Electrofuels from excess renewable electricity: costs, emissions, carbon use

Large shares of variable renewable electricity (VRE) generation are pursued in order to achieve emissions targets in the energy sectors. This results in increased excess renewable electricity (ERE) at times when supply exceeds conventional inflexible electricity demand. ERE can be utilized as a low-emission energy source for sector coupling through e.g. hydrogen production via flexible electrolysis, Which can be used directly or combined With a carbon source to produce electrofuels. Such fuels are crucial for the transport sector, where renewable alternatives are scarce. However, while ERE increases With raising VRE shares, carbon emissions decrease and may become a limited resource with several usage options, including carbon storage (CCS). Here We perform a model based analysis for the German case until 2050, with a general analysis for regions with a high VRE reliance. The capital expenditure of electrolysers was found not to be crucial for the cost, despite low capacity factors due to variable ERE patterns. Carbon will likely become a limiting factor when aiming for stringent climate targets and renewable electricity-based hydrocarbon electrofuels replacing fossil fuels achieve up to 70% more greenhouse gas (GHG) abatement than CCS. Given (1) an unsaturated demand for renewable hydrocarbon fuels, (2) a saturated renewable hydrogen demand and (3) unused ERE capacities which would otherwise be curtailed, we find that carbon used for renewable fuel production abates more GHG than if the carbon would be stored. This effect may increase substantially if shale oil or gas is displaced.