DYNAMIC BEHAVIOR OF A SOLID OXIDE STEAM ELECTROLYZER SYSTEM USING TRANSIENT PHOTOVOLTAIC GENERATED POWER FOR RENEWABLE HYDROGEN PRODUCTION

The purpose of this study is to investigate the dynamic behavior of a Solid Oxide Steam Electrolyzer (SOSE) system without an external heat source which uses transient photovoltaic (PV) generated power as an input to produce compressed (to 3MPa) renewable hydrogen to be injected directly into the natural gas network. A cathode-supported crossflow planar Solid Oxide Electrolysis (SOE) cell is modeled in a quasi-3D thermo-electrochemical model that spatially and temporally simulates the performance of a unit cell operating dynamically. The stack is comprised of 2500 unit cells that are assumed to be assembled into identically operating stacks, creating a 300kW electrolyzer stack module. A 15-minute resolution dataset for operation of PV generation was obtained from a database that archives PV power dynamics of systems on the University of California, Irvine campus. The dataset (comprised of data for approximately 4.1 MW of peak solar power) was scaled to a maximum of 450kW of PV generation. For the designed 300kW SOSE stack (thermoneutral voltage achieved at design steady state conditions), powered by the dynamic 0-450kW output of PV systems, thermal management and balancing of all heat supply and cooling demands is required based upon the operating voltage to enable efficient operation and prevent degradation of the SOSE stacks. The PV generation dataset was analyzed to obtain a day in which the PV generated power has its highest dynamic behavior (a cloudy day) and another day in which the PV generated power and energy is maximum (a sunny day). Dynamic system simulation results show that the SOSE system is capable of following the dynamic PV generated power for both of these days while the SOSE stack temperature gradient is always maintained below a maximum set point along the stack for both days. The system efficiency based upon lower heating value of the generated hydrogen is between 0-75% and 0-78% with daily hydrogen production of 94kg and 55kg for sunny and cloudy days, respectively.