Energy storage characterization for a direct methanol fuel cell hybrid system

This paper describes the energy storage characterization for a direct methanol fuel cell (DMFC) hybrid system for light traction applications. In a first step, the DMFC stack and the energy storage were dimensioned. To dimension the energy storage, the required energy density and power density were calculated. These are influenced by the operating states of the vehicle as well as the highly fluctuating load profile. For this kind of application a high energy density as well as a high power density is needed. Therefore, super capacitors are not the energy storage of choice. As an alternative, suitable batteries were analyzed in terms of their behavior in the DMFC hybrid system. Therefore, a characterization procedure was developed consisting of five different tests. These tests were developed adapted to the requirements of the application. They help to characterize the battery in terms of energy content, high power capability during charge and discharge, thermal behavior and lifetime. The tests showed that all batteries have to be operated on a partial state of charge (pSOC) and a thermal management is very important. Especially lead-acid battery show an decrease in lifetime under a pSOC operation. Therefore, a lithium battery was identified as the suitable energy storage for the considered application.