Of all the components in a wind turbine, the blades probably undergo the most stress through the machine's lifetime. And with more than 800,000 blades turning around the world, gaining access to monitor and service them remains an ongoing challenge.
Turbine manufacturers and service operators are now looking to use remote-controlled drones alongside existing methods, such as abseiling rope access or using telephoto cameras from the ground.
The use of drones in industrial applications is not new. Online retailer Amazon has considered them for delivering packages, while their military deployment has been well publicised in recent times.
Although relatively rare — a recent report from insurance underwriters GCube quoted an annual failure rate of 0.54% of the total in operation — blade breakages can be hugely damaging for wind-farm operators. Drones are being adapted to monitor and help avert this. They offer the ability to fly close to the blade while their high-resolution cameras arguably provide a greater degree of accuracy than the human eye.
Recent research from BTM Navigant estimated drone-inspection services for wind could become a $1 billion industry over the next five years. This will be split between the makers of the hardware, and the inspection-services companies that operate them.
A number of manufacturers, including GE, Vestas, MHI-Vestas and Siemens, confirmed to Windpower Monthly that they are investigating the use of drones for turbine inspections.
"We have positive expectations for drone technology and we are testing multiple solutions," said a Vestas spokesperson. "First and foremost, we would like to keep our service technicians on the ground and have a drone carry out the actual turbine scanning. With Vestas, safety comes first, and we expect drones to be able to help us continuously improve safety for our employees."
Siemens uses high-resolution cameras from the ground for blade inspections, which it considers "a fast and effective method". But the company says it is "looking closely" into the use of drones, indicating that it would not rule out their use in the future.
However, the sector is still in its infancy. The main challenges are the hardware of the machine and the software required for blade scanning.
One company that is addressing this is UK-based Flightkam, which is working on a prototype drone that scans each blade. It detects weaknesses by comparing it to the original blueprint of the blade.
"Take the human element out and it can be done - start to finish - with a report in around four hours," says Flightkam founder James Morphett. "Whereas it's around six hours to get access by sending an individual, and then they would have to write the report."
The system would be an improvement on current methods that still require a person to examine them. "But that's still great in terms of the speed it can be there, and there's no need to have anyone working at height, at the point of inspection," says Morphett.
Another challenge is the operating efficiency of the drones. "The platforms we use can operate in wind speeds of 12-15 metres per second," he says. "That said, the likelihood is you're going to do it when there's less wind because it will be safer and better for the operator from a cost perspective."
Drones could be particularly effective for offshore work, although the much harsher working environment adds further complications. However, Flightkam is working on a drone specifically designed for offshore use. It has sonic proximity detectors, as well as GPS, to maintain its position. This makes it heavier and more stable in high winds.
According to BTM, it is likely drones will supplement rather than replace existing access methods. The major growth area in the sector is likely to be in drone-services operators rather than drone manufacturers.
It is beginning to look as though a new sub-sector of the wind servicing industry has been created.