Wind power accounts for just over two per cent of America’s electricity, but this is growing. In 2010, 26 per cent of all new capacity came from wind. Many of the world’s largest onshore wind farms are in the US; the world’s largest, the Roscoe wind farm in Texas powers 250,000 homes.
Generation figures are similar in the UK and it’s estimated that wind power could provide 30 per cent of the UK’s electricity by 2020.
Onshore wind farms currently supply the bulk of wind-generated electricity. They’re much cheaper to develop than offshore farms (the sea is a hostile environment to work in).
Wind power is a function of the cube of the wind speed –double the wind speed and you get eight times the power. So not surprisingly the most important factor in building an onshore farm is the windiness of the site, followed by its consistency. Wind is an intermittent resource, but it still makes economic sense to go for sites that have a consistent breeze as possible.
With turbines, bigger is definitely better. The bigger they are, the more energy they produce. Rotor blades on the biggest turbines are now in the region of 80 metres long, producing up to 1.85MW of energy. Maximum output comes in at around 33 miles per hour, but you don’t want to site your windfarm in a location that’s too windy! If the wind speed goes above fifty miles per hour the turbines are shut down for safety.
Onshore wind farms have come in for public criticism in three main areas – the noise; possible harm to wildlife; and the intermittent nature of the wind.
The turbine blades cause the noise from wind farms as they pass around the tower. The ‘swooshing’ sound is undeniably noticeable, but not obtrusive. Some critics have said the sound is a health hazard, but there is no evidence to support this.
Wind farms have also been accused of being a hazard to birds and bats, with a danger of them flying into them. Again, evidence to support this is poor, and The National Academy of Sciences in America concluded that wind farms account for less than three in 100,000 of bird deaths caused by humans.
Wind intermittency (i.e. wind doesn’t blow all the time) is a criticism that also fails to stand up. When sited in a suitable location (strong, reliable wind) the turbines operate for around 75% of the time.