Towards effective energy harvesting from stacks of soil microbial fuel cells

The 2050 net-zero carbon target can only be achieved with renewable energy solutions that can drastically reduce carbon emissions. Soil microbial fuel cells (SMFCs) have significant potential as a low-cost and carbon-neutral energy conversion technology. Finding the most practical and energy efficient strategy to operate SMFCs is crucial for transitioning this technology from the lab to field implementations. In this study, an innovative self-sustaining and model-based energy harvesting strategy was developed and tested for the first time on SMFC stacks. The model, based on a first-order equivalent electrical circuit (EEC), enables real-time and continuous maximum power point tracking, without the need for offline analysis of electrochemical parameters. Power extraction from the SMFCs to fully charge a 3.6 V NiMH battery, was carried out for 24 h: the longest test duration reported so far on biological fuel cells for such energy harvesting strategy. A novel second-order EEC was also proposed to better describe the electrical dynamics of the SMFC. Our results provide important advances on both accurate model-based electrochemical parameter identification techniques and maximum power point tracking algorithms, for optimal energy extraction from SMFCs. Consequently, this study paves the way for successful implementations of SMFCs towards viable green energy solutions.