Nuclear operations with a high penetration of renewables: the case of France

Résumé

A low-carbon electricity sector may rely on intermittent renewables, nuclear or both. This paper explores the latter option, for which the (lack of) ability of nuclear units to adjust output in the short-run can have a significant impact on electricity prices, and therefore on the long-term profitability of assets generating or consuming electricity. Our analysis focuses on France, a country with a nuclear capacity of 63GW and a total capacity of wind and solar of about 50GW as of 2025. We first document that, in contrast to widely held beliefs, nuclear units can be operated flexibly: an additional 1MWh of domestic wind and solar generation is on average associated to a 0.6MWh decrease in nuclear output. We next explore the potential opportunity costs associated with flexible nuclear operations. Finally, we show that the available downward flexibility of the nuclear fleet is limited by increasingly binding operating constraints: in 2024, hours during which available nuclear flexibility was exhausted are strongly associated with zero or negative prices.