Optimal Energy Harvesting From Serially Connected Microbial Fuel Cells

Microbial fuel cell (MFC) converts electrochemical energy from organic matter into electricity by means of chemotrophic bacteria metabolisms. The MFC power output is limited in voltage and in current in the range of microwatts or milliwatts per liter. The output power may be improved by association of MFCs either in series or in parallel. The serial association of a large number of MFCs presents a benefit in effective output voltage but may suffer from several limitations. The most important is that the possible dispersion between the microgenerators leads to a nonoptimal stack efficiency. A power management unit is also necessary to harvest energy from a single MFC or a group of connected MFCs. The converter functions are to step up the voltage and to control the operating point of the MFC(s). The aim of this paper is to build an appropriate architecture for energy harvesting from series-connected MFCs, which feature disparate behaviors. A system to meet low-power sensor consumption specifications is composed of a stack of nonuniform serially connected MFCs, a voltage balancing circuit, and a maximum power point converter. The system is designed, fabricated, and tested. A percent of maximum power achieved of 86% is demonstrated for 1.5 mW of harvested power from four MFCs with large dispersion in characteristics.