In the
renewable energy sector, a dunkelflaute (German:[ˈdʊŋkəlˌflaʊtə]ⓘ,
lit.'dark doldrums' or 'dark wind lull', plural dunkelflauten)[1] is a period of time in which little or no energy can be generated with
wind and
solar power, because there is neither wind nor sunlight.[2][3][4] In
meteorology, this is known as anticyclonic gloom.[5]
Meteorology
Unlike a typical
anticyclone, dunkelflauten are associated not with clear skies, but with very dense
cloud cover (0.7–0.9), consisting of
stratus,
stratocumulus, and fog.[6] As of 2022[update] there is no agreed quantitative definition of dunkelflaute.[7] Li et al. define it as wind and solar both below 20% of
capacity during a particular 60-minute period.[8] High
albedo of low-level stratocumulus clouds in particular – sometimes the
cloud base height is just 400 meters – can reduce
solar irradiation by half.[6]
In the north of Europe, dunkelflauten originate from a static high-pressure system that causes an extremely weak wind combined with
overcast weather with
stratus or
stratocumulus clouds.[9] There are 2–10 dunkelflaute events per year.[10] 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.[11]
In Japan, on the other hand, dunkelflauten are seen in summer and winter. The former is caused by stationary fronts in early summer and autumn rainy seasons (called Baiu and Akisame, respectively),[12] while the latter is caused by arrivals of south-coast cyclones.[13]
Renewable energy effects
These periods are a big issue in energy infrastructure if a significant amount of electricity is generated by solar and wind power.[14][1][15]Dunkelflauten can occur simultaneously over a very large region, but are less correlated between geographically distant regions, so multi-national power grid schemes can be helpful.[16] Events that last more than two days over most of Europe happen about every five years.[17] To ensure power during such periods flexible energy sources may be used,
energy may be imported, and
demand may be adjusted.[18][19]
^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.
ISSN1040-6190.
S2CID218966955.