With enough capacity to power two-thirds of the homes in Kent, the set of 175 turbines rising out of the Thames estuary officially became the largest offshore windfarm in the world on Thursday.

David Cameron was on hand to cut the ribbon on the London Array, a massive renewable energy project, in a move that industry sources hoped would herald renewed enthusiasm from the government for renewable power after the animosity to windfarms on the Tory backbenches.

"This is a great day for Britain and a big win for renewable energy," Cameron said at the opening ceremony. "London Array shows you can build large-scale renewable energy projects right here in Britain. This is because when it comes to clean energy, the UK has one of the clearest investment climates globally."

The project is owned by Denmark's Dong Energy, Germany's E.On and Masdar, of Abu Dhabi. Its 630MW capacity, enough to power 470,000 homes, has been fully operational since April, but on Thursday it was officially opened, by the prime minister alongside the climate change minister, Greg Barker. The consortium predicts that the windfarm will save 925,000 tonnes of CO2 a year.

"Such a strong signal from the very top of our political establishment will help to put an end to the siren calls from the naysayers who have failed to appreciate the scale of the opportunity Britain has here," said the RenewableUK chief executive, Maria McCaffery, in a statement. "We need to maintain our pole position in offshore wind energy to reap the full economic and environmental benefits."

The London Array has taken the crown of the world's largest offshore windfarm from the 500MW Greater Gabbard project off the East Anglian coast. The UK currently has more than 3.6GW of offshore wind power capacity, but is expected to have around 18GW by the end of the decade.

The news was welcomed by Greenpeace's executive director, John Sauven, who said the London Array demonstrated the UK's ability to deliver large-scale renewable energy projects.

However, he urged Cameron to accelerate the government's efforts to tackle climate change and cut emissions across the energy sector by agreeing to a target in the energy bill that would decarbonise the electricity sector by 2030.

"We're now world leaders in an industry that some wrongly dismissed in the past as a nice-to-have," he said in a statement. "But if offshore wind is to continue to provide jobs and economic growth for the UK and reach price parity with nuclear by the 2020s, David Cameron needs to do more than ribbon cut. He needs to give the sector long-term certainty by agreeing to cut carbon completely from our electricity sector."

Meanwhile, the last wind turbine was installed at the 325MW Thornton Bank offshore windfarm off the coast of Belgium, confirming that the project could now be expected to be commissioned in the coming weeks.

• First published by BusinessGreen