Long-Term Economic Analysis and Optimization of an HT-PEM Fuel Cell based Micro Combined Heat and Power Plant

Multi-objective optimization method using genetic algorithm is employed in order to optimize design and operating parameters of a high temperature proton exchange membrane (HT-PEM) fuel cell based combined heat and power system. Net electrical efficiency of the plant, indicating the system's performance (to be maximized) and the total capital cost (to be minimized) are considered as optimization objectives. Current density (indicating the stack size), steam to carbon ratio, burner outlet temperature and auxiliary to process fuel ratio have been chosen as design parameters. Two different multi-objective optimization approaches have been utilized: steady state (without degradation) and long-term optimization while considering the degradation in fuel cell stack and the fuel processor. The results of the optimization procedures are Pareto frontiers which are a set of optimal points each of which is a trade-off between the considered objective functions. The performance indexes and operating conditions of three points with the maximum cumulative net electrical efficiency, minimum capital cost, and the same fuel cell area as that of the initial design are compared. It can be observed that while attempting to maximize the electrical efficiency, the cumulative net electrical efficiency of 29.96% can be achieved although it results in a total capital cost of 115711 €. On the other hand, the capital cost can be reduced down to 39,929 € which significantly diminishes cumulative net electrical efficiency. Finally, by locating the point on the Pareto frontier in which the fuel cell area is the same as that of the initial design, a cumulative net electrical efficiency of 27.07% was achieved which is 1% higher than the value obtained using the operating conditions of the initial design.