Micro-wind turbines often increase CO2, says study


David Cameron led the trend for "micro-wind" this year when he installed a turbine on the side of his west London home. But he may have been wasting his time and money. The Building Research Establishment Trust, which advises the government and private sector, has found that in built-up towns and cities weak winds and turbulence mean turbines are likely to add to, not subtract from, a home's carbon footprint.

The BRE took data from sites across Manchester, Lerwick and Portsmouth and analysed the likely performance of three models of turbine. In Manchester two-thirds of the 96 different options studied for siting turbines produced a carbon dioxide impact that could never be paid back. Building, installing and maintaining the units would, on balance, exacerbate global warming. The same was true in a third of cases in the coastal city of Portsmouth.

"Small windmills may work in the outskirts of Wick, but the current generation do not work well enough in built-up areas," said Martin Wyatt, the chief executive of the BRE Trust. "People need more information to ensure they are not doing the wrong thing."

After the energy used in manufacture from aluminium, steel, copper and fibreglass, the carbon footprint of the turbine is exacerbated by transportation to the site and the need for regular maintenance to moving parts which bear the strain of rapidly changing loads during heavy winds, the report found.

The likely output of a micro-wind turbine on a pitched roof house in a large city such as Manchester would be less than 150kWh a year; 2% of the energy consumption of an average house.

But in a windy location such as Wick in northern Scotland, the output is likely to be around 3,000kWh a year - about 40% of energy use. The carbon payback in this coastal town would come in less than a year in most cases, and after no more than seven years in the most difficult conditions.

Carbon dioxide embodied in the manufacture of the turbines ranged widely. In the best case it was 180kg - equivalent to the amount emitted in a 45-mile car journey. In the worst it was 1,444 kg, close to the impact of one person taking a return flight to New York. Delivery, installation and maintenance over a 20-year lifespan could add from 18kg to 147kg of CO2.