The wind blows everywhere on the planet. You might think, why not harness it for power in buildings? Typically, average annual wind speeds of 11 miles per hour are needed for commercial applications, while lower wind speeds can be used for water pumping and battery charging. Now, most cities are not built in places where the average wind speed (every hour of the year) is 11 mph; that's not really very comfortable. So the best wind resources are located away from cities, and the most cost-effective wind power comes from large-scale wind farms that feed the power generated into the electric power grid. On a good site with modern equipment, wind energy costs in the range of 5 to 8 cents per kilowatt hour, quite competitive with most new power sources.165
In fact wind power is the largest source of new renewable energy in the US, with nearly 2,500 megawatts (MW) of capacity coming online and feeding into the nation's utility grid in 2006 alone, representing an investment of $4 billion. According to the American Wind Energy Association, in 2006:
New wind farms boosted cumulative US installed wind energy capacity by 27% to 11,603 MW, the equivalent of 11 large coal-fired electric power plants. Wind energy facilities currently installed in the US produce about 31 billion kilowatt hours annually, enough electricity to serve 2.9 million homes.166
Some people advocate placing wind-turbine generators on top of buildings, but this is less cost-effective than in remote locations. First of all, these systems have to be small, which costs more per unit of capacity. Second, wind power increases with height, so taller buildings are better bets than smaller buildings. Third, in cities, upstream buildings can spoil the wind for downstream buildings, so the wind resource has to be evaluated with that in mind, for both existing and whatever future buildings might be erected in your area. Fourth, wind power increases at the cube of the wind speed: for example, a site that has 20% more wind speed (for example, 12 mph average vs. 10 mph) will deliver 73% more annual wind power! This basic characteristic of wind power means that only the windiest locations in the windiest cities are good candidates for this power. Fifth, wind power introduces new structural design considerations for buildings. As with photovoltaics, there are good reasons other than raw econom-
w ics to consider small wind systems for the tops of buildings, or for building sites, if they produce some energy and operate safely. First, they are very visible and therefore advertise the building's commitment to renewable energy. Second, they can be attractive visual elements, in this case a kinetic sculpture, that architects and building owners might want to use. Third, they provide a teaching tool about renewable energy for schools and environmental education centers. Nevertheless, internationally known wind expert Paul Gipe says, "Mounting wind turbines — of any kind — on a building is a very bad idea. I've yet to see an application where this has worked or will likely work."167
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