Complete electrification worsens the net energy prospects of a transition based on wind and solar energy.

Mitigating climate change largely relies on substituting fossil fuels with low-carbon, electricity-producing energy sources. This mass electrification deeply alters sectoral energy demand, as some sectors can be more efficiently electrified than others. Building transition infrastructure – such as solar and wind farms, grid extensions, and electric vehicles – at a sufficient pace to achieve ambitious transition plans requires significant amounts of energy, potentially causing societal disruptions. We develop a framework to assess how mass electrification will affect transition energy requirements by disaggregating them into sectors and assigning them electrification efficiencies. We apply this model to the European Union (EU-27) under a scenario phasing out fossil fuels by 2050. We find that sectors employed to build transition infrastructure are more difficult to electrify than the economy-wide average. Mass electrification therefore increases transition energy requirements relative to supply, exacerbating net energy challenges. We also find that, depending on the order in which sectors are electrified, transition-related demand for coal (linked to steel production for wind turbines) can be significant compared to its supply, suggesting coal can be a critical material. Our results show that improving the electrification efficiency of sectors used in the transition significantly improves net energy prospects, hence we suggest prioritising battery electric trucks and industrial heat pumps over their less efficient hydrogen-powered alternatives. By capturing sector- and vector-specific dynamics, our analysis identifies previously undocumented net-energy challenges and actionable levers to mitigate them. These results highlight the importance of physically consistent transition models to guide the energy transition.