Simplified modelling of nonlinear electromethanogenesis stack for power-to-gas applications

Bioelectrochemical systems performing electromethanogenesis (EMG-BES) represent an emerging technology for Power-to-gas as well as wastewater treatment. Moreover, EMG-BES can be used as a high-capacity energy storage system to absorb surplus energy in the electrical grid. This paper presents a modelling approach, which is based on building an equivalent electric circuit of the EMG-BES, which can be used to emulate static and dynamic non-linear behaviour of EMG-BES for different input voltages, which is advantageous if compared to other existing models. This model is a suitable choice for future studies in the development of the electric converters for EMG-BES plants connected to the electrical grid. The proposed model consists of practical and commercial elements, including capacitors, resistors, voltage sources, and a diode. The modelling of non-linear behaviour is achieved by adding a diode to the model. Four simple tests were performed to determine the equivalent circuit parameters in a medium-scale EMG-BES prototype. This prototype was built by stacking 45 cells together and connecting them in parallel, and it was long-term operated and tested under different electric inputs to determine the model parameters. A comparative study was finally conducted as reported in this paper in order to validate the proposed model against experimental results and values collected with other models.