Dunkelflaute: what it means and why it matters

Dunkelflaute, a German term, refers to a phenomenon where there is a prolonged period of low wind and not much sunlight. While that sounds like a temporary inconvenience, it has far-reaching consequences for our energy systems and the environment.

Read on as we explore the meaning of dunkelflaute, why it matters for our green energy future, and potential solutions.

What is dunkelflaute?

Dunkelflaute is a German term that roughly translates to a "dark wind lull" or "dark doldrums". It describes a situation where there's minimal sunshine and wind for extended periods - meteorologists also refer to this as anticyclonic gloom.

This phenomenon is a significant concern for energy systems that heavily depend on renewables like wind and solar power, as it means using alternative energy sources to keep the electricity flowing.

In northern Europe, dunkelflaute is a fairly common occurrence during the dark winter months. However, countries like Japan can experience these events during both the summer and winter.

What causes dunkelflaute events to happen?

Dunkelflaute events are caused by specific meteorological conditions, which can vary for each country, but they usually happen when there's a static high-pressure system that causes a weaker than normal wind combined with overcast and cloudy weather.

Renewable electricity generation significantly declines during these periods because of the absence of wind and sunlight.

Why is dunkelflaute a problem?

Dunkelflaute is a problem for countries heavily reliant on renewable energy sources like wind and solar power. During these periods of low wind and sunlight, renewable electricity generation significantly decreases, creating a gap in the power supply.

To fill this gap and maintain a stable electricity supply, countries often have to resort to using more gas-generated and coal-generated electricity. But using fossil fuels for electricity not only costs more, but also makes it dirtier, leading to higher carbon emissions.

This reliance on fossil fuels during dunkelflaute events clashes with the global goals of transitioning to cleaner, renewable energy sources and achieving carbon neutrality.

How often do dunkelflaute events happen?

In the north of Europe (which, of course, includes the UK), dunkelflaute events are fairly common.

There can be anywhere from two to 10 dunkelflaute events a year, or between 50 and 150 hours on average per month during the peak winter months of November, December, and January. And each event can last from a few hours to a couple of days.

In the UK, where wind power made up 29.4% of the electricity mix in 2023, dunkelflaute events can cause this proportion to drop significantly. During a dunkelflaute event in December 2022, the UK grid’s peak power demand increased by 10% to 45GW, and the National Grid had to lean on gas-fired power plants to meet it.

How can the green energy revolution combat dunkelflaute?

Advancements in energy storage, grid management, and alternative zero carbon options are key aspects of the green energy revolution's response to the dunkelflaute challenge.

Let's explore these solutions in more detail.

1. Battery storage

Battery storage presents a promising solution to combat dunkelflaute by storing clean electricity generated in windy and bright times for use during low-wind and low-light conditions, ensuring a consistent power supply.

However, the UK faces challenges in rapidly expanding its battery storage capacity mostly due to manual processes. So while the technology has advanced significantly, the setup and operational costs remain high.

The UK's current grid infrastructure isn't set up for a sudden surge in battery storage systems, and new grid connection applications are facing wait times of up to 13 years.

2. Pumped storage

Pumped storage power plants function by absorbing peak electricity loads and using surplus power to pump water uphill into storage. During a dunkelflaute event, the stored water can be released quickly downhill, and this kinetic energy is used to generate electricity.

The plant’s ability to store large amounts of energy and release it on-demand makes it a dependable way of ensuring a steady power supply even during challenging weather conditions. The main downside is finding the space (and money) to construct pumped storage facilities.

3. Nuclear power

As a continuous and reliable energy source, nuclear power can provide power during periods of low light and wind.

While it isn't technically renewable, nuclear power is low-carbon and has a virtually limitless fuel supply, making it a potential ally in the green energy revolution. However, it does come with its own risks.

Potential catastrophic accidents, radioactive waste disposal, and weaponisation risks are serious issues that need careful attention and strong safety measures.

4. Demand-side flexibility

Demand-side flexibility, also known as demand-side management, involves various programmes, policies, and technologies that help cut down on consumers' electricity usage at peak demand times.

This can be achieved through financial incentives like the National Grid ESO's Demand Flexibility Service, which encourages consumers to use less power during high-demand periods by providing cash or credits for each kilowatt-hour (kWh) saved.

During a dunkelflaute event, when renewable electricity generation is low, demand-side flexibility can help balance supply and demand, preventing power shortages.

5. Hydropower

During a dunkelflaute event, hydropower can help balance supply and demand by compensating for the reduced output from wind and solar resources. 

Unlike wind and solar, which depend on weather conditions, hydropower can generate electricity consistently. However, the increasing frequency of heatwaves can make a hydropower source vulnerable to droughts.

Summary

As we've seen, dunkelflaute has significant implications for the energy sector. But while the concept may seem daunting and concerning, it's not a new phenomenon and there are plenty of solutions available to mitigate its effects.

By diversifying energy sources and investing in storage technologies, the renewable energy industry can work towards creating a more reliable and sustainable energy system all year-round.

Dunkelflaute: FAQs

What is a day with no wind called?

In weather reports and forecasts, a day with no wind is typically referred to as a "calm" day to indicate a lack of wind movement. But as peaceful as that sounds, it can pose challenges for activities that rely on wind.

No wind means no power for wind turbines, so they can't produce electricity on days like these. Which means alternatives such as solar, hydro, or traditional oil and gas power plants are needed to maintain a stable electricity supply.

What can you do when there’s no wind or sun?

Without wind or sun, it's almost impossible to generate renewable electricity from wind turbines or solar panels. So we turn to options like hydropower, which uses flowing water to generate electricity, or traditional fossil fuel power plants.

Energy storage systems, such as batteries, can also be used to supply stored electricity from previous windy or bright days. This diversification makes sure there's always power, no matter the weather.