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The European Union’s rapid expansion of solar and wind power must be matched by investment in clean firm power and long-duration energy storage if the bloc is to deliver affordable, reliable and zero-carbon electricity, a new report says.
Clean firm power refers to zero- or low-carbon electricity that can be supplied on demand around the clock, independent of weather conditions.
The report by climate innovation think tank Future Cleantech Architects says variable renewable energy will dominate Europe’s future power system because of falling costs and rapid deployment. But it warns that solar and wind alone cannot guarantee supply during prolonged periods of low generation, especially as electricity demand rises from electrification, industry and data centres.
The report, Clean Firm Power: Complementing Variable Renewables and Storage for a Fossil-Free Power System, was launched at the Future Cleantech Festival in Remscheid, Germany. It says Europe must reduce fossil fuel dependence, strengthen energy security and lower power costs while preparing for periods known in the energy sector as “Dunkelflaute” — stretches of several days or weeks when wind and solar output are both low.
It comes as Europe faces rising electricity demand from electrification, industry and data centres while seeking to reduce fossil fuel dependence, strengthen energy security and lower power costs.
Batteries, renewable overcapacity and short-duration storage can manage most short-term fluctuations, the report says, but are not enough to cover longer supply gaps.
“There are no cheaper forms of electricity when the sun is shining and the wind is blowing,” said Antoine Koen of Future Cleantech Architects. “Yet it is unrealistic to try and build enough overcapacity of wind and solar to cover infrequent yet crucial periods over several days when they produce nearly no energy at all.”
“Europe needs to complement variable renewables by building clean firm power at scale and at speed, he added”
The report identifies three clean firm power technologies as central to a fossil-free electricity system: next-generation geothermal energy, hydropower and nuclear power. It says next-generation geothermal energy could become an important source of electricity and heat by drawing on expertise and infrastructure from the oil and gas sector.
According to FCA, Europe’s technical geothermal potential is equivalent to 35 times the continent’s current installed electricity generation capacity. Geothermal energy could also provide direct heat for industrial processes and district heating networks, the report says.
Hydropower remains one of Europe’s most established low-carbon and flexible energy sources. While geography limits major expansion, the report says existing hydropower facilities should be modernised and upgraded to preserve and strengthen their role in grid flexibility.
The report also highlights nuclear power’s ability to provide reliable low-carbon electricity and industrial heat. It says future deployment could include both conventional nuclear plants and Small Modular Reactors, if Europe moves beyond isolated projects and develops larger-scale programmes.
The report is accompanied by public opinion research conducted by Project Tempo. A representative survey of more than 4,000 Germans in May 2026 found that 65 per cent supported building more solar power in their region, while 45 per cent supported additional geothermal projects.
Geothermal energy had relatively consistent support across the political spectrum, the survey found. By contrast, views on nuclear power and onshore wind projects remained divided along partisan lines.
FCA says market forces alone are unlikely to deploy capital-intensive clean firm power technologies at the speed and scale required.
It calls on EU policymakers to include clean firm power in decarbonisation, energy and industrial strategies.
It also recommends electricity market reforms so technologies can compete on carbon intensity, reliability and flexibility.
Other recommendations include expanding public guarantees and blended finance for first-of-a-kind projects, increasing support through Horizon Europe and the EU Innovation Fund, speeding up permitting and grid connections, and coordinating deployment across member states to strengthen supply chains and lower costs.
The report broadly rejects carbon capture and storage and bioenergy as priority pathways for Europe’s future electricity system, while supporting long-duration storage alongside clean firm power.
It concludes that Europe’s energy transition will need a portfolio approach combining solar, wind, batteries, demand flexibility, grid expansion, long-duration storage and clean firm power to deliver a fully decarbonised and reliable power system.