Whereas carbon is produced in individual planks that are insulated from each other, making the design effort more complex. Carbon, however, has the electrical downside of conducting current, creating new challenges for turbine design.įor traditional glass fibre blades, a single down conductor is required, which is very easy to implement. The challenges increase as the structures get bigger and more complex, and of course, due to access issues, damage to offshore wind turbines is significantly more expensive to address than onshore.įurthermore, when blades get bigger and longer, they need to be lighter, for which carbon is an ideal material and now routinely used. This is because the turbine will need to be shut down and the damage repaired, which can involve heavy machinery such as cranes. When damage occurs, it can be extremely costly to fix, as the Vestas case study shows. Though turbines and their blades are designed to withstand a certain severity of lightning, this can sometimes be exceeded causing harm to the structure. Madsen says that around 70% of all the strikes measured in turbines are actually starting on the blade and triggered by the turbine. Modern structures can easily exceed 200m in tip height. The upwards lightning effect starts to happen when a turbine exceeds 100m in height. “Initially, in early discussions on the risk of lightning strikes to turbines, the latter was not understood, which led to an underestimation of how many events a turbine will actually experience because the risk assessment was based on the lightning environment before the turbine was erected,” explains Madsen. Two types of lightning can occur, he says: one that starts in a thunderstorm and then propagates downwards, attaching to the turbine tip – called downward initiated lightning – and another, ‘upward lighting’, that happens when the turbine gets very tall and itself starts to generate lightning that wouldn’t otherwise occur. Madsen, head of simulation and modelling at global lightning protection services company Polytech, has worked in the field of wind turbine lightning strikes for 15 years and says that, on average, a blade will receive around 20 strikes during its lifetime, but the number will largely depend on the geographical location of a wind farm. However, while experts can’t say with any certainty how much lightning damage is occurring across the industry, it is a well-known threat. Tall structures are attractive to lightning, especially when located in flat planes with nothing much else around, as wind turbines often are. What’s more, experts say that it’s a problem that is set to worsen as turbines get taller and blades are increasingly made of carbon. Vestas’s story highlights the hidden costs and challenges that lightning strikes can pose to the wind power sector.
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