San Francisco may think it is on the cutting edge concerning urban wind farms (San Francisco tilts towards wind power, September 29, 2009), but the idea has long been tried and found wanting in Great Britain. The following critiques of urban wind power were all gleaned from the writings of wind power enthusiasts.
The first problem with urban wind turbines is the urban environment; buildings and other structures cause turbulence which reduces wind speed and causes it to swirl. The only rooftop wind turbines suited to a swirling wind are vertical axis (“eggbeater”) turbines, which are severely limited in size and are subject to frequent – and very expensive – gearbox failure.
Roof mounted wind turbines also are very noisy and produce heavy – and very annoying – vibrations. In an urban setting they may pay off on their investment in twenty years if they’re maintenance free, and none are. In urban settings small windmills usually don’t even pay back their carbon investment and are more likely to be net consumers of electricity than producers, since the inverter uses electricity when the turbine is not generating.
To operate efficiently, the larger the wind turbine the better, necessitating tall towers and long blades which are not appropriate in an urban setting. Manufacturers recommend that even small wind turbines be mounted on 80- to 120-foot towers to clear turbulence since nothing is generated until wind speed exceeds the cut-in rate of 7 to 10 mph. Such towers are unsuitable for installation on most rooftops.
San Francisco’s 44-member urban wind power task force producing a report recommending urban wind power is an illustration of how anthropogenic global warming inspires mass hysteria.