A small ‘dunkelflaute’ hanging over Belgium is causing electricity prices to spike. The term ‘dunkelflaute’, a combination of the German words ‘dunkel’, meaning ‘dark’, and ‘Flaute’, meaning ‘lull’, describes the simultaneous occurrence of darkness and a lull in wind activity. Dunkelflautes occur several times every winter in Northwestern Europe. They usually last 1–3 days.

The phenomenon is due to expected gray and windless weather, which results in very little renewable energy being produced. When renewable production drops, the electricity system must rely on gas-fired power plants and imports, which are more expensive.

Marginal prices

These sources often set the marginal price on the wholesale market. Yesterday, on the wholesale electricity market, up to 135 euros had to be paid per megawatt-hour to receive electricity today.

Belgium covers dunkelflautes using gas-fired power plants, imports, strategic reserve capacity, and temporary demand reduction by large consumers. Dunkelflautes are a stress test for a renewable-based system. They underline the importance of energy storage, flexible demand, and better geographical spread of renewables.

Even in summer, such a gray and windless day can occur. Running air conditioners as soon as the sun disappears can then lead to higher electricity prices. Instead of a ‘dunkelflaute’ (dark blue), we then call it a ‘hitzeflaute.’