A portable hybrid hydrogen fuel cell-battery power unit for wireless sensor network

Hydrogen fuel cells are considered one of the most promising alternatives to batteries, because of their higher energy density and they are not affected by issues related to self-discharge. Fuel cells are very attractive for devices with long lifetime requirements. Unfortunately, fuel cells suffer from slow dynamic response to load changes and require active gas flow control. These issues have not been previously addressed for portable systems and small scale fuel-cells. This work presents a hybrid hydrogen micro fuel cell/ Li-Ion battery power unit for embedded systems and wireless sensor networks which tackles these issues. The power system is microcontroller-based and it provides a driver circuits to control the hydrogen flow closing and opening an electro-valve certified for hydrogen gas. We first describe the fuel cell implementation we characterize its power delivery capability. Next, we present the architecture of the developed prototype for the power unit and the fuel flow control system. Finally an evaluation of the performance during Li-Ion battery recharges is presented. The behaviour of hybrid system is examined and tested and the experimental results show the high efficiency (around 85\%) of the proposed solution. A 1000mAh Li-Ion battery is re-charged with 11liters of hydrogen in around 2 hours.