In the renewable energy sector, a dunkelflaute (, , plural dunkelflauten)
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 cloud, stratocumulus, and fog. there is no agreed quantitative definition of
dunkelflaute.
Li et al. define it as wind and solar both below 20% of
capacity factor during a particular 60-minute period.
High
albedo of low-level stratocumulus clouds in particularsometimes the
cloud base height is just 400 meterscan reduce solar irradiation by half.
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 cloud or stratocumulus clouds. There are 2–10 dunkelflaute events per year. 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.
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),
Renewable energy effects
These periods are a big issue in energy infrastructure if a significant amount of electricity is generated by variable renewable energy (VRE) sources, mainly solar and wind power.
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. Events that last more than two days over most of Europe happen about once every five years.
To ensure power during such periods flexible energy sources may be used,
Interconnector, and demand may be adjusted.
For alternative energy sources, countries use fossil fuels (coal, oil and methane gas), hydroelectricity or nuclear power and, less often, energy storage to prevent .
Droughts
By analogy with hydrological
, long used in planning for
hydroelectricity, the researchers of the future VRE-intensive power grids in the 2020s started using the term
variable renewable energy drought (
VRE drought or simply
power drought) that is nearly synonymous to the dunkelflaute. Unlike the dunkelflaute, the drought can be a series of isolated adverse events, the most severe effects are forecasted are of this series type, and the planning for resource adequacy thus should span multiple years. Kittel et al. indicate the years 1996–1997 as particularly bad example of the VRE drought, they call for an additional EU-wide energy storage of 50 to 170
TWh (on top of current projections) to accommodate a series of events of this magnitude.
See also
Sources
