Into the wind

If you can survive the weather in the Arctic Circle, the North and Baltic Sea climate won't bother you either. That was what the members of a materials science team thought when they went to test a robust paint for wind turbines. In Iceland.

Four wind turbines and a ship in stormy seas
© Ian Dyball/iStock

The coatings on wind turbines are regularly tested. Repairs can be expensive – especially on off-shore plants.

Wet winters, dry summers and extreme temperature fluctuations combined with the strong winds from a volcanic island full of dust particles – the researchers from Kiel’s materials science department would have been hard-pushed to find a more suitable place than Iceland. But no one was thinking of that when the team led by Rainer Adelung, Professor of Functional Nanomaterials, presented a new coating material at the 2018 Hannover Messe. The environmentally friendly, solvent-free marine paint was designed to prevent the high-maintenance settlement of mussels. This phenomenon is as well-known to sailors of small vessels as it is to those on ocean liners under the keyword "anti-fouling".

The research team is also working on other fields of application for the extremely smooth, resilient material system, ranging from medical vascular implants on which no biofilms can form to resistant coatings for wind turbines. The latter was just the thing for the Icelandic wind turbine manufacturer who visited the team at the international industrial trade fair for a chat. "The rotor blades of large wind turbines are constantly exposed to the weather. With rotational speeds of several hundred kilometres per hour, it's inevitable that they should wear out in the long run," Professor Adelung sums up the problem. If the surface becomes rough, moisture is able to penetrate. If this then freezes, the carefully and often manually balanced wings become unbalanced. "The rotor blades start to wobble, and may even eventually break off completely."

So the coating on wind turbine systems has to be renewed regularly. On off-shore installations in a sea climate, the blades are inspected every two years at the latest. Repairs are expensive. Not only is the system at a standstill for several days, but industrial climbing specialists need to be brought in to repaint the blades. "Then you have to allow around US$70,000 a day for the ship to take them out to the facility. And with the expansion of renewable energies, demand is going to continue to grow."

In fact, because of the extreme weather conditions in Iceland, much smaller facilities need checking after only about six months. Another factor is that they are often in isolated locations, for instance if they are being used to operate remote weather stations. "The more self-sufficient these systems are and the less often a maintenance team is needed, the better," says Professor Adelung. Following the Icelandic plant manufacturer's enquiry at the trade fair, the researchers developed their coating further in cooperation with Phi-Stone AG, a spin-off from Adelung's working group. Staff at the company tested sample coatings on a test plant in Iceland. The results after 24 months of testing were quite clear. "Unlike other coatings, ours were still intact. The customer was satisfied and is planning to go into series production," summarises Andreas Roth, board member of Phi-Stone AG. "And we now have the proof that the paint can cope with even extreme conditions."

Furthermore, the paint concept by the team from Kiel is five times more durable than commercially available offers. The reason for this lies at nano level: the researchers work with two plastic components that promise a particularly smooth, resistant surface in combination, but are usually almost impossible to mix. The secret: the team manufactures a special form of ceramic micro particle called a zinc oxide tetrapod and uses it as a binder. "Think of it as a tiny particle with four arms. If we grind them, we end up with interesting fracture edges that are highly reactive," explains Professor Adelung. As a result, they respond with other materials than the side surfaces of the arms.

Following this positive experience in Iceland, the next step is to coat wind turbines on the North Sea and Baltic coasts. Roth: "The 'noses' of high-speed trains are another possibility – in fact, anything that is exposed to strong forces and permanent abrasion."

Author: Julia Siekmann