CITY College wanted to tick all the sustainability boxes when it built its new Innovation Centre in 2000.

It avoided expensive technologies like photovoltaic cells, which can take many years to pay back their installation costs. But, with the help of a Government grant, it installed two wind turbines.

The turbines have been valuable as a marketing tool – but not as a way of cutting energy demand.

The original grant application predicted that the two turbines would generate 33,800 kilowatt hours (KWH) a year, but the reality only delivers around 10,000KWH.

The neighbouring tower block turns Plymouth's prevailing southwesterly winds into northwesterlies and cuts the windspeed to the point where it's too low to justify having turbines.

"You wouldn't want to have turbines in an urban area unless they were so big that they were into the upper airstream," Mr Snook says.

Anyone thinking of installing a turbine should first fit a windspeed meter, an anemometer, to a stick as tall as the planned turbine and measure the wind in the proposed spot for at least a year, he says. Asked whether he agreed with the Bristol University engineering professor who recently called small scale wind turbines "middle class eco-bling", Mr Snook says: "That's not completely wrong."