The world’s biggest offshore wind farm opened in Thanet, seven miles off the Kent coast, yesterday.

The £780m scheme, built in two years by Sweden’s Vattenfall, consists of a hundred 115-metre turbines spread over 35 sq km and can generate enough power for 200,000 homes.

The Energy Secretary, Chris Huhne, said at the official opening of the site: “We are an island nation and I firmly believe we should be harnessing our wind, wave and tidal resources to the maximum.”

The 300 megawatts of electricity produced by the Thanet wind farm – plus the expansion of the Crystal Rig onshore wind farm in the Scottish Borders – takes Britain’s total installed wind power capacity to more than 5 gigawatts for the first time.

Wind power is now powering almost three million homes, according to the industry group RenewableUK. And delivery is accelerating as the industry expands: the turbines generating the fifth gigawatt have been installed within the last year.

Massive offshore installations such as that at Thanet are crucial if the UK is to meet green targets for 15 per cent of all energy to come from renewable sources by 2020. RenewableUK’s chief executive, Maria McCaffery, said: “Five gigawatts is an important milestone because it takes us within reach of our 2020 targets, while proving that each successive gigawatt takes less and less time to deploy.”