Dunkelflaute events are extended periods when scarcity of variable renewable energy, low wind and low solar energy generation, occur. One of the challenges for power systems with high wind and solar shares is resource adequacy – to prepare for long duration scarcity of weather dependent energy generation. Solar and wind energy often have a beneficial anti-correlation, however, it is still possible that even balanced shares of wind and solar will result in several consecutive days of low resource. How long are these periods – for different threshold energy production as well as for different shares of wind and solar, is an important question. This will also depend on the local resources and thus it is relevant to study for different regions.

Task 25/63 of IEA Wind TCP, together with Task 9 or IEA Hydro TCP, have made a joint effort in outlining a method to combine wind and solar energy and calculate longer (several days) events from long term data of several decades. We use sliding averages of 24 hours, and identify the frequency of different length periods when energy generation is on average below a threshold (for example 10% of installed capacity). Wind and solar generation with different shares as of installed capacity will be combined - and one case of same wind and solar share will be included to enable comparisons.

In this paper and presentation, we show the analyses for different regions and conclude with a list of impacts dunkelflaute events have on resource adequacy of power and energy systems.