As long ago as 1995, a German study reported that more than 80% of insurance claims for damage to wind turbines were paid as result of lightning strikes. A little thought will reveal that this is not particularly surprising. Wind turbines are tall structures and their blades have a small radius of curvature at their tips, which encourages the build up of electrical charge and, therefore, increases their vulnerability to lightning.
At the time the study was carried out, the largest wind turbines had a generating capacity of around 150 kW. The corresponding figure today is 6 MW. This increase in generating capacity has necessarily been paralleled by an increase in the physical size of the turbines – whereas 60 m high was once the norm, heights in excess of 160 m are now common, and even taller structures are not unknown.
The risk of wind turbines suffering lightning strikes today is, therefore, even greater than it was in 1995. And, in fact, that risk is in many cases further increased by the locations that are typically favoured for the siting of wind turbines. These include open land, coastal regions, mountain ridges and offshore, all of which mean that the turbines are likely to be the highest structure in the area.
And lightning strikes are extremely damaging to wind turbines. A direct strike on an unprotected blade will increase its temperature by tens of thousands of degrees almost instantaneously. Since the blades are hollow, this heating means that the air within the blade expands with explosive force, often virtually destroying the blade, and always making it unfit for further service. For anyone who wants to see the results with their own eyes, there are several dramatic videos currently available on YouTube.
Less energetic or indirect strikes may not cause such obvious damage to the blades, but they can create hidden problems that greatly shorten blade service life. In addition, wind turbines invariably incorporate electronic subsystems that are vulnerable to damage from lightning strikes and the resulting voltage surges.