Is this the UK's most useless wind turbine? It cost £130,000 in subsidies last year... to raise electricity worth just £100,000

Passed by millions of drivers a year, it is one of England’s best known wind turbines. It is also one of its most useless.

According to latest figures, the 280ft generator towering over the M4 near Reading worked at just 15 per cent of its capacity last year. And although it generated electricity worth an estimated £100,000, it had to be subsidised with £130,000 of public money.

Since it was switched on in 2005, it has been given £600,000 in public subsidies while working at an average of 17 per cent of its capacity.

The revelation came as the Government pledged to crack down on ‘cash cow’ turbines in locations that simply are not windy enough.

Energy Minister Charles Hendry warned developers it was wrong for inefficient wind turbines to get ‘significant’ public subsidies.

The Reading wind generator, which is on a ‘green’ business park and is owned by the power company Ecotricity, is one of England’s flagship turbines, visited by 20,000 schoolchildren a year.

At full power it can generate two-million watts (two megawatts) of electricity at any given time. Its annual output is calculated in megawatt-hours (MWh) – the total number of megawatts measured in hours.

The Renewable Energy Foundation, using data from the regulator Ofgem, said it worked at just 15.4 per cent of its maximum capacity last year, producing 2,692MWh of electricity.

Under the Government’s Renewables Obligation Certificate subsidy scheme, paid for through household bills, owners of wind turbines earn around £48 for every MWh they produce on top of the cash they raise selling electricity.

Last year, Ecotricity earned £130,000 from the scheme, which is designed to give energy companies incentives to build wind turbines.

It is far more expensive to generate electricity from wind than it is from nuclear or fossil fuels. Without the subsidy system, energy firms would invest in cheaper ways to produce electricity, such as coal.

But critics say it distorts the energy market and is over-generous to companies that build turbines in areas with too little wind.

Lee Moroney, of the Renewable Energy Foundation, said: ‘If the goal is to reduce greenhouse gases then you should put wind turbines in the most efficient sites, rather than have a scattergun approach.