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In the
renewable energy Renewable energy (also called green energy) is energy made from renewable resource, renewable natural resources that are replenished on a human lifetime, human timescale. The most widely used renewable energy types are solar energy, wind pow ...
sector, a ''dunkelflaute'' (, , plural ''dunkelflauten'') is a period of time in which little or no energy can be generated with
wind Wind is the natural movement of atmosphere of Earth, air or other gases relative to a planetary surface, planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heatin ...
and
solar power Solar power, also known as solar electricity, is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Solar panels use the photovoltaic effect to c ...
, because there is neither wind nor sunlight. In
meteorology Meteorology is the scientific study of the Earth's atmosphere and short-term atmospheric phenomena (i.e. weather), with a focus on weather forecasting. It has applications in the military, aviation, energy production, transport, agricultur ...
, this is known as anticyclonic gloom.


Meteorology

Unlike a typical
anticyclone A high-pressure area, high, or anticyclone, is an area near the surface of a planet where the atmospheric pressure is greater than the pressure in the surrounding regions. Highs are middle-scale meteorological features that result from interpl ...
, ''dunkelflauten'' are associated not with clear skies, but with very dense
cloud cover Cloud cover (also known as cloudiness, cloudage, or cloud amount) refers to the fraction of the sky obscured by clouds on average when observed from a particular location. Okta is the usual unit for measurement of the cloud cover. The cloud c ...
(0.7–0.9), consisting of
stratus Stratus may refer to: Weather *Stratus cloud, a cloud type **Nimbostratus cloud, a cloud type **Stratocumulus cloud, a cloud type **Altostratus cloud, a cloud type ** Altostratus undulatus cloud, a cloud type **Cirrostratus cloud, a cloud type Mu ...
,
stratocumulus A stratocumulus cloud, occasionally called a cumulostratus, belongs to a genus-type of clouds characterized by large dark, rounded masses, usually in groups, lines, or waves, the individual elements being larger than those in altocumulus, and the ...
, and fog. there is no agreed quantitative definition of ''dunkelflaute''. Li et al. define it as wind and solar both below 20% of
capacity Capacity or capacities may refer to: Mathematics, science, and engineering * Capacity of a container, closely related to the volume of the container * Capacity of a set, in Euclidean space, the total charge a set can hold while maintaining a giv ...
during a particular 60-minute period. High
albedo Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...
of low-level stratocumulus clouds in particularsometimes the
cloud base A cloud base (or the base of the cloud) is the lowest altitude of the visible portion of a cloud. It is traditionally expressed either in metres or feet above mean sea level or above a planetary surface, or as the pressure level corresponding t ...
height is just 400 meterscan reduce
solar irradiation Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre (W ...
by half. In the north of Europe, ''dunkelflauten'' originate from a static high-pressure system that causes an extremely weak wind combined with
overcast Overcast or overcast weather, as defined by the World Meteorological Organization, is the meteorological condition of clouds obscuring at least 95% of the sky. However, the total cloud cover must not be entirely due to obscuring phenomena near ...
weather with
stratus Stratus may refer to: Weather *Stratus cloud, a cloud type **Nimbostratus cloud, a cloud type **Stratocumulus cloud, a cloud type **Altostratus cloud, a cloud type ** Altostratus undulatus cloud, a cloud type **Cirrostratus cloud, a cloud type Mu ...
or
stratocumulus A stratocumulus cloud, occasionally called a cumulostratus, belongs to a genus-type of clouds characterized by large dark, rounded masses, usually in groups, lines, or waves, the individual elements being larger than those in altocumulus, and the ...
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), while the latter is caused by arrivals of south-coast cyclones.


