Environment (Commonwealth Union) – Recent research conducted at the Imperial College London finds that phasing out fossil fuels across the European Union will require a large amount of so-called “transition energy,” with faster timelines demanding much greater—and potentially disruptive—shifts in how energy is allocated across society.
Using a model that estimates the electricity needed to replace fossil fuels in key sectors such as transport and heating, alongside the energy required to construct the necessary infrastructure, the research suggests that current approaches to net-zero are incomplete. The findings point to the need for coordinated action across industries and, at least temporarily, reductions in non-essential energy use, including air travel, driving, and the production of non-essential goods.
The lead author Ugo Legendre, a PhD researcher in Imperial’s Department of Earth Science and Engineering indicated that a credible energy transition plan comes with a significant upfront energy cost, that cost is driven by the energy required to build the systems that enable renewable power, from generation facilities to expanded electricity grids.
“However, these energy requirements are typically absent in mainstream discussions about the energy transition that concern the public, politics and even the economy, despite costs increasing as we look to faster transition scenarios, such as by 2050.
“In accounting for all types of infrastructure and their energy requirements, our work has quantified this massive, understudied effort, which must be planned for and inevitably involves a trade-off with the energy we currently use in our daily lives.”
Moving the global economy away from fossil fuels depends on constructing entirely new energy systems. That process itself demands a vast amount of energy upfront, as society must manufacture technologies such as wind turbines and solar panels. This initial investment—known as ‘transition energy’.
To explore the demands and constraints of rapid energy transition pathways, the researchers developed a model that first assesses how effectively electricity can replace fossil fuels across key economic sectors. Depending on the targeted speed of the phase-out, the model estimates the extra electricity that must be generated each year. It then calculates the scale of infrastructure required to generate, deliver and use that electricity, along with the materials involved, before finally accounting for the energy needed to extract, process and transport those materials.
When applied to four EU fossil fuel phase-out timelines—2035, 2050, 2075 and 2100—the model shows that faster transitions require substantially more energy to construct a low-carbon system. The findings, published in Renewable and Sustainable Energy Reviews, reveal a clear link between transition speed and energy intensity.
Under the most aggressive scenario, which eliminates fossil fuels by 2035, annual transition energy demand would peak at the equivalent of 39% of the EU’s current total energy supply. Even when spread more evenly over time, the requirement remains high at around 25%. For a 2050 phase-out, the corresponding figures fall to 24% at peak and 19% on average.
The co-author Dr Pablo Brito Parada, Associate Professor in Sustainable Minerals Processing in the Department of Earth Science and Engineering indicated that the critical part is that in the quicker scenarios, this transition energy goes beyond the energy they spend at present on simply extracting and refining fossil fuels – which makes them divert significant quantities of energy from transport, manufacturing or heating homes and offices which was given as an example.
Dr Parada further indicated that rolling out infrastructure at such scale demands a similarly wide-ranging and substantial upfront energy input, which could temporarily reduce the net energy available for other uses. He pointed out that at the same time, energy will still be required to extract fossil fuels throughout the transition period and as the electricity system shifts toward a higher proportion of intermittent renewable power, additional losses from curtailment and storage inefficiencies will further diminish the usable energy supply.
