Europe lacks backup power for windless winter weeks, study finds

Europe's ambition to run on renewable electricity alone has a winter problem. When high pressure settles over the continent for days at a time, temperatures drop, heating demand surges, and the wind stops blowing. Solar panels contribute almost nothing in December and January. Batteries can cover hours, not weeks. The result, according to a new modelling study, is a gap that no amount of wind turbines or solar farms can fill, and that the backup plants needed to plug it cannot pay for themselves under today's market rules.

The summer that previewed the challenge

The research lands after a summer that already exposed the fragility of the existing system. Repeated heatwaves across the continent in 2026 lowered river levels and raised water temperatures to the point where nuclear reactors could not cool themselves. Hungary lost most of the output from the Paks plant on the Danube, a sizeable share of the country's electricity. In France, seawater-cooled stations had to throttle back because jellyfish, thriving in warmer water, clogged their intake screens. At the same time, tropical nights drove evening demand to record levels as households ran air conditioning deep into the night.

It was not the first warning. At the end of 2024, a prolonged period of low wind and weak sunshine across north-western Europe sent wholesale prices soaring and forced greater reliance on gas-fired generation and imports. The pattern has a name among researchers: energy droughts. These are episodes when both wind and solar output fall together, often across the whole interconnected European grid, leaving no neighbour with surplus power to share.

Eighty years of weather, one counterfactual grid

Researchers at the Technical University of Denmark and Newcastle University built a model of a European energy system with all fossil fuels removed, wind, solar, hydro, biomass and nuclear only, and stress-tested it against meteorological records from 1941 to 2021. The aim was not to forecast next winter but to see how a zero-emission grid would have coped with every documented combination of wind, sun, temperature and demand over eight decades.

The answer is sobering. The most dangerous periods are not heatwaves but winter cold spells lasting several days under stagnant high pressure. Wind output collapses across the North Sea, the Baltic and the continental interior simultaneously. Solar is negligible. Demand for heating peaks. Batteries, even at massive scale, exhaust themselves in hours. The only way through is dispatchable capacity that can run for days at a time: hydrogen turbines, gas with carbon capture, long-duration storage, or nuclear plants that are not constrained by cooling water.

The economics of idle steel

Here the study reaches its most uncomfortable conclusion. The backup capacity required to survive the worst weeks would sit unused for the vast majority of the year. In a market that pays only for energy produced, or even for capacity that is rarely called upon, the revenue stream is too thin to cover capital costs. Investors will not build plants that earn money perhaps once every few years. The result, the authors argue, is either a system that fails during the next energy drought or one that carries extremely high prices to subsidise standby capacity.

"We also found that the capacity required to keep the system secure during such periods is rarely used at other times," said Marta Victoria of DTU, one of the study's authors. "It is more expensive than renewables or other technologies, such as hydropower, making it difficult to finance under current market conditions and resulting in high electricity prices."

Short-term shocks versus long-term design

The researchers distinguish between two resilience challenges. Short-term resilience is the ability to ride out a sudden drop in renewable output lasting hours or days, a problem that batteries, demand response and interconnectors can largely solve. Long-term resilience is about whether the system as a whole is sized correctly to withstand the rare but inevitable multi-day energy droughts that occur once or twice a decade. The study shows that Europe is not there yet. The transmission grid, the mix of renewable technologies, the volume of storage and the quantity of firm low-carbon generation all fall short of what the model says is needed.

Aleksander Grochowicz, the study's lead author, put it this way: "From the perspective of the energy system, extreme weather therefore does not necessarily mean 'bad weather'." The system's breaking point is not a storm but a still, cold week in January. The complexity of a highly renewable grid, many technologies, many countries, many weather regimes, makes it hard to model but also gives it more ways to survive, provided the pieces are planned together rather than added piecemeal.

What the grid already knows

The historical record the model draws on is not abstract. January 2017 brought a cold spell with low wind and high heating demand that strained several national systems at once. In 2021, unusually low wind speeds across north-western and central Europe persisted for months, contributing to the price spike that preceded the gas crisis. These are not theoretical tail risks; they are documented events that a zero-emission grid would have to survive without the gas plants that bailed the system out last time.

Market design is the missing piece

The authors stop short of prescribing a single technology for backup. Hydrogen-fired turbines, long-duration thermal storage, advanced nuclear, gas with carbon capture, all are candidates. What they insist on is a market framework that pays for availability, not just output. Capacity mechanisms exist in several member states but are fragmented, often controversial, and not designed for a continent-wide energy drought. A European approach, coordinated through the European Commission's energy directorate and the European Network of Transmission System Operators, would be a logical step but remains politically fraught.

The study also notes that the expansion of renewables must continue. Wind and solar remain the cheapest bulk energy and the foundation of energy independence. The problem is not generation but the insurance policy. "We need to think more carefully about resilience during short periods when renewable sources are insufficient, and about how much we are willing to pay for it," Victoria said. "Better planning encourages investment and improves energy security, making the costs worthwhile."

Cooling water: the hidden constraint

The summer 2026 episode adds a further twist. Nuclear power, often cited as the firm low-carbon backbone of a renewable grid, has its own climate vulnerability. River-cooled plants face lower flows and higher inlet temperatures. Seawater-cooled plants face biological fouling. The Paks shutdown in Hungary and the jellyfish-related curtailments in France are not modelled in the DTU study, which assumes present-day climate conditions but a fully sustainable fuel mix. If cooling constraints tighten further, the amount of firm capacity available in summer, and therefore the margin for winter, shrinks.

The next decision point

The European Commission is due to publish its assessment of capacity mechanisms and resource adequacy by the end of 2026. That review will be the first test of whether Brussels accepts the study's premise: that a unified European backup strategy, paid for by all consumers, is cheaper than national scrambles when the wind stops. Meanwhile, the International Energy Agency has flagged the same issue in its latest electricity market report, noting that firm capacity investment is lagging behind renewable additions across advanced economies. The numbers from DTU give both institutions a concrete basis for a conversation that has so far been conducted in generalities.