The wind industry is transitioning. Rotor diameters are increasing, carbon fiber blades are becoming more widespread, and engineers all over the world are constantly developing and adjusting turbine designs, stretching the boundaries of operation.

We are seeing these trends, but are we – in the entire supply chain – fully prepared for them?

Lightning protection for wind turbines

Wind turbines are highly exposed to lightning strikes. The frequency of these strikes and the downward vs upward lightning ratio depend on a variety of factors, including geographical location, local weather phenomena, surrounding environment, topography, terrain, and seasonal variations.

Designing and implementing reliable lightning protection solutions (LPS) is essential to lower operational and maintenance costs. But to design such a system, it is crucial to understand the correlation between lightning frequency and structure heights.

Correlation between number of strikes and structure height

The below graph shows the general correlation between the number of strikes (or lightning frequency) and structure height. The graph is based on IEC standard calculations, where we considered an average ground flash density of 2 strikes per year per km².

As depicted above, the number of downward strikes increases with the square of the structure height (i.e., from 0.6 strikes per year at 100m increasing to 5.1 strikes per year at 300m). For upwards strikes, however, we see an even more significant increase with an exponential correlation. This correlation means that the total number of strikes also increases dramatically with increasing structure heights.

Risks for today’s and tomorrow’s wind turbines

Today, the average height of onshore wind turbines is around 150m. But the next generation of onshore turbines have risen to >200m. This 50m increase in structure height will more than double the frequency of lightning hitting the turbines.

As for offshore turbines, the current average height is around 200m, but the next generation turbines have increased to a structure height of 280m. This will triple the frequency of lightning strikes affecting the turbines.

With the race towards bigger turbines, we are also transitioning towards using more carbon fiber blades. But carbon blades bring a whole other complexity to LPS.

Even more complex LPS for future carbon blades

When designing an LPS for carbon blades, engineers must carefully consider – amongst others - how far out to the tip can they place the carbon and what kind of down conductor should they use.

But looking at the graph above, we see another element of complexity: increasing lightning frequency with structure height. This will add another layer of complexity to designing LPS for carbon blades.

The problem is, however, that the LPS testing requirements remain the same – but the lightning exposure does not. The next generation of wind turbines is exposed to higher lightning risks, and this will directly influence WTG designers, park owners and insurance providers.

Considerations for the wind industry

As lightning exposure is increasing for larger turbines, there is an overall requirement for even more durable LPS for wind turbine blades. In addition to this, there is an increased value in implementing enhanced lightning monitoring and maintenance plans to ensure complete lightning protection while minimizing downtime and costs.

But we also need to acknowledge the increased lightning risks with taller turbines if the design is inherited from smaller turbines. It will no longer be sufficient to look at the testing requirements without considering the increase in lightning occurrence.

In the race towards installing bigger turbines and transitioning towards carbon blades, it will be more important than ever to look at LPS and risks holistically and to closely collaborate within the entire supply chain. Polytech will continue to remain your strategic partner, helping protect your assets with reliable LPS and monitoring systems.