Long-duration electricity storage needs for coping with Dunkelflaute events in Europe

TL;DR

This study analyzes Europe's need for extensive long-duration electricity storage to address prolonged low wind and solar power periods, emphasizing the importance of storage and transmission in ensuring energy system resilience.

Contribution

It quantifies the scale of long-duration storage needed for Europe to handle extreme renewable droughts, highlighting the role of storage and interconnection in decarbonization.

Findings

Extreme droughts determine storage operation and investment.

A minimum of 351 TWh storage is needed for the worst-case scenario.

Fossil backup and nuclear power have limited effects on reducing storage needs.

Abstract

Coping with prolonged periods of low availability of wind and solar power, also referred to as variable renewable energy droughts or "Dunkelflaute", emerges as a key challenge for realizing decarbonized energy systems based on renewable energy. Here we investigate the role of long-duration electricity storage and geographical balancing through transmission in dealing with such events in Europe, combining a time series analysis of renewable availability with power sector modeling of 35 historical weather years. We find that extreme droughts define long-duration storage operation and investment. Assuming policy-relevant interconnection, the least-cost system in our model capable of coping with the most extreme event requires 351 terawatt hours long-duration storage capacity, corresponding to 7% of yearly European electricity demand. While nuclear power can partially reduce storage needs, the storage-mitigating effect of fossil backup plants in combination with carbon removal is limited. Policymakers and system planners should prepare for a rapid expansion of long-duration storage to safeguard the renewable energy transition in Europe.