# Dunkelflaute

Dunkelflaute (German: [ˈdʊŋkəlˌflaʊtə], lit.'dark doldrums' or 'dark wind lull',[1] known in meteorological literature as anticyclonic gloom[2]) is a term used in the renewable energy sector to describe a period of time in which little to no energy can be generated with the use of wind and solar power.[3][4][5]

A short dunkelflaute of one day on Tuesday on the right graph.

## Meteorology

Unlike a typical anticyclone, Dunkelflaute events are not associated with clear skies, but very dense cloud cover (0.7–0.9), consisting of stratus, stratocumulus, and fog[6] that last for more than one day.[citation needed] High albedo of low-level stratocumulus clouds in particular - sometimes the cloud base height is just 400 meters - can reduce the solar irradiation by half.[6]

In the North of Europe, the Dunkelflaute events originate from a static high-pressure system that causes an extremely weak wind combined with overcast weather with stratus or stratocumulus clouds.[7] There are 2–10 Dunkelflaute events per year.[8] Most of these events occur from October to February; typically 50 to 150 hours per year, a single event usually lasts up to 24 hours.[9] A year is 8760 hours, 50h/8760h=0.5%, 150h/8760h=1.5%.[citation needed]

## Renewable energy effects

These periods are a big issue in energy infrastructure if a significant amount of electricity is generated by renewables.[10][11] Dunkelflaute can occur simultaneously over a very large region, but is less correlated between geographically distant regions, so multi-national power grid schemes can be helpful.[12] To ensure power during such periods alternative energy sources must be present in a sufficient capacity, energy can be imported and demand can be adjusted.[13]

For alternative energy sources, countries use fossil fuels (coal, oil and natural gas), hydroelectricity or nuclear power and, less often, energy storage to prevent power outages.[14][15][16][17][18] A group of countries is following on from Mission Innovation to work together to solve the problem in a clean low-carbon way by 2030: including looking into carbon capture and storage and the hydrogen economy as possible parts of the solution.[19]

## References

1. ^ "When the wind goes, gas fills in the gap | Q1 2021 Quarterly Report | Electric Insights". 2021-05-24. Retrieved 2021-06-29.
2. ^ Li et al. 2021, p. 2.
3. ^ "Dark doldrums: When wind and sun take a break". Retrieved 2021-05-27.
4. ^ Matsuo, Yuhji; Endo, Seiya; Nagatomi, Yu; Shibata, Yoshiaki; Komiyama, Ryoichi; Fujii, Yasumasa (2020-06-01). "Investigating the economics of the power sector under high penetration of variable renewable energies". Applied Energy. 267: 113956. doi:10.1016/j.apenergy.2019.113956. ISSN 0306-2619. S2CID 216301290.
5. ^ Ohba, Masamichi; Kanno, Yuki; Nohara, Daisuke (2021-12-08). "Climatology of dark doldrums in Japan". Renewable and Sustainable Energy Reviews. 155: 111927. doi:10.1016/j.rser.2021.111927. S2CID 245067748.
6. ^ a b Li et al. 2021, p. 7.
7. ^ Li et al. 2021, p. 6.
8. ^ Li et al. 2021, p. 11.
9. ^ Li et al. 2021, p. 1.
10. ^ "What happens with German renewables in the dead of winter?". Deutsche Welle. Retrieved 2021-05-28.
11. ^ "When the wind goes, gas fills in the gap". 24 May 2021. Retrieved 2021-06-06.
12. ^ Li et al. 2021, p. 9.
13. ^ Modelling 2050: Electricity System Analysis (PDF) (Report). Department for Business, Energy and Industrial Strategy.`{{cite report}}`: CS1 maint: url-status (link)
14. ^ Kosowski, Kai; Diercks, Frank (2021). "Quo Vadis, Grid Stability?" (PDF). Atw. 66 (2): 16–26. ISSN 1431-5254.
15. ^ Ernst, Damien. "Big infrastructures for fighting climate change" (PDF). Université de Liège.
16. ^ Diermann, Ralph. "Energie: Wie riskant sind Dunkelflauten von Wind- und Solarenergie?". Süddeutsche.de (in German). Retrieved 2021-04-22.
17. ^ Li, Bowen; Basu, Sukanta; Watson, Simon J.; Russchenberg, Herman W. J. (2020). "Mesoscale modeling of a "Dunkelflaute" event". Wind Energy. 24 (1): 5–23. doi:10.1002/we.2554. ISSN 1095-4244.
18. ^ Abbott, Malcolm; Cohen, Bruce (2020). "Issues associated with the possible contribution of battery energy storage in ensuring a stable electricity system". The Electricity Journal. 33 (6): 106771. doi:10.1016/j.tej.2020.106771. ISSN 1040-6190. S2CID 218966955.
19. ^ "Major project aims to clear clean energy hurdle". BBC News. 2021-06-02. Retrieved 2021-06-03.