Electrochemical Sensor for Power Control of a Micro Fuel Cell

Micro fuel cells can be used for autonomous energy systems are used for surveillance, wireless communication nodes and other power needs where there is no access to grid electricity. For small power levels (e.g. 10 W) a battery or supercapacitor pack is often used. For long runtimes there is, however, a need for a large battery. The idea of this autonomous system is to reduce the battery/supercap package and instead use a photovoltaic during the day to charge up the batteries. The fuel cell contributes in the event of bad weather conditions when the photovoltaic is unable to deliver enough energy for several days. The energy system comprises a battery package for storage of electrical energy, a photovoltaic module which delivers electricity to the battery pack, a fuel cell for backup delivery of electricity, and a power control electronics unit which transfers the power to the load. The simplified fuel cell system consists of a hydrogen storage tank (pressurized hydrogen or metal hydride), a pressure regulation valve, a control valve, and a fuel cell stack. Thanks to that the battery pack can handle load variations the fuel cell system can be adapted to run at a constant gas flow level. Thereby, the control valve can be reduced to an on-off valve, which means that simplified the fuel cell system can compete with the cost for batteries. This work will analyse how the voltage from an external fuel cell (short circuited over a resitor and fed by the hydrogen exhaust) can be used to control the power draw of the stack. The sensitivity to hydrogen flow variation, start-up and shut-down procedures will be investigated.