The next big things in renewables

In the world of the offshore wind turbine, size matters. Offshore turbines have always been larger than their land-based counterparts, but in recent years they’ve sprung up faster than a teenager in
a growth spurt. From the 3.6MW turbines that were state of the art around 10 years ago, the current installations at offshore windfarms under construction are 8MW units; to give a size comparison, the rotor on a 3.6MW turbine is about the size of the London Eye with the top of the uppermost blade 120m above sea level when it’s vertical, while an 8MW turbine is 222m from sea level to blade tip.

The reason is cost. It’s much windier out at sea than on land, even on the windiest day, and the larger the area swept out by the rotating blades, the more of that wind resource the turbine can capture. But cost comes into play because, although large turbines are of course more expensive then smaller ones, the costs for the entire installation don’t rise in a linear fashion. Large generators are cheaper per unit of torque than smaller ones, and the cost for the foundations, infrastructure and installation of a large turbine aren’t much higher than a smaller one. The feeling in the industry is that if you go to the expense of putting in the foundations for an offshore turbine and all the cabling, then it makes sense to put the biggest turbine you can on top of it to justify that outlay, said Tim Camp, head of turbine engineering at DNV GL, a Norwegian shipping organisation that has now branched out into renewable energy. The smaller the number of turbines a company needs to make up the generating capacity of a windfarm, the more cost-effective it’ll be and the lower the resulting cost of power: a very important consideration, as offshore wind is still the most expensive way we have of generating electricity. “We’re already talking to people about 10MW turbines and even bigger,” said Brent Cheshire, head of UK operations for DONG Energy, the Danish company that has built and operates most of the UK’s largest offshore windfarms, and is now installing Vestas’s MHI 8MW units at its windfarm extension projects at Walney, off Barrow-in-Furness, and Burbo Bank, in Liverpool Bay. “These really are very big beasts, but they genuinely do drive the cost down.”