Wind energy is one of the largest contributors to renewable energy generation, where the recent demand has led to growth in use as well as in physical size. Simply put, wind turbines are getting taller and capturing wind through a larger blade swept area.
Wind turbines are now more prone to lightning strikes due to the fact of their increased structural height.
There are approximately 2,000 thunderstorms at any given minute worldwide. This creates a great risk for tall structures, such as wind turbines, to be struck by lightning. The average electric current from a lightning return stroke is 30kA. This massive ﬂow of current can heat up the leader channel air to between 25,000C and 30,000C.
A lightning protection system (LPS) is composed of a lightning receptor, down conductor, and grounding. All elements must be well connected to pass the lightning current to earth safely. Although wind turbines are installed with LPS, there are still cases where blades and whole turbines are destroyed by lightning strikes. Considering the 20- to 25-year design life of wind turbines, it is important to safeguard them from lightning strikes, because the damage associated with it will cause the downtime of the turbine operation, causing extra costs for maintenance and a shortage of electricity.
The highest percentage of damages occur on the control system. Meanwhile, the damage caused to the blades is 11% of the time and it often corresponds with severe damage. The damages associated with lightning are blade rupturing and burnout, wire melting, surface cracking and delamination, lightning receptor vaporization, and loss. In most cases, the problem is somewhere between the last receptor and the root of the blade. The most common situation would be a broken wire or some issue within the lightning register box.
A single accident almost never means the halt of just one single turbine. Some incidents lead to a wind park of 40+ turbines being halted which means huge costs to the wind turbine company.
To avoid this, LPS needs to be checked at least once in 2 to 3 years.
A German study shows that 80% of insurance claims are caused by lightning. Other data has shown the rise of wind turbine yearly insurance fees - and it is expected to continue the same pattern and take an even bigger share on the balance sheet for the wind turbine owners. In some countries, insurers started to limit the scope of insurance coverage, because of additional challenges and the fact that one sole loss could wipe out an insurer’s entire premium pool for a single project.
So how can it be avoided?
Aerones can help to avoid costly damages by choosing planned inspections. Aerones have tested more than 2,600 blades and approximately 30% have problems with their lightning protection systems.
By using a robotized blade care system, it is much cheaper to identify and fix small damage on a lightning protection system than allocate resources after serious damages.
We need only 10 min to inspect one blade. A full LPS inspection takes less than 2 to 3 hours including the setup and the dismantling of the robotic system. That is faster compared to the traditional rope access technique which is also a lot riskier considering that the technicians are working in dangerous heights.
Aerones uses long wires to complete a full circuit test in order to check whether, in case of a lightning strike, the charge will be properly grounded.
Performing the full circuit test also allows finding where the wind turbine LPS system has missing connections, i.e., between the hub and the nacelle, the tower, and so on.
By using robotized systems, we can take care of the blades by inspecting, cleaning, and repairing. That way we increase the efficiency of the wind turbine, reduce downtime and idle stay, and also help save the maintenance costs significantly.