Rotor diameter is key for offshore wind turbines

Current wind turbine design is revolving around the 6 to 7 MW capacity range, with increasingly large rotor diameters.

But why go for a 7 MW wind turbine with a bigger rotor when a range of 3-5 MW designs are already available?

“There’s an offshore wind energy market kicking off,” Anders Bach Andersen of Vestas told Wind Directions magazine. “and in order to make that market reasonably competitive bigger wind turbines are needed. With bigger twind urbines you need fewer of them and you can reduce both capital and operating costs. But with fewer turbines you have potentially a smaller swept area at wind farm level so you need to compensate for that by equipping the machine with a larger diameter rotor.”

Vestas chose a rotor diameter of 164 metres based on a careful balancing act between the need for longer blades and pushing the supply chain for components, technical risk and the time it would take to bring a new design to market. The company will be making its own blades.

For its new 6 MW wind turbine, France-based supplier Alstom also began its design process with the rotor diameter, looking for a size that was affordable in terms of both risk and new technology.

“We had discussions with LM Windpower,” said Frederick Hendrick, Vice-President for Offshore, “and we both thought that 150 metres is a reasonable size for the next generation. So everything started from that.” The resulting 73.5 metre blades are the largest ever manufactured by LM.

Sarah Azau,