Cloud cover helps offshore wind farms

Anyone calculating how much electricity an offshore wind farm will deliver looks at the wind and not at the clouds. Researchers at the University of Twente show that this leaves part of the yield unaccounted for. Low cloud cover speeds up the recovery of the wind behind a wind farm and can benefit the next farm in line. The research is on the cover of the scientific journal PRX Energy today.

Wind turbines take energy from the wind, so the air behind them moves more slowly. Behind an entire wind farm, this strip of slow air stretches for tens of kilometres across the sea. The wind only regains its strength once that slow air mixes with the faster air above it.

A cooling element on the ceiling

But there is more to the weather above a wind farm than wind. “Whether it’s a cloudy day or a clear sky doesn’t just matter for solar panels. It also affects how quickly the wind gets back up to speed,” says Richard Stevens, one of the researchers. The tops of the clouds radiate heat into space and cool down. Cooled air is heavier and sinks, and that stirs up the entire layer of air below it, all the way down to the height of the blades. As a result, the wind behind the farm regains its strength more quickly.

Stevens and postdoctoral researcher Davide Selvatici simulated a stretch of North Sea atmosphere with a cloud deck above it, then took it apart step by step. First they switched off the radiation, which removed the cooling at the top of the clouds. Then they also took the water out of the clouds, leaving a clear sky. Any mixing that disappeared between those three versions was therefore down to the clouds.

More and more farms in each other’s wind shadow

In the North Sea, wind farms are being built ever closer together. The wake of one farm, the strip of slow air behind it, reaches into the area of the next. How much yield that costs is calculated in advance with models that include the wind but leave out the cloud cover. Under a closed cloud deck, the wake recovers faster and the farm behind it can benefit. Over the North Sea, low cloud is the rule rather than the exception. Anyone who leaves the clouds out of the calculation will therefore systematically misjudge the yield of a farm that lies downwind of another.

The research is based on calculations, not on measurements at sea. That clouds behave this way is known from meteorology, and aircraft measurements have shown that wind farms affect each other. This is the first time the two have been calculated together, and the result still needs to be confirmed at sea. That requires measurements at turbine height under varying cloud cover.

About the research

The article Low-Level Cloud Radiative Forcing Enhances Wind-Farm Wake Recovery by Davide Selvatici and Richard Stevens was published in PRX Energy on 2 September 2026. The journal selected it as Featured in Physics, after which the American Physical Society’s Physics Magazine published a summary of the work. The research is part of the ERC project WINDFLOW and was carried out in the Physics of Fluids group.

DOI: 10.1103/86lm-1nr3