Dark doldrums occur when there is no wind and darkness simultaneously. Find out how common they are, what risks they pose and how they can be compensated.
Experts use the term “dark doldrums” to describe a weather constellation in which a dark sky and no wind coincide. In such situations, neither solar systems nor wind turbines can work optimally.
The coincidence of these two weather conditions has recently become a focus of research into the energy transition. The study aims to find innovative solutions for this weather-related Achilles heel of renewable energies. But do not worry about any energy shortcuts or being unable to play Hell Spin’s Real-Time Dealer Games anymore.
Dark doldrums: The definition is (still) unclear
Dark doldrums impair the production of electricity from solar and wind energy.
The term “dark doldrums” comes from the field of renewable energies. It refers to a prolonged period in which there is little or no sunshine and little or no wind. This impacts energy generation because the electricity yield from wind turbines and photovoltaics drops sharply due to such outages.
A dark doldrums can only last for a few hours, but in the worst case, it can last for days or weeks. It has yet to be clearly defined which threshold values must apply to speak of a dark doldrums.
Because wind energy depends on natural weather conditions, dark doldrums are unavoidable. The risk is exceptionally high in the fall and winter months. To prevent power outages despite prolonged periods of calm and darkness, it is essential that the power grid can compensate for such outages. For example, the grid can be backed up by stored energy reserves or electricity from other energy sources.
How often do dark doldrums occur?
The risk of dark doldrums is highest in late fall and winter. According to weather data from the German Weather Service:
The risk of dark doldrums increases in the late fall and winter when the days get shorter and darker. The German Weather Service (DWD) has analyzed exemplary weather data and calculates that dark doldrums can occur on average twice a year. The DWD’s analysis assessed the dark doldrums that affected large areas and lasted 48 hours or longer. According to a 2017 study, longer dark doldrums lasting two weeks occur on average every two years in Germany.
According to the Dunkelflauten-Guide:
The dark doldrums guide the Science Media Center Germany (SMC) developed provides more up-to-date data. Here, the electricity generation data from 2015 to 2021 can be analysed explicitly for more extended periods of calm. Various criteria can be set flexibly, for example, the minimum duration of the doldrums or the maximum share of solar and wind energy in the electricity mix at the relevant time. This proportion is a significant value, as the greater it is, the greater the load a dark doldrums places on the rest of the power grid. Users can thus adapt the guide to their individual research needs. This is helpful because, as mentioned, there are no official threshold values for dark doldrums and no universally valid definition, as the SMC notes.
In the guide, a maximum per cent of wind and solar energy of 30 per cent is set as the default value. The preset minimum duration of a lull is 168 hours (7 days). If all default values are adopted, this results in a list of a total of 13 events between 2015 and 2021 that can be considered a dark doldrums. This aligns with the DWD’s estimate that there are an average of two major dark doldrums annually. All events on the list occurred
between October and February.
The longest dark doldrums in the period under review began on January 15, 2017, and lasted 334 hours, or almost two weeks. The last dark doldrums on the list began on January 1, 2019, and lasted 187 hours, or just over seven days. However, the guide also makes it possible to record shorter events lasting a few hours, which occur much more frequently.
What do dark doldrums have to do with the energy transition?
The proportion of renewable energies in the electricity mix is steadily increasing in Germany: According to figures from the Federal Statistical Office, it was 56 percent in 2023. The target set for the energy transition is to increase this share to 80 percent by 2030. The electricity supply is, therefore, increasingly dependent on wind and solar energy.
Against this backdrop, dark doldrums are also becoming a more significant stress test: The more electricity is fed from renewable energies, the more electricity is missing when these energy sources fail over a more extended period. Such outages can be compensated for by reserves (more on this in the next paragraph). Nevertheless, innovative use of the available energy is required to secure the supply permanently. The SMC analyzed the available data to find future solutions to the problem of dark doldrums.