Renewable energy effects

These periods are a big issue in energy infrastructure if a significant amount of electricity is generated by
variable renewable energy Variable renewable energy (VRE) or intermittent renewable energy sources (IRES) are renewable energy sources that are not dispatchable due to their fluctuating nature, such as wind power and solar power, as opposed to controllable renewable ener ...
(VRE) sources, mainly solar and wind power. ''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. 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, energy may be imported, and demand may be adjusted. For alternative energy sources, countries use fossil fuels (
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...
,
oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) and lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturate ...
and
natural gas Natural gas (also fossil gas, methane gas, and gas) is a naturally occurring compound of gaseous hydrocarbons, primarily methane (95%), small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium ...
),
hydroelectricity Hydroelectricity, or hydroelectric power, is Electricity generation, electricity generated from hydropower (water power). Hydropower supplies 15% of the world's electricity, almost 4,210 TWh in 2023, which is more than all other Renewable energ ...
or
nuclear power Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced by ...
and, less often,
energy storage Energy storage is the capture of energy produced at one time for use at a later time to reduce imbalances between energy demand and energy production. A device that stores energy is generally called an Accumulator (energy), accumulator or Batte ...
to prevent
power outage A power outage, also called a blackout, a power failure, a power blackout, a power loss, a power cut, or a power out is the complete loss of the electrical power network supply to an end user. There are many causes of power failures in an el ...
s. Long-term solutions include designing
electricity markets Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...
to incentivise clean power which is available when needed. 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 Carbon capture and storage (CCS) is a process by which carbon dioxide (CO2) from industrial installations is separated before it is released into the atmosphere, then transported to a long-term storage location.IPCC, 2021Annex VII: Glossary at ...
and the
hydrogen economy The hydrogen economy is an umbrella term for the roles hydrogen can play alongside low-carbon electricity to reduce emissions of greenhouse gases. The aim is to reduce emissions where cheaper and more energy-efficient clean solutions are not ava ...
as possible parts of the solution.


Droughts

By analogy with hydrological
drought A drought is a period of drier-than-normal conditions.Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D.  Jiang, A.  Khan, W.  Pokam Mba, D.  Rosenfeld, J. Tierney, ...
s, long used in planning for
hydroelectricity Hydroelectricity, or hydroelectric power, is Electricity generation, electricity generated from hydropower (water power). Hydropower supplies 15% of the world's electricity, almost 4,210 TWh in 2023, which is more than all other Renewable energ ...
, 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 Resource adequacy (RA, also supply adequacy) in the field of electric power is the ability of the electric grid to satisfy the end-user power demand at any time (typically an issue at the peak demand). RA is a component of the electrical grid relia ...
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 TWH or twh could refer to: * Tai Dón language, a language of Vietnam, Laos, and China * Tai Wo Hau station, Hong Kong; MTR station code * Tennessee Walking Horse, a breed of horse * Toronto Western Hospital, a hospital in Toronto, Canada * Tun ...
(on top of current projections) to accommodate a series of events of this magnitude.


See also

*
Duck curve The duck curve is a graph of power production over the course of a day that shows the timing imbalance between peak demand and solar power generation. The graph resembles a sitting duck, and thus the term was created. Used in utility-scale elect ...
*
Variable renewable energy Variable renewable energy (VRE) or intermittent renewable energy sources (IRES) are renewable energy sources that are not dispatchable due to their fluctuating nature, such as wind power and solar power, as opposed to controllable renewable ener ...


References


Sources

* * * * * {{cite report, last1=Somani, first1=Abhishek , last2=Barrett, first2=Emily, last3=Zhou, first3=Zhi, last4=Chan , first4=Gavin, last5=Middleton, first5=Luke, last6=Tarel, first6=Guillaume, last7=Campbell , first7=Allison, last8=Botterud, first8=Audun , last9=Bhatnagar, first9=Dhruv, last10=Beckitt, first10=Alex, last11=O'Reilley, first11=Christopher, last12=Zhu, first12=Yanyan, last13=Sun, first13=Xueqing, title=An Assessment of Resource Drought Events as Indicators for Long-Duration Energy Storage Needs, date=2024-05-01, doi=10.2172/2349123, doi-access=free, osti=2349123 Electric power generation Anticyclones