ROOFTOP wind turbines may have become the accessory of choice among “greener than thou” politicians, but a new study suggests that they are not only incapable of saving the planet but may even damage your house.

David Cameron, the Tory leader, and Malcolm Wicks, the energy minister, are two politicians who plan to mount the devices on their London homes in, respectively, Notting Hill and Croydon.

However, a study commissioned by Building for a Future, a journal specialising in sustainable construction techniques, has found that rooftop turbines are plagued by technical problems and seldom generate significant amounts of power, especially in towns and cities.

The report finds that a typical rooftop turbine produces no more than a quarter of the average home’s power needs, at best, and that in urban areas this is likely to be more like 10%-15%, because wind blows around towns in turbulent, unpredictable gusts.

In addition, older houses can face serious structural damage from the powerful sideways forces generated as the wind pushes against the turbines. This can be a particular problem if the turbines are mounted on chimneys.

In one paper Nick Martin, a construction expert on green building techniques, warns: “This is not the same thing as fitting a satellite dish. The lateral thrust exerted by these turbines on a Victorian chimney stack in a high wind would be more than sufficient to topple it. The same might be true of the gable ends of many older buildings.”

Martin also warns that the turbulence of winds in towns, due to roofs, chimneys and other obstacles, forces the machines to swing around constantly to “hunt” the wind, meaning the blades keep changing speed.

In his study, he writes: “Turbulence can wreak havoc on a wind machine, rapidly shortening its life and also drastically reducing the energy that is available.”

In another study Dr Derek Taylor, director of the Milton Keynes energy agency and principal partner of Altechnica, an environmentally friendly architectural practice, found that some owners had been forced to deactivate turbines because of the vibration.

Such risks are not yet widely known. Cameron, for example, is said to be planning to attach a wind turbine to the chimney stack of his £1m west London home, part of a £10,000 makeover that includes solar roof panels and rainwater recycling.

Similarly, Wicks has asked Croydon council for permission to put a small wind turbine on his garage in south London.

Wicks’s colleague Elliot Morley, the environment minister, is planning a wind turbine on his home in Scunthorpe, Lincolnshire, while Tim Yeo, Tory chairman of the Commons environmental audit select committee, hopes to install a windmill at his Suffolk home.

Told of the new study, Yeo said: “I have been keen to put one of these little wind turbines on my roof but there is a lot of emotion surrounding this issue and we need more numbers. It is no good doing it just because it feels virtuous.”

However, Colin Barden, a director of Eclectic Energy, whose StealthGen D400 wind generator is the design chosen by Cameron, said new models were overcoming many of the technical problems.

“Our turbine is designed for urban areas and can produce about a quarter of the needs of an average home. You cannot put them on some older buildings, but a good survey will ensure good siting and good results,” he said.

Both Martin and Taylor warn that perhaps the biggest issue of all is the price, with a turbine supplying a quarter of the power needs of the average British home costing between £2,800 and £5,000.

They argue that it would take 15 to 25 years to generate enough electricity to repay the outlay.

Barden said: “The costs are high but they will come down as more and more people buy them. This industry is still very young and has great potential.”

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