Germany leads Europe in power-to-gas (P2G) solutions – the production of hydrogen or renewable methane gas from excess electricity. Scientists from the Friedrich-Alexander University of Erlangen-Nuremberg and the Technical University of Ingolstadt in Bavaria have teamed up with Regineering GmbH to explore how the carbon dioxide produced in small agricultural biogas plants could be converted into methane using renewable energy sources.
Critically, the methane could then be stored decentrally – not fed back into the grid – for use directly on site in combined heat and power (CHP) generation. This P2G process has already been integrated into larger plants, but has not been tested before in smaller plants, which may not have a direct connection to the gas grid, or else the cost of feed-in is too high.
The biogas produced in agricultural plants is rich in CO2. The gas is upgraded to biomethane through a process called ‘methanisation’. As the Agency for Renewable Resources explains, the biogas will first be discharged from the fermenter. Then its CO2 content will be catalytically reduced – this will be done when electricity is particularly cheap. The biomethane then ends up back in the gas bubble, where the methane content – and hence the energy content of the biogas – increases.
Presently, Germany’s Renewable Energy Sources Act (EEG) incentivises plants to generate renewables, but the subsidies will only run until 2021. This project will lay the groundwork for small biogas plants to be self-sufficient after the remuneration period runs out. The feasibility of the concept will be tested extensively before it is implemented in small biogas plants. The project is funded by the Federal Ministry of Food and Agriculture (BMEL).