Physically consistent sectoral pathways for phasing out fossil fuels

The transition away from fossil fuels relies on a range of strategies, including deploying low-carbon, electricity-producing energy sources. To understand how much electricity is needed to substitute fossil fuels, sectors of the economy being electrified must be analysed discretely, as their suitability for electrification varies significantly. Constructing, operating, and maintaining these renewable power plants requires substantial amounts of energy. Here, we propose a model which calculates the electricity required to electrify each major sector, and quantifies the energy required to deploy the renewable power plants producing this electricity. We apply this model to the European Union across scenarios phasing out fossil fuels by 2035, 2050, 2075, and 2100. We find that transition energy requirements increase with transition speed and that they are greater than the current energy spent on obtaining fossil fuels in the more ambitious scenarios. We also reveal the energy requirements of each sector, disaggregated into categories (power plants, grid extensions, and end-use devices) allowing for a comparative analysis of their relative significance. We produce quantitative evidence supporting the emerging conceptual consensus that a rapid energy transition will require reallocating significant amounts of energy from other end uses to transition-related uses. This could lead to societal disruptions, as part of some energy-dependent services (e.g., transport, residential heating, manufacturing etc.) will have to be forgone to carve an energy budget for the transition. Our model can provide a quantitative basis for assessing these disruption risks, and support policy- and decision-making to mitigate them. • A model to estimate transition energy requirements to electrify all fossil fuel uses. • Fast energy transitions consume a significant fraction of the total energy supply. • On average, 1 unit of fossil fuel energy is substituted by 0.71 units of electricity. • Favoring hydrogen over electricity increases energy requirements by 22 %. • Targeted sufficiency in hard-to-electrify sectors can facilitate a faster transition.