The figure appeared to be a milestone. But it was followed by predictions that only 10% of all wind capacity will be available for use when the UK needs it most: in the depths of the coming winter. So which figure tells how close the UK is to achieving its targets on renewable energy?
The contrasting numbers explain why supporters of wind power – who say it will help combat climate change – and its opponents – who say it is an expensive and inefficient technology – always find something to lock horns about. While industry group RenewableUK will this week be celebrating the attainment of five gigawatts of wind capacity, detractors at the UK Independence Party (Ukip) are calling the claims a "tissue of lies".
The September record high for wind energy was reached because turbines were spinning at full pelt in windy weather while demand was lower than normal and other sources of power were not being used.
Critics argue that the unpredictability of wind turbines – which depend on the weather at any given time in a particular location – is nigh-on impossible for the grid to deal with. The grid says it assumes wind power is available at 30% of total capacity on average, but potentially at as little as 10%.
The latter figure compares with availability assumptions of 90% for coal or commercial gas and even 100% for electricity provided through the interconnector link with France. Grid figures for the past three months show wind providing 3,000 gigawatt hours of power, compared with 48,000 for gas, 49,000 for coal and 13,000 for nuclear. These numbers seem to show turbines providing the grid with less than 3% of its power. However, it is thought that half of all wind farms supply customers direct – circumventing the grid – so the overall number may be nearer 6%.