Government plans to make it easier to install wind turbines on homes have been dealt a blow by a report showing that many of them may not even generate enough green electricity to counter the carbon emissions created by their manufacture and use.

The study by the Carbon Trust and Met Office found that, in urban and suburban areas, wind speeds are frequently not high enough to justify the energy expenditure needed to install the rooftop windmills.

It recommends that a height limit on free-standing wind turbines is raised above 11m in order to maximise generating capacity. However, this appears to clash with a recent Scottish Government consultation which sought to encourage so-called microgeneration by removing the requirement to obtain planning permission for turbines of less than 10m.

Proponents of wind microrenewables have hailed them as the frontline in the household green revolution and even as a potential alternative to nuclear energy. Their proponents include Gordon Brown and David Cameron while, in Scotland, former Engergy Minister Brian Wilson has had one installed on his home on the outskirts of Glasgow.

However, an interim report by government-backed research technical advice group Encraft earlier this year discovered stark differences between manufacturers' claims about typical wind speeds and those found in cities and low-rise urban dwellings. In some cases, the energy generated by the devices was insufficient to power a lightbulb.

The latest research does not condemn household turbines altogether, but says that rural areas could deliver four times as much electricity and carbon savings from them as in cities and towns.

Because wind speeds are generally higher in rural areas, installations in some parts of the countryside could provide electricity which was competitive in terms of cost with grid power, the report claims.

The Carbon Trust recommended that future grant schemes should have criteria for measuring the likely carbon savings of small wind turbines, to ensure grants are awarded to installations which are going to save "reasonable" amounts of CO2.

The report said that in theory, small-scale wind energy could generate some 41.3 terawatt hours of electricity - 12% of UK electricity consumption - and save 17.8 million tonnes of carbon a year in the UK. But with current electricity prices and the cost of small wind turbines, a fraction of that is deliverable