The world's largest offshore windfarm, which cost over £750m to build, is poised to open off the coast of Kent, with 100 turbines producing enough electricity to supply heat and light for 200,000 homes.

The Thanet facility, which is going through final testing by Vattenfall, its Swedish power company operator, arrives as the National Grid revealed that at one stage last week 10% of the UK's electricity came from windfarms.

But industry experts claim that the wider green revolution needed to meet EU renewable and climate change targets imposed by the European Union is still in danger from proposed spending cuts.

Chris Huhne, the energy and climate change secretary, will open the facility, which is 12km off Foreness Point, on 23 September.

The Thanet farm, which will be able to produce 300MW of electricity, will be the biggest offshore facility of its kind until the even larger London Array, which has an eventual goal of 340 turbines, is completed. It will dwarf the nearby Kentish Flats facility off Whitstable, also run by Vattenfall and using similar Vestas turbines.

Excitement about the potential for wind was heightened last week when the grid put out a statement that over a 24-hour period up to 10% of electricity came from wind and 4% from hydro.

Maria McCaffery, chief executive of RenewableUK, said the figures underscored the contention that wind and renewables were no longer "alternative" but core parts of the power sector.

"We are expecting to see the contribution of electricity from wind gradually increase over the next decade, to around 30% of the UK's total consumption. This news confirms that not only are the windfarms we have built so far starting to deliver, but that UK windfarm yields are the best in Europe, and comparable with established technologies such as hydro," she said.

Richard Fearnall of wind energy developer West Coast Energy said it "put to bed the myth" that wind power is not a vital part of the mix in achieving energy security and meeting our renewable targets. "Let's hope that the landowners, potential neighbours of new schemes and, in particular, local planning authorities are the ones who are most encouraged by the news and that they will actively help the UK towards our legally- binding 2020 target of generating 15% of our energy from renewable resources, much of which will be wind-generated."

But the euphoria was dampened by Lord Turner, chairman of the government's committee on climate change, who has written to Huhne, warning that a "step change" is needed if Britain is to meet its target of generating 15% of energy – not just electricity – from renewable sources by 2020. The UK generates only 3% on an annual basis, although last week's figure from the Grid shows that – on a temporary basis at least – that figure can be much higher.

The government is considering whether to cut grants such as the £60m earmarked to help construct port infrastructure that would be needed to support further North Sea windfarms.

Turbine makers such as Siemens have indicated that a cut could influence their plans to build plants in the UK.