Efficiency Increase of Biological Methanation based Power-to-Methane Technology Using Waste Heat Recovery with Organic Rankine Cycle

Due to the efforts of reducing greenhouse gas emissions, nearly two-thirds of the installed electric capacity worldwide will come from renewables in 2050 (EIA 2021), making frequency control without energy storage impossible. Power-to-Methane (PtM) technology allows electricity to be stored in the form of methane. The storage efficiency of PtM may be increased either by maximizing the recovery of the stored electricity, which is a common method, or by reducing the amount of electricity the PtM has to be charged with for a given amount of stored energy. In this paper, a case study is presented for the latter by directly integrating an Organic Rankine Cycle into the PtM technology by recycling the waste heat from water electrolysis and biological methanation back to electrolysis. With this method, total storage efficiency can be increased by approximately two percentage points.