Study on capacity optimization of PEM fuel cell and hydrogen mixing gas-engine compound generator

Development of a small-scale power source not dependent on commercial power may result in various effects. For example, it may eliminate the need for long distance power-transmission lines, and mean that the amount of green energy development is not restricted to the dynamic characteristics of a commercial power grid. Moreover, the distribution of the independent energy source can be optimized with regionality in mind. This paper examines the independent power supply system relating to hydrogen energy. Generally speaking, the power demand of a house tends to fluctuate considerably over the course of a day. Therefore, when introducing fuel cell cogeneration into an apartment house, etc., low-efficiency operations in a low-load region occur frequently in accordance with load fluctuation. Consequently, the hybrid cogeneration system (HCGS) that uses a solid polymer membrane-type fuel cell (PEM-FC) and a hydrogen mixture gas engine (NEG) together to improve power generation efficiency during partial load of fuel cell cogeneration is proposed. However, since facility costs increase, if the HCGS energy cost is not low compared with the conventional method, it is disadvantageous. Therefore, in this paper, HCGS is introduced into 10 household apartments in Tokyo, and the power generation efficiency, carbon dioxide emissions and optimal capacity of a boiler and heat storage tank are investigated through analysis. Moreover, the system characteristics change significantly based on the capacity of PEM-FC and NEG that compose HCGS. Therefore, in this study, the capacity of PEM-FC and that of NEG are investigated, as well as the power generation efficiency, carbon dioxide emissions and the optimal capacity of a boiler and heat storage tank. Analysis revealed that the annual average power generation efficiency when the capacity of PEM-FC and NEG is 5 kW was 27.3%. Meanwhile, the annual average power generation efficiency of HCGS is 1.37 times that of the PEM-FC independent system, and 1.28 times that of the NEG independent system, respectively.