Electrofuels from Excess Renewable Electricity at High Variable Renewable Shares: Cost, Greenhouse Gas Abatement, Carbon Use and Competition

Increasing shares of variable renewable electricity (VRE) generation are necessary for achieving high renewable shares in all energy sectors. This results in increased excess renewable electricity (ERE) at times when supply exceeds demand. ERE can be utilized as a low-emission energy source for sectorcouplingthroughhydrogenproductionviaelectrolysis, whichcanbeuseddirectlyorcombined 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). These counteracting effects for the electrofuel production have not been analysed before. Here we perform a model based analysis for the German case until 2050, with a general analysis for regions with a high VRE reliance. Results indicate that ERE-based electrofuels can achieveagreenhousegas(GHG)abatementof74MtCO2eqyearly(46%ofcurrentGermantransport emissions) by displacing fossil fuels, at high fuel-cell electric vehicle (FCEV) shares, at a cost of 250320 € t CO2eq−1. The capital expenditure of electrolysers was found not to be crucial for the cost, despitelowcapacityfactorsduetovariableEREpatterns. Carbonwilllikelybecomealimitingfactor when aiming for stringent climate targets and renewable electricity-based hydrocarbon electrofuels replacing fossil fuels achieve up to 70% more GHG abatement than CCS. Given (1) an unsaturated demandforrenewablehydrocarbonfuels,(2)asaturatedrenewablehydrogendemandand(3)unused ERE capacities which would otherwise be curtailed, we find that carbon is better used for renewable fuel production than being stored.