NUMERICAL INVESTIGATION OF A STAND-ALONE SOLAR HYDROGEN ENERGY SYSTEM: EFFECTS OF PEFC DEGRADATION
An existing stand-alone solar energy system producing hydrogen for energy storage is numerically investigated focusing on the degradation of Polymer Electrolyte Fuel Cell (PEFC) and its effects on the overall performance of the system. The system consists of Photovoltaic (PV) panels, polymer electrolyte based electrolyzers, H2 and O2 storage tanks and a commercial PEFC stack. A PEFC is numerically investigated both as new and as degraded (for about two years). Using a variety of observed degradation patterns reported in the literature, the degraded PEFC is parametrically analyzed by using ANSYS Fluent. The investigated parameters are the membrane equivalent weight, the Catalyst Layer (CL) porosity and viscous resistance, the Diffusion Layer (GDL) porosity and viscous resistance, and the bipolar plate contact resistance. By comparing the simulation results for the new and the degraded fuel cells, it is concluded that the effects of overall degradation on cell potential is significant -- being about 20% around the operating point of the fuel cell. This degraded fuel cell is incorporated into the TRNSYS model of the energy system, and then the effects of the PEFC degradation on the performance of the energy system are estimated. It is observed that the degradation has substantial impact on the overall system performance. System down time of approximately one month is possible. Thus, the stand-alone system is not capable of operating continuously for a complete year when the polymer electrolyte based components are degraded.