 Elsevier B.V. All rights reserved.

A dynamic model of a 100 MW solid oxide fuel cell-gas turbine hybrid system has been developed and subjected to perturbations in diurnal ambient temperature and pressure as well as load sheds. The dynamic system responses monitored were the fuel cell electrolyte temperature, gas turbine shaft speed, turbine inlet temperature, and compressor surge. Using a control strategy that primarily focuses on holding fuel cell electrolyte temperature constant and secondarily on maintaining gas turbine shaft speed, safe operation was found to occur for expected ambient pressure variation ranges and for ambient temperature variations up to 28 K when tested nonsimultaneously. When ambient temperature and pressure were varied simultaneously, stable operation was found to occur when the two are in phase but not when the two are out of phase. The latter case leads to shaft overspeed. Compressor surge was found to be more likely when the system is subjected to a load shed initiated at minimum ambient temperature rather than at maximum ambient temperature. Fuel cell electrolyte temperature was found to be well-controlled except in the case of shaft overspeeds. Turbine inlet temperature remained in safe bounds for all cases. © 2011 American Society of Mechanical Engineers.

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. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Solid oxide fuel cell-gas turbine (SOFC-GT) hybrid systems are attractive for future power generation with ultra-low criteria pollutant and greenhouse gas emissions. One of the challenges for SOFC-GT systems is to sufficiently pre-heat incoming air before it enters the fuel cell cathode. An ejector for cathode exhaust recirculation has the benefits of reliability, low maintenance, and cost compared to either recuperators or cathode recirculation blowers, which may be also be used for air pre-heating. In this study, a dynamic Simulink model of an ejector for cathode exhaust recirculation to pre-heat incoming fuel cell air has been developed. The ejector is to be utilized within a 100 MW SOFC-GT dynamic model operating on coal syngas. A thorough theoretical development is presented. Results for the ejector were found to be in good agreement with those reported in literature. © 2011 American Society of Mechanical Engineers.

A 100 MW-class planar solid oxide fuel cell synchronous gas turbine hybrid system has been designed, modeled, and controlled. The system is built of 70 functional fuel cell modules, each containing 10 fuel cell stacks, a blower to recirculate depleted cathode air, a depleted fuel oxidizer, and a cathode inlet air recuperator with bypass. The recuperator bypass serves to control the cathode inlet air temperature, while the variable speed cathode blower recirculates air to control the cathode air inlet temperature. This allows for excellent fuel cell thermal management without independent control of the gas turbine, which at this scale will most likely be a synchronous generator. In concept the demonstrated modular design makes it possible to vary the number of cells controlled by each fuel valve, power electronics module, and recirculation blower, so that actuators can adjust to variations in the hundreds of thousands of fuel cells contained within the 100 MW hybrid system for improved control and reliability. In addition, the modular design makes it possible to take individual fuel cell modules offline for maintenance while the overall system continues to operate. Parametric steady-state design analyses conducted on the system reveal that the overall fuel-to-electricity conversion efficiency of the current system increases with increased cathode exhaust recirculation. To evaluate and demonstrate the conceptualized design, the fully integrated system was modeled dynamically in MATLAB-SIMULINK. Simple proportional feedback with steady-state feed-forward controls for power tracking, thermal management, and stable gas turbine operation were developed for the system. Simulations of the fully controlled system indicate that the system has a high efficiency over a large range of operating conditions, decent transient load following capability, fuel and ambient temperature disturbance rejection, and the capability to operate with a varying number of fuel cell modules. The efforts here build on prior work and combine the efforts of system design, system operation, component performance characterization, and control to demonstrate hybrid transient capability in large-scale coal synthesis gas-based applications through simulation. Furthermore, the use of a modular fuel cell system design, the use of blower recirculation, and the need for integrated system controls are verified. © 2010 by ASME.