Clean Firm Power in Europe’s Energy Transition: Evidence, Constraints, and System Roles

Across models and regions, the precise choice of clean firm technology matters less than the presence of some form of dispatchable, low-carbon capacity capable of sustaining output during extended periods of low renewable generation. What the evidence shows is that system reliability hinges on the function such resources provide, not on whether that function is delivered by advanced geothermal, nuclear, CCS-enabled gas, hydrogen turbines, or long-duration storage substitutes. It is worth noting that geothermal, despite being a potentially attractive clean-firm option in some regions, is only rarely included in European modelling studies.

Although the literature does not converge on a single optimal portfolio, the reviewed studies consistently show that decarbonised systems require firm, weather-independent resources to maintain adequacy, moderate system costs, and limit infrastructure burdens (overbuilt). The specific technologies, nuclear, geothermal, CCS-equipped gas or biomass, reservoir hydropower or hydrogen-fired turbines, vary across countries according to political preferences and resource availability, but their system function is broadly interchangeable.

Importantly, studies that incorporate realistic constraints such as sector coupling, land availability, import risks, and multi-decadal weather variability converge on a stronger and more persistent role for clean firm power. In this sense, the mix is not standardised, but the need for firm, dispatchable, low-emission capacity is a robust and recurring feature of credible European net-zero pathways. Finally, this review has mapped the modelling approaches used across the reviewed studies. A deeper understanding of the role of clean-firm power will require broader incorporation of price volatility, self-sufficiency metrics, and, in particular, higher spatial resolution, which most studies have lacked until now.