Modeling Solar Hydrogen Fuel Cell Systems 1

In this study a solar hydrogen fuel cell system (SH₂FCS) was modeled to help understand the behavior of, and to aid in the optimal design of, such systems at different load and ambient conditions. The main components of this system are photovoltaic modules, solid polymer electrolyte (SPE) water electrolyzers, proton exchange membrane (PEM) fuel cells, and hydrogen and oxygen storages devices. All the models are based on physical and electrochemical principles, as well as empirical relationships. The thermal model of SPE electrolyzer, PEM fuel cell, and tank storage are developed using the lumped parameter approach. A high-pressure electrolyzer is used instead of a compressor to reduce the parasitic loads. A unique approach of placing the electrolyzer in the hydrogen storage tank to prevent leaks from the electrolyzer was modeled (patent applied for). The power management of the system is achieved using an on-off controller; and the control of the temperature for the electrochemical devices is performed using a proportional integral controller strategy. Other actual solar hydrogen systems (i.e., Schatz Solar Hydrogen Project at Humboldt University and the PHOEBUS plant at FZ-Julich in Germany) were simulated, and results were compared to help verify the model. Some laboratory test data was also used to formulate 372and verify the electrolyzer model. A system was sized and simulated with actual weather and load data monitored at a remote medical clinic in the mountains of Peru. Good temperature control and energy management performance resulted. Water recirculated through the electrolyzer was found important to keep the electrolyzer cool enough. The energy needed to compress hydrogen using the electrolyzer as a compressor is less than the mechanical energy required for a compressor. The simulated overall energy efficiency of the regenerative fuel cell system (electrolyzer, gas storage, and fuel cell) is relatively low at about 42%. This model will aid in the optimization of the sizing/design of the SH₂FCS to improve the energy efficiency and reduce costs.