Measuring the Dunkelflaute: How (not) to Analyze Variable Renewable Energy Shortage

Abstract

As variable renewable energy sources increasingly gain importance in global energy systems, there is a growing interest in understanding periods of variable renewable energy shortage (``Dunkelflauten''). Defining, quantifying, and comparing such shortage events across different renewable generation technologies and locations presents a surprisingly intricate challenge. Various approaches exist in different bodies of literature, such as hydrology, wind and solar energy analysis, or energy system modeling. The subject of interest in previous analyses ranges from single technologies in specific locations to diverse technology portfolios across multiple regions, focusing either on supply from variable renewables or its mismatch with electricity demand. We provide an overview of methods for quantifying variable renewable energy shortage. We explain and critically discuss the merits and challenges of different approaches for defining and identifying shortage events and propose further methodological improvements for more accurate shortage determination. Additionally, we elaborate on comparability requirements for multi-technological and multi-regional energy shortage analysis. In doing so, we aim to contribute to unifying disparate methodologies, harmonizing terminologies, and providing guidance for future research.