October 2026
This written evidence submission, developed with partners at University College London, responds to the inquiry’s questions regarding how the UK can maintain a secure, affordable and low-carbon electricity supply during ‘dunkelflaute’ events – periods of low wind and solar energy generation. It builds on our recent briefing paper, ‘Filling the policy gap for long-duration energy storage: strategic reserves and market mechanisms’, also developed with University College London, on the growing role of long-duration energy storage (LDES) in Britain’s electricity system and the policy options to support it.
The UK’s transition to an electricity system based on variable wind and solar power, combined with the electrification of the economy, is increasing the challenge and importance of maintaining electricity system resilience.
Modelling indicates that prolonged shortfalls between electricity supply and demand – arising from a combination of low renewable generation, higher electricity demand, and available flexibility, influenced by weather conditions – are likely to occur in future and should be prepared for.
Dunkelflaute risk is best handled with a diversity of approaches, including LDES, low-carbon dispatchable generation, demand-side flexibility, interconnection and geographically diverse renewable deployment. However, current investment frameworks are not sufficient to secure adequate flexibility by employing a portfolio of solutions. Furthermore, the long development timelines for LDES, low-carbon flexibility and interconnectors add urgency, as infrastructure decisions taken today will determine resilience in the 2030s and beyond.
The submission highlights that a strategic reserve model should be considered for seasonal LDES and other low-carbon flexibility assets that can provide supply back-up during low-probability but high-impact extended dunkelflaute events. Strategic electricity storage should be recognised as the future equivalent of today’s oil and gas stocks and be planned for accordingly.
