Fuel economy analysis of fuel cell and supercapacitor hybrid systems

Fuel cells generally have a higher energy density by a lower power density than batteries, and a fluctuating load can cause unstable operation as well as low efficiency. A hybrid in which a fuel cell is combined with an energy storage element with higher power density, such as a battery or supercapacitor, can enhance the load-following capability of a fuel cell system. We analyze the design space of a proton exchange membrane fuel cell (PEMFC) and supercapacitor hybrid system, and forecast the break-even operating period of the hybrid, at which the additional cost of hybridization is met by reduced fuel costs. The combination of a 100 W PEMFC and a supercapacitor with the earliest cost break-even time uses 6.8% less fuel than a base fuel cell, and has a 50% higher peak power capacity. The additional supercapacitor cost for hybridization is recoverable in 1152-6480 h of operation, while the typical guaranteed lifetime of a commercial fuel cell is around 3000 h.