This piece is by Ed Hillier, Associate Director, Natural Resources, Charles Taylor Adjusting and Morten E. Handberg, Chief Blade Specialist at Wind Power LAB, and it looks at wind turbines and the lightning strike risk associated with them.
Lightning is an ever-present, natural, and even necessary phenomenon. Indeed, the destructive power of a lightning strike, and the resulting wildfires it can cause, is actually key to the lifecycle of some species of flora.
The aviation industry has managed to adapt to the threat of lightning strikes as aircraft technology evolves. Despite the fact that most aircraft components now are excellent conductors of electricity due to their high aluminium content, there is often little damage when lightning does hit, which happens approximately every 1,000 to 3,000 flying hours, according to the Royal Canadian Airforce.
This is because sophisticated lightning protection systems incorporating numerous materials are now a key safety feature in all aircrafts. In short, it’s a well-researched and understood science.
Conversely, the Wind Turbine Generator industry paints a different picture. Despite Wind Turbine Generators (WTGs) being relatively unattractive as electrical conductors, the insurance market has experienced considerable losses as a result of damage caused by lightning strikes to WTGs, especially to the blades.
What’s the damage?
Damage to the blades of WTGs as a result of lightning strikes are varied in nature and cost. Most lightning strikes cause damage to the tip of the blade, requiring a minor structural repair taking 3-7 days.
However, lightning strikes affecting the structural parts of the blade or damaging large sections of the blade shell can require a large and complex repair procedure, usually with the blade having to be demounted and repaired on the ground. This is due to the complexity of the repair, but in many cases it’s to ensure that the blade does not change curvature during the repair. This can take anything between 2-4 weeks with a cost up to that of a new blade.
For a given windfarm each turbine should expect one lightning strike within its collection range each year. This comes with a large deviation based on geolocation, and will depend on lightning characteristics, blade design, Lightning Protection System (LPS) and blade degradation.
Why is this so?
The first point to consider is the construction of a WTG blade. These blades are essentially Fibre-Reinforced Plastic (FRP) shaped to form the desired aerofoil shape. Neither the glass fibers (GF) or resin are conductive materials, but the cured resin and the combined GFRP composite can create a static charge. Although when amalgamated to form a blade the structure is a less effective conductor than a comparable unit made from aluminium or carbon fibre.
The net result is that despite being relatively unattractive as an electrical conductor, their blades are still struck on a regular basis due to their elevation and the relative lack of taller, more conductive structures in the vicinity. If there was no Lightning Protection System (LPS) built into these blades, they would be unable to quickly dissipate the huge and sudden energy release caused by a lightning strike which would likely result in catastrophic damage.
Are Lightning Protection Systems keeping pace with the advancement of WTG technology?
Whilst all commercial LPS are designed around the standards as set out in IEC 61400-24 which was first published in 2002, an updated 2018 version addresses the lightning risk of the increasing size of WTGs and their associated technology. That said, anecdotal claims information tells us that there has been a steady increase in damaging lightning strikes to blades, indicating that the progress in LPS development may not be keeping pace with the development of increasingly larger WTGs.
This is something that the 2018 edition of IEC 61400-24 seeks to rectify. Given the increasing number of deployed WTG especially in the onshore market, that were designed before these new standards were adopted, the commercial reality of the cost of retrofitting these fleets versus their remaining operational life and income is a challenge many operators may need to consider in the coming years.
How can lightning events be monitored?
There are several ways to monitor lightning events. Broadly speaking, two different solutions exist. The first is through global lightning sensor networks that monitor lightning activity on a global scale. This is the type of sensor typical of weather forecasts. The second type are hardware sensors installed directly in the blade or in the turbine to monitor if a lightning surge has passed through the tower.
If one of these solutions is combined with lightning event monitoring it can be a strong tool to manage lightning risks and ensure prudent operation of the turbines.
An example of such a tool is Wind Power LAB (WPL) lightning surveillance service (LASSIE). Here the owner/operator will receive an alert and analysis on the lightning attachment and a recommendation for operation and inspection.
If there is a risk that lightning damage has occurred, an external drone is the most suitable option for detection as structural damage caused by lightning is not always visible through binoculars or ground based camera solutions.
So where does this leave the insurer who is facing an increasing number of lightning related losses?
The answer to this in terms of onshore WTG may not be a palatable one but will centre largely on the nature of the WTG generating assets they insure, their operational life, and the willingness or otherwise of the Insured to invest in preventative measures.
That said, there is only so much that can realistically be done to improve the LPS of an existing asset and so perhaps prudent risk selection and policy wordings can assist with a more equitable risk transfer. In contrast, in the offshore space where the majority of the technological advances are being made and the majority of larger capacity WTG units exist, damaging lightning strikes rarely seem to occur.
In summary, lightning has, is, and always will be a natural phenomenon that humanity and its engineers can best hope to mitigate rather than tame. Through increased knowledge will come resilience. In the meantime, insurers will be called upon to fill this gap with suitable risk transfer products and by working with all interested parties, a better-quality risk will result.
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