(Updated April 2026) The so-called Dark doldrums is considered one of the greatest challenges of the energy transition. It describes a weather situation in which at the same time there is hardly any wind and little solar energy is available – exactly when renewable energies supply very limited electricity. So it is the exact opposite of a Hellbrunn.
But how critical is the "dunkelflaute" really – and what solutions are there?
What is a dark doldrum?
A dark doldrum is a period in which:
- when little wind energy is generated (calm)
- when little or no solar energy is available (e.g., at night or during heavy cloud cover)
Sequence: Electricity generation from wind and PV systems can less than 2 % of installed capacity sink.
These situations are typical, especially in winter, and they can several days to over a week.
Is there an official definition?
No, a single definition does not exist.
Depending on how you look at it:
- frequent short eventsseveral times a year
- longer critical phases (> 1 week)about every 5–10 years
For the energy industry, especially multi-day periods of darkness with high load relevant.
Why is the Dunkelflaute a problem?
1. Supply gap in the electricity system
When wind and solar power fail simultaneously:
- is the demand for Backup capacities
- electricity in the short term imported or conventionally generated become
2. High electricity prices
Shortage leads to:
- rising stock market electricity prices
- higher costs for businesses
3. CO₂ emissions rise in the short term
Without sufficient alternatives:
- Deployment of Gas or coal power plants
- Goal conflict for climate neutrality
4. Grid Stability Under Pressure
- Higher demands on network management and reserve power
- Frequency holding becomes more difficult
What is a „cold dark doldrums“?
A particularly critical form is the cold doldrums:
- usually occurs in winter
- combined low power generation with high consumption
- e.g. through heating demand and industrial production
This situation places the energy system under maximum strain.
How can the dark doldrums be solved?
The good news: There is no single solution, but an effective mix of measures.
1. Grid Expansion & European Networking
- Expansion of High-voltage direct current (HVDC)
- Long-distance power transmission
- Balancing regional weather differences
Example: Wind power from Northern Europe compensates for calms in Central Europe.
2. Energy storage as a key technology
Short-term memory:
- Battery Energy Storage System (BESS)
- Ideal for hours to days
Long-term storage:
- Pumped storage power plants
- Gravity storage and compressed air caverns
- Hydrogen (Power-to-Gas)
Goal: Store surpluses and retrieve them during dark doldrums
3. Flexible Backup Power Plants
Current: Flexible Gas power plants
perspectival
- Hydrogen power plants
- Biomass
- Geothermal
Important: quickly adjustable power
4. Sector Coupling
Sector coupling is the connection of:
- Strom
- Heat
- Mobility
Examples:
- Control heat pumps flexibly
- Targeted charging of e-cars
Energy is optimized across systems
5. Flexible electricity demand
Companies can actively contribute:
- Load shifting Demand-Side Management
- Use of dynamic electricity tariffs
- Adaptation of production times
Power consumption follows generation – not the other way around
6. Decentralized Energy Supply
- Commercial roof solar power systems
- On-site battery storage
- Combination with Energy management systems (EMS)
This reduces network dependency and stabilizes the overall system.
7. Hydrogen as a long-term storage
Centrally in the long term:
- Storage of large amounts of energy
- Use of existing gas infrastructure
- Power generation on demand
Potential: Secure supply for weeks or months
What role do companies play in dark doldrums?
Companies are a crucial part of the solution:
- Self-sufficiency with PV + Storage
- Participation in Flexibility markets
- Peak load reduction
- Integration in intelligent energy systems
Result:
- Contribution to grid stability
- lower electricity costs
- higher security of supply
Conclusion: Dunkelflaute is solvable – but only systemically
The dark doldrums are not an insurmountable hurdle, but a plannable challenge.
A stable energy system of the future is based on:
- renewable energies
- Save
- flexible consumers
- intelligent grid infrastructure
The interplay of all components is crucial.
For companies, this means that those who invest in flexible energy supply today will secure economic advantages and reduce risks in an increasingly volatile energy market.
Frequently Asked Questions
What is a dark doldrum?
A "dunkelflaute" (dark calm) is a weather condition characterized by very little wind and low solar energy availability simultaneously. This causes a significant drop in electricity generation from renewable sources.
How often does a period of low wind occur?
Short periods of darkness occur several times a year. Longer, critical phases with very low electricity generation lasting several days occur on average every 5 to 10 years.
How long does a period of darkness or low sunlight last?
The duration can vary greatly:
- extended periods of darkness: up to 7-10 days or more
- Short-term events: 1–3 days
Dunkelflaute is problematic because it refers to a period of low wind and low solar irradiation, meaning that both wind turbines and solar panels produce very little electricity. This can be a significant challenge for the energy supply, especially in regions that rely heavily on renewable energy sources like Germany.
During a period of low wind and solar power generation, electricity production from wind and solar power plants drops significantly. At the same time, electricity demand remains or even increases, leading to:
- higher electricity prices
- can lead to increased demand for backup power plants.
- rising CO₂ emissions
How can a period of low wind generation be overcome?
Several measures are combined to bridge the gap:
- Battery storage and pumped-storage hydroelectricity
- Hydrogen as long-term storage
- Flexible gas power plants
- European power grids
- Load management and flexible consumers
What role do companies play in dark doldrums?
Companies can actively contribute to the solution through:
- Usage dynamic electricity tariffs
- Self-sufficiency with photovoltaics and battery storage
- Load shifting (Demand Side Management)
Will the Dunkelflaute halt the energy transition?
No. The Dunkelflaute is considered a solvable challenge. By expanding storage, grids, and flexible energy systems, supply security can be guaranteed even with renewable energies.