Renewables need flexible backup not baseload

In the renewable energy sector, a ''dunkelflaute'' (, ) is a period of time in which little or no energy can be generated with

wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ho ...

and

solar power Solar power is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Photovoltaic cells convert light into an electric current using the photovolta ...

, because there is neither wind nor sunlight. In

meteorology Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did no ...

, this is known as anticyclonic gloom.

Meteorology

Unlike a typical

anticyclone An anticyclone is a weather phenomenon defined as a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere as viewed from ...

, dunkelflaute are associated not with clear skies, but with very dense cloud cover (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 Mus ...

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 th ...

, and fog. there is no agreed quantitative definition of dunkelflaute. Li et al define it as wind and solar both below 20% of capacity during a particular 60 min period. High

albedo Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refl ...

of low-level stratocumulus clouds in particular – sometimes 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 to ...

height is just 400 meters – can reduce the solar irradiation by half. In the north of Europe, the dunkelflaute 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 t ...

weather with

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, dunkelflaute are seen in summer and winter. The former is caused by stationary fronts in early summer and autumn rainy season (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 renewables. 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. Events that last more than two days over most of Europe happen about 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 elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...

oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...

and

natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...

hydroelectricity Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined an ...

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 ...

and, less often, energy storage to prevent

power outage A power outage (also called a powercut, a power out, a power failure, a power blackout, a power loss, or a blackout) is the loss of the electrical power network supply to an end user. There are many causes of power failures in an electricity ...

s. Long-term solutions include designing electricity markets to incentivize clean flexible power. 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) or carbon capture and sequestration is the process of capturing carbon dioxide (CO2) before it enters the atmosphere, transporting it, and storing it (carbon sequestration) for centuries or millennia. Usually th ...

and the

hydrogen economy The hydrogen economy is using hydrogen to decarbonize economic sectors which are hard to electrify, essentially, the "hard-to-abate" sectors such as cement, steel, long-haul transport etc. In order to phase out fossil fuels and limit climate ch ...

as possible parts of the solution.

References

Sources

* {{cite journal , last1 = Li , first1 = Bowen , last2 = Basu , first2 = Sukanta , last3 = Watson , first3 = Simon J. , last4 = Russchenberg , first4 = Herman W. J. , title = A Brief Climatology of Dunkelflaute Events over and Surrounding the North and Baltic Sea Areas , journal = Energies , date = 11 October 2021 , volume = 14 , issue = 20 , page = 6508 , eissn = 1996-1073 , doi = 10.3390/en14206508 , pmid = , url = https://pure.tudelft.nl/ws/portalfiles/portal/100313934/energies_14_06508.pdf, doi-access = free Electric power generation Anticyclones

Meteorology

Renewable energy effects

See also

References

Sources