Home wind turbines are generating a fraction of the energy promised by manufacturers, and in some cases use more electricity than they make, according to a study from consultant engineers Encraft.

The study said contrary to claims that micro turbines can suffice for a household's 30 percent electricity needs, on an average they only generate 214 watts hours per day, including when the turbine is switched off for maintenance or developed a snag. Sufficient power just to light up four low energy light bulbs for a day or less than a five per cent of electricity a household requires. Engineers however found that wind turbines installed on buildings in exposed positions or high up away generated significant amounts of energy.

The study, funded by the Pilkington Energy Efficiency Trust and the BRE Trust, looked at turbines made by five manufacturers in four rural, 10 suburban and 12 urban sites for a year.

Matthew Rhodes, Encraft's managing director said that turbines if put up in the right place can achieve the desired results.

"Sadly, an average semi-detached house, like the areas where most people live, where there are obstructions like trees and buildings, are poor locations," he told the Guardian. The "vast majority" of customers had been poorly advised. "There's a risk they will go off the whole agenda," he added.

For its part, BWEA reiterated the importance of site assessment in deploying small wind systems, following the launch of the Warwick Wind Trial report.

Commenting on the report, Alex Murley, BWEA Small Systems Manager said the results show that turbines need to be placed in environments that offer good wind speeds.

"The UK is the windiest country in Europe and there are thousands of such sites, many of which have been used to good effect and offer owners of small wind systems not just savings on their electricity bills, but an opportunity to export surplus energy to the grid."

According to BWEA, the majority of the turbines in the Warwick report were placed in an urban environment known to offer, on average, lower electricity yields than rural open spaces. Wind system installers and small wind systems suppliers recommend that on-site wind speed data and careful measurements are taken over a period of time prior to installation. Only four of the 26 sites where test turbines were placed have an annual average wind speed of over 5 m/s, considered a lower limit of commercial viability.

Murley added: "Over the last three years BWEA has developed robust industry standards for both products and installers, to better educate would-be consumers on what the technology can achieve, if sited and installed correctly. The overwhelming majority of small wind system installations are a success - when they are sited properly they save money and energy. The Warwick trials do not show that small wind is not viable. We know that it is, and the experience of thousands of UK users bears this out."