Seven kilometres off the west coast of Britain, 32 wind turbines spin gently in the breeze – each one so big they would tower over the London Eye. Located at Burbo Bank wind farm, seven kilometres from Liverpool Bay, they are the biggest turbines to be used commercially anywhere in the world. Each stands 195 metres tall – 53 metres taller than a standard turbine – with a diameter of 164 metres. The energy generated by one complete rotation can power one home for more than a day. “They’re extremely powerful machines,” says Benj Sykes, UK manager for offshore wind company Dong Energy, which operates the wind farm.
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For turbines, size equals efficiency. These ones are designed to turn more than 80 per cent of the time: when it is working at full capacity, the farm can meet the electricity demand of 230,000 homes. “It’s got a very big rotor, it’s more efficient at catching energy from the wind over a wider range of wind speeds,” Skyes explains. “They cut in at quite low wind speeds – four or five metres a second.”
Despite their huge size, the cost of construction – which includes putting down a foundation on the sea floor, running the cable that takes the electricity to an offshore substation, and building the steel tower and fibreglass rotor blades – is also lower than installing a standard sized turbine. “The more power you can get out of each turbine, the more power you can get out of each foundation, out of each array cable, and so it drives the cost down across all of those elements,” Skyes says.
The biggest challenge? Getting the turbines out to sea. “We use a very big vessel, called a jack-up vessel, which has legs at the corners so it can jack itself out of the water,” Skyes says. The vessels pick up the separate pieces of the turbines from Belfast before setting out to Burbo Bank. Once there, it jacks itself up and an onboard crane lifts the equipment into place. At the start of the project it took up to 36 hours to install one turbine. By the end they were installing a turbine a day.
In 2012, the clean energy industry set a goal of getting offshore wind electricity down to 100 GBP a megawatt in eight years. That milestone was passed in just five, and Skyes says giant turbines will help wind become one of the cheapest forms of electricity generation available. What’s more, they’re getting bigger: going up to 13 to 14 megawatts. “This has opened up a new stage in the lifecycle of the industry – we are confident that we’ll see turbine size continue to increase.”