Results of a 20 000 h lifetime test of a 7 kW direct methanol fuel cell (DMFC) hybrid system – degradation of the DMFC stack and the energy storage
With a proven life of 20 000 operation hours in a lifetime test with a realistic dynamic load profile, the direct methanol fuel cell (DMFC) system V3.3-2 represents a milestone for the commercialization of DMFC systems. The hybrid DMFC system V3.3-2 comprises an in active serial connected 1.0 kW DMFC system and a 45 A h lithium-ion high-power battery pack. This hybrid system replaces the battery tray of a class 3 forklift truck and can supply a peak load of 7 kW. The advantages of this energy-supply module compared to conventional lead-acid batteries are its higher range (24 h use with a 20 L methanol canister instead of 8 h with battery recharging) and its higher availability (a few minutes are required to exchange methanol canisters instead of hours to recharge the battery). However, in order to ensure that use of the DMFC system V3.3-2 is economic, the DMFC stack must have a durability of at least 10 000 h. This publication describes the degradation behavior of the DMFC stack and of the energy storage system during a lifetime test of the DMFC system V3.3-2 with a dynamic load profile of a material handling vehicle. In the first-ever test worldwide lasting 25 600 h, the hybrid system is successfully operated for 20 000 h. Operation for 20 000 hours is equivalent to the life cycle of a vehicle in the material handling sector. The development and validation of the DMFC system V3.3-2 shows that this system is suitable for use in a forklift truck and that it not only meets the economic system requirements for commercialization but goes well beyond them.