Competition looks at access to wind farms in stormy weather

Technology to help engineers reach offshore wind farms in stormy conditions is the subject of a design competition by the UK Carbon Trust and eight industrial sponsors.

The ultimate aim is to improve the economics of offshore wind and several potential solutions have now been shortlisted by the Offshore Wind Accelerator programme, which oversees the project.

Each turbine in an offshore wind farm requires an average of four visits a year for routine maintenance, as well as unexpected downtime to replace components.

‘That might not sound like very much, but if you consider a wind farm with 400 turbines out there, then you are busy all year round,’ said Jan Matthiesen, manager of the Accelerator programme.

During downtime, the turbines are in an idle state, where the blades are turned out of the wind and the brakes are applied. ‘It essentially just sits there and waits to be fixed, which is costing you money,’ Matthiesen said.

Maintenance vessels are then launched from shore, that is, provided waves don’t exceed around 1.5m in height. This rarely happens with current farms, which are typically less than 25km offshore, but the next generation could be as far as 300km out with thousands of turbines, presenting greater challenges.

The aim of the project is to come up with a technology that can allow maintenance missions in wave heights of around 3m, which Matthiesen estimates would increase availability of the wind farms for maintenance by four per cent, in turn increasing revenues by £3bn.

He added that there have been various designs put forward, but the chosen solution will most likely incorporate permanent bases or motherships from which daughterships will launch then dock with turbine bases.

‘One particular aspect we looked at was how vessels are behaving when they are not moving — you need to find the right compromise,’ Matthiesen said. ’So they need to be fast enough to move around the wind farm, but they also need to be stable if they are not moving at all.’

Indeed, one shortlisted daughtercraft uses suspension inspired by Paris Dakar-winning rally cars. The prototype boat has six ‘legs’, which are in contact with the surface of the water and move independently to keep the body of the craft still during flight and while docked.

Another shortlisted design uses a giant robotic arm to transfer engineers and equipment from a daughtership to the turbine base.

‘Flexibility is obviously key, so it might be that your mothership has a range of different daughtercrafts, so you can deploy some that are relatively cheap to run, but can only operate if the weather is quite good and then you may have others that are more expensive, with more high technology, but can bring you to the wind turbines in more severe weather,’ Matthiesen said

The shortlisted designs, which are at various stages, will now be developed further with financial help from the Accelerator, which will eventually select technologies for commercialisation.