Dunkelflaute

English: Dark doldrums / German: Dunkelflaute / Spanish: Calma oscura / Portuguese: Calmaria escura / French: Calme sombre / Italian: Calma scura

Dunkelflaute in the environmental context refers to a meteorological weather condition where there is simultaneously little to no wind (wind lull) and low solar radiation (darkness) over an extended period. This phenomenon poses a central challenge for energy systems heavily reliant on renewable energy sources like wind power and photovoltaics, as it leads to a significant reduction in electricity generation from these sources.

General Description

The term "Dunkelflaute" is a compound word that combines the two crucial factors for electricity generation from wind and sun: the absence of wind and the absence of sunlight. Such periods typically occur during winter months when days are shorter and the sun is lower, and high-pressure systems simultaneously lead to calm weather conditions. A Dunkelflaute can last for several days and challenges an energy system with a high penetration of fluctuating renewable energies to secure power supply through other means.

Key characteristics of a Dunkelflaute are:

• Low Wind Energy Generation: Wind turbines stand still or produce only a fraction of their rated capacity due to insufficient wind.

• Low Photovoltaic Generation: Due to darkness (night), heavy cloud cover, or fog, solar panels produce little to no electricity.

• Simultaneous Occurrence: The critical element is the synchronous occurrence of both conditions, which drastically reduces the overall availability of renewable energies.

• Duration: Dunkelflauten can range from a few hours to several days.

• Seasonality: They occur more frequently in winter months when electricity demand for heating and lighting is simultaneously high.

Special Applications and Role in the Environmental Context

Dunkelflaute is a key factor in the debate surrounding the energy transition and security of supply with 100% renewable energies:

• Challenge for Grid Stability: During a Dunkelflaute, the missing electricity generation from wind and sun must be compensated by other sources to ensure grid stability and prevent blackouts.

• Need for Backup Capacities: This requires the use of dispatchable power plants (e.g., gas-fired power plants, biomass power plants) or energy storage systems that can be ramped up quickly.

• Storage Technologies: The development and expansion of long-term electricity storage (e.g., hydrogen storage, pumped-hydro storage, large-scale batteries) are central solutions to store surplus electricity from windy and sunny periods for Dunkelflauten.

• Sector Coupling: The linking of electricity, heat, and transport sectors can help to smooth out peak loads and increase the flexibility of the system, for example, through power-to-heat applications.

• Grid Expansion and European Interconnection: A high-capacity power grid and interconnection with neighboring countries enable the import of electricity from regions where wind is blowing or the sun is shining.

• Demand-Side Flexibility (Demand-Side Management): Incentives for consumers to reduce their electricity consumption during Dunkelflaute periods or shift it to times of high generation.

Areas of Application

The concept of Dunkelflaute is relevant in the following areas:

• Energy Industry and Policy: In the planning and design of future energy systems and the setting of expansion targets for renewable energies.

• Grid Operators: For ensuring grid stability and planning backup capacities.

• Research and Development: In the exploration of new storage technologies, smart grids, and sector coupling.

• Climate Protection and Sustainability: As a problem to be solved on the path to a fully CO₂-neutral energy supply.

What Needs to Be Done in Europe

To overcome the challenges of Dunkelflaute in Europe and advance the energy transition, several measures at the European level are crucial:

• European Electricity Market and Grid Expansion: A high-capacity and well-interconnected European electricity grid is essential. It enables cross-border electricity trading, allowing countries with surpluses of renewable energy (e.g., strong winds in Denmark or hydropower in Scandinavia) to supply other countries during a Dunkelflaute. The expansion of cross-border power lines is therefore of great importance.

• Diversification of Energy Sources: In addition to wind and solar energy, other dispatchable renewable energy sources such as biomass, geothermal, and hydropower should be expanded in Europe to reduce dependence on weather-dependent sources.

• Expansion of Storage Technologies: Europe must invest massively in long-term electricity storage. This includes hydrogen storage (power-to-gas technologies), pumped-hydro storage, and large-scale battery storage to store surplus electricity from periods of high generation for Dunkelflaute phases.

• Flexible Backup Solutions: Even if the goal is a complete supply from renewable energies, flexible backup power plants will be needed during transition phases and to bridge Dunkelflauten. The focus here should be on hydrogen-ready gas-fired power plants that can be operated with green hydrogen in the future.

• Research and Development: Continuous research in Europe is necessary to develop innovative solutions for the energy system, including improved forecasting models for wind and solar yields, smart grid control, and new storage technologies.

• Demand-Side Flexibility: The promotion of demand-side management and variable electricity tariffs across Europe can help to shift electricity consumption to times of high generation and reduce it during Dunkelflaute periods.

• Harmonization and Coordination: Closer coordination and harmonization of energy policy and grid expansion among European member states are essential to build a stable and resilient energy system.

These measures contribute to ensuring security of supply in Europe and successfully managing the transition to a sustainable and CO₂-neutral energy supply despite challenges like the Dunkelflaute.

Known Examples

• Winter Months in Central Europe: Germany and other countries in Central Europe regularly experience phases of Dunkelflaute, particularly from November to February.

• Historical Events: In the past, there have been several multi-day Dunkelflauten that led to high electricity prices on the exchange and an increased need for conventional power generation.

• Research Projects: Numerous research projects in Germany and Europe focus on modeling Dunkelflauten and developing solutions to overcome this challenge.

Risks and Challenges

Dunkelflaute presents the energy system with the following risks and challenges:

• Security of Supply: The main problem is the potential risk of electricity shortages or blackouts if there are insufficient backup capacities or storage.

• Costs: The operation of backup power plants (often gas-fired power plants) or the import of electricity during a Dunkelflaute can lead to significant cost increases.

• CO₂ Emissions: If Dunkelflauten have to be compensated by fossil fuel power plants, this leads to increased CO₂ emissions, which contradicts the goals of the energy transition.

• Dependence on Imports: A high dependence on electricity imports during Dunkelflauten can impair energy sovereignty.

• Planning Certainty: The irregular nature of Dunkelflauten complicates the precise planning and sizing of backup systems.

Example Sentences

• To bridge the Dunkelflaute, we need to make massive investments in energy storage.

• The Dunkelflaute is one of the biggest challenges for the complete transition to renewable energies.

• During the last Dunkelflaute, electricity prices on the exchange rose sharply.

• Research projects focus on forecasting and managing Dunkelflauten in the future energy system.

• The expansion of dispatchable biomass power plants can help to close the gaps during a Dunkelflaute.

Similar Terms

• Wind lull: A period with low wind speed.

• Residual load: The remaining load in the power grid that cannot be covered by fluctuating renewable energies.

• Security of supply: Ensuring a reliable and uninterrupted energy supply.

• Energy storage: Technologies for storing energy to release it when needed.

• Sector coupling: The integration of various energy consumption sectors (electricity, heat, transport) to increase system flexibility.

• Blackout: A widespread and prolonged power outage.

Summary

Dunkelflaute in the environmental context describes a weather condition where there is simultaneously little wind and low solar radiation, which significantly reduces electricity generation from wind power and photovoltaics. It is a central challenge for the energy transition, as it increases the need for backup capacities and storage solutions to ensure security of supply and enable the transition to a fully renewable energy system.

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