Offshore wind farms move ahead full sail with underwater help

Europe is striving to cut the costs of operating wind turbines on water

Off the coast of Portugal, a team of underwater robots is scanning the base of turbines on a wind farm and looking for signs of damage while aerial drones check the blades. The activity is part of a project to reduce inspection costs, keep wind turbines running for longer and, ultimately, reduce the price of electricity.

Wind power accounted for more than a third of the electricity generated from renewable sources in the EU in 2020 and offshore wind energy is expected to make a growing contribution over the coming years. Denmark became home of the world's first offshore wind farm in 1991 and Europe is a global leader in the field.

Still, running wind farms in seas and oceans is expensive and adds to the overall cost of such clean power. Furthermore, Asian companies in the sector are gaining ground, increasing the European industry's need to retain a competitive edge.

Lower costs

‘Up to 30% of all operation costs are related to inspection and maintenance,’ said João Marques of the INESC TEC research association in Portugal.

Much of this comes from sending maintenance crews out in boats to examine and repair offshore-wind infrastructure.

The EU-funded ATLANTIS project is exploring how robots can help on this front. The ultimate goal is to cut the cost of wind energy.

Underwater machines, vehicles that travel on the water surface and aerial drones are just some of the robots being tested. They use a combination of technologies – such as visual and non-visual imaging – and sonar to inspect the infrastructure. Infrared imaging, for instance, can identify cracks in turbine blades.

Research carried out by the project suggests that robotics-based technologies could increase the amount of time that maintenance vessels can work on wind farms by around 35%.

Higher safety

Expense is not the only consideration.

‘We also have some safety concerns,’ said Marques, who is a senior researcher on the ATLANTIS project.

Having people transfer from boat to turbine platforms, dive beneath the waves to inspect anchor points and scale turbine towers is dangerous.

It is safe for people to transfer from boats to turbine platforms only when waves are less than 1.5 metres high. By contrast, robotic inspection and maintenance systems can be deployed from boats in seas with waves of up to 2 metres.

In addition, easier and safer maintenance will increase the amount of time that wind farms can be fully operational. In winter, it is often impossible to carry out offshore inspection and maintenance, which must wait for better weather in spring or summer.

‘If you have a problem on a wind farm or on a particular turbine in a month where you cannot access it, it needs to be stopped until someone can reach it,’ said Marques.

Being able to work in higher waves means that causes of wind-farm shutdowns can be tackled more quickly.

First of its kind

The project’s test site is based on a real offshore wind farm in the Atlantic Ocean, 20 kilometres from the northern Portuguese city of Viana do Castelo. It is the first of its kind in Europe.

‘We need somewhere to actually test these things – somewhere where people can actually develop their own robotics,’ Marques said.

In addition to its own robotic technologies, ATLANTIS aims to help other research teams and companies develop their own such systems.

European researchers and businesses active in this cutting-edge sector should be able to book time to use the facilities starting early this year.

Damage prevention

Another way to cut maintenance costs is by reducing damage and the need for repairs in the first place. The recently concluded EU-funded FarmConners project sought to do just that through the widespread use of a technology called wind farm control, or WFC.

When hit by wind, a turbine extracts energy from the airflow. As a result, the flow behind the turbine has reduced energy, a phenomenon known as shadowing. Because of this uneven distribution of energetic load on blades and towers, some turbines get damaged more than others.

WFC aims to balance out the distribution of wind energy throughout the farm, according to project co-coordinator Tuhfe Göçmen of the Technical University of Denmark.

There are several ways to mitigate the effects of shadowing. One is to misalign turbines. Instead of facing straight into the wind, a turbine can be turned slightly so that the shadow effect is steered away from turbines behind.

The pitch and the rotational speed of the turbine’s three blades can also be changed. While this cuts the amount of energy the turbine produces, it leaves more for the turbines behind to harvest.

Grid-friendly

As well as reducing wear and tear and maintenance costs, WFC can make wind farms more productive and help them generate power in a way that is easier for the electricity grid to handle.

Renewable energy including wind power is often produced in peaks and troughs. Sometimes the peaks, or surges in power, can overload the electricity grid.

With the turbines working together, power production can be levelled out to provide more consistent and stable input to the grid, according to Göçmen.

‘If we control turbines collectively, it is simply more efficient,’ he said.

Research has shown that such wind-farm control could increase the power output of all wind farms in the EU by 1%.

That's equivalent to twice the output of a 400 megawatt wind farm, which would cost around €1.2 billon to build, according to Gregor Giebel, a FarmConners co-coordinator also at the Technical University of Denmark.

This technology is also simple to implement as most wind turbines can be controlled and adjusted to act in the ways needed by WFC. The wind farms need simply to update their control software.

There is a lot of commercial interest in WFC technology, making it a promising way for Europe to expand its use of wind energy, according to Göçmen,

It is ‘low-cost and potentially high-gain,’ he said.

Author: MICHAEL ALLEN

This article was originally published in Horizon, the EU Research and Innovation Magazine.