What is the energy balance of electrofuels produced through power-to-fuel integration with biogas facilities?

The need to reduce the climate impact of the transport sector has led to an increasing interest in the utilisation of alternative fuels. Producing advanced fuels through the integration of anaerobic digestion and power-to-fuel technologies may offer a solution to reduce greenhouse gas emissions from difficult to decarbonise modes of transport, such as heavy goods vehicles, shipping, and commercial aviation, while also offering wider system benefits. This paper investigates the energy balance of power-to-fuel (power-to-methane, power-to-methanol, power-to-Fischer-Tropsch fuels) production integrated with a biogas facility co-digesting grass silage and dairy slurry. Through the integration of power-to-methane with anaerobic digestion, an increase in system gross energy of 62.6% was found. Power-to-methanol integration with the biogas system increased the gross energy by 50% while power-to-Fischer-Tropsch fuels increased the gross energy yield by 32%. The parasitic energy demand for hydrogen production was highlighted as the most significant factor for integrated biogas and power-to-fuel facilities. Consuming electricity that would otherwise have been curtailed and optimising the anaerobic digestion process were identified as key to improving the energetic efficiency of all system configurations. However, the broad cross-sectoral benefits of the overarching cascading circular economy system, such as providing electrical grid stability and utilising waste resources, must also be considered for a comprehensive perspective on the integration of anaerobic digestion and power-to-fuel.