Excessive subsidies make them an expensive and inefficient way of reducing greenhouse gas emissions, a study by the Renewable Energy Foundation (REF) think-tank says.

The report comes amid mounting disquiet over the number of wind farms planned for Britain.

Energy companies want to erect more than 3,000 turbines over the next five years, leading to fears that hundreds of acres of rural landscape will be blighted.

Critics insist that wind energy is too inefficient to replace the creaking network of fossil fuel power stations. Even with modern turbines, wind farms are unable to operate at full capacity because of the unreliable nature of Britain's wind.

The industry admits that for up to 30 per cent of the time, turbines are idle because wind speeds are either too low to turn the blades, or too high, risking damage to the machines.

Without any suitable method of storing the excess power produced when winds are blowing but electricity use is low, many turbines also have to be turned off for fear of overloading the grid.

The report says that wind farms are unprofitable and rely on hefty subsidies that ultimately come from consumers in the form of rising energy prices. This cost comes on top of increases in gas and electricity prices caused by the high price of oil. They risk leaving the poorest members of society struggling to heat their homes.

The report, written by John Constable, of REF, and Robert Barfoot, the chairman of the North Devon branch of the Campaign to Protect Rural England, says that the subsidy scheme is encouraging energy firms to build as many wind farms as possible because it is more profitable than investing in other more expensive forms of renewable technology, such as wave power.

They say: "The market for renewable energy is an artificial one created and maintained by government legislation. The question is whether this consumer-derived money is well spent. It is worth noting that the excessive subsidy offered to onshore wind development has drawn developers even to sites where the wind resource is very weak and the environmental impact severe."

Backed by large subsidies, companies have put in planning applications for 235 wind farms. The plans would see 3,189 turbines, many more than 400ft tall, installed by 2013. At present, there are 176 wind farms operating 2,033 turbines onshore and at sea, providing power for the equivalent of 1.42 million homes.

In 2006-07 more than £217 million was paid to energy firms under the subsidy scheme, known as the Renewables Obligation. Under the scheme, energy companies must obtain a proportion of their power from renewable sources, 6.7 per cent at present rising to 15 per cent by 2015. Those that fail to meet these targets pay a fine that is then shared between all the companies that have obtained energy from "green" sources. For every megawatt of green energy they sell, a company receives about £50 at present.

The Renewable Energy Foundation says that consumers ultimately end up funding the subsidies because energy firms that pay fines pass the costs on to customers.

The Campaign to Protect Rural England, which campaigns against the building of wind farms, attacked the rapid growth in the number being constructed.

A CPRE spokesman said: "There is a role for wind energy in providing electricity in the UK, but its intermittency and major visual impact limit the potential contribution of onshore turbines."

Other critics claim that wind farms pose a risk to wildlife such as birds and bats.

A spokesman for the British Wind Energy Association, which represents the wind power industry, defended the Renewable Obligation payments, claiming that they were necessary to help provide energy security. He said: "The question is whether we want to pay moderately higher prices to secure a secure and clean domestic energy source, or do we want to be dependent on imported fossil fuels?"

Critics have estimated that by 2020 the cost of the Renewables Obligation could rise to more than £3 billion.

The Department of Business, Enterprise and Regulatory Reform is reassessing the Renewables Obligation scheme. Proposed changes could mean that bands are introduced for different sources of renewable energy.