Spinning wind turbines spark clockwork lightning

The spinning blades of wind turbines don't just generate useful electricity. They also trigger bolts of lightning.

Little is known about these spontaneous bolts because turbines are hard to monitor in stormy conditions. But now Joan Montanyà of the Polytechnic University of Catalonia in Barcelona, Spain, and his colleagues have captured the first high-speed video of wind turbines firing lightning. They also used a lightning detection network to map how the bolts propagate in three dimensions.

The team found that, under certain atmospheric conditions, rotating turbine blades can produce a bolt each time one of the blades is at its highest position. Strikes often propagate up to 2 kilometres upwards.

Unexpectedly, the video revealed three turbines close together producing lightning at the same time. "It's surprising to see so much activity from turbines in a small area," says Montanyà.

Struck through the blade

Famously, in 2011 a UK wind turbine exploded in high winds that forced the blades to move against their brakes, generating enough friction to turn it into a fireball. But turbines are more vulnerable to lightning.

The frequent lightning bolts could be damaging turbine blades, which are made of carbon-reinforced plastic. They are designed to resist occasional electrical discharges, but regular bolts could degrade them faster. "Wind turbines are exposed to a lot of electrical discharges and can easily be stressed," says Montanyà.

Aircraft are also often struck by lightning. But they are better protected than turbines – their aluminium fuselage conducts electricity around them. This is not an option for turbine blades because the extra weight would reduce their efficiency.

Another reason that lightning bolts pose a bigger problem for wind turbines is that they are hard to inspect and repair. Their blades sit on a tall structure, making them difficult to access. By contrast, when an aircraft is struck by lightning, it is checked and repaired the next time it lands.

Montanyà hopes to find ways to cut the number of lightning bolts generated by turbines. The challenge is to find out why they happen so often. He suspects the spinning tip of the blade becomes charged through friction with the air. "Many YouTube videos have documented spark-ups from turbines but the effect responsible needs to be confirmed," says Montanyà.