Renewable Electricity Systems - Micro Wind Turbines

Wind turbines create electricity from the kinetic energy of moving air. The power output of each turbine depends principally on three factors: the length of the blades, the wind speed (which varies from area to area as well as by height) and whether there's any air-flow obstruction from other buildings or trees. In short, the bigger and higher up the turbine, the better the result in terms of power generated per pound invested. Because of this, the ideal way to get involved with the installation of wind turbines is not to put one up yourself, but to join a community-owned scheme erecting commercial-scale turbines.

Unfortunately, community wind hasn't yet taken off in the same way that it has in Denmark and elsewhere. The next best option, if you happen to own a suitable piece of land, is to install a stand-alone turbine mounted on a mast. These range in capacity from around 600 watts to more than 20 kilowatts, with the masts ranging in height from around 3m to 15m. One of these could generate more than enough to match your total electricity consumption.

If, like most people, you don't have a suitable patch of windy ground to mount a turbine on a mast, then you could consider a truly micro roof-mounted model. The problem with these is that they don't tend to pro­duce very much power - especially on low buildings and in built-up areas where there's likely to be a lot of turbulence. The technology is gradually improving, however, and in a windy spot with a better-than-average tur­bine you might generate a decent chunk of your power requirements.

• How much power? As a guide, a small 1kW roof-mounted turbine with a 1.75m blade might realistically produce about 650kWh per year at an average wind speed of 4.5 metres per second. That's about 20% of a typical household's needs. Stand-alone turbines are far more powerful, though their outputs range widely according to position and height. An appropriately sited 6kW turbine with a blade diameter of 5.5m, raised 15m above the ground, should be capable of producing 7500kWh from an average wind speed of 5mps. This is about double the needs of a typical home.
• Space requirements: You don't need loads of space, but best results are achieved at 10m or more above surrounding buildings and trees - which is usually impossible with a roof-mounted turbine. In mounting any turbine, avoid sites with excessive turbulence, which will reduce performance and shorten the device's working life.
• Costs and grants: You should expect to pay about $3000 per kW, including the turbine, mast, inverters and batteries (if required). Large, stand-alone turbines may also require foundation work, which can cost an additional $3000. The Low Carbon Buildings Programme offers a grant of $1000 per kW installed, up to a maximum of $2500 and limited to 30% of the total project costs.
• Payback period: You might break even in fifteen to twenty years with a stand-alone turbine. Most smaller units struggle to pay for themselves during their lifetimes, though a steep rise in energy prices - or a generous feed-in tariff in 2010 - could change this.
• Maintenance: The service schedule will be specified by the manufacturer. At the very least an annual inspection should be performed to check for physical damage and wear.
• Planning permission: By the time you read this, it's likely that there'll be no requirement to seek planning permission for either roof-mounted or free-standing turbines, except in conservation areas. At the time of writing, however, it's still necessary to consult your local authority.
• Worth looking into? Probably not for rooftop installations, though perhaps for stand-alone turbines, depending on your budget and the average windspeed around your property.