Cities and buildings are the largest users of electricity in our modern world, and consumption of electricity continues to grow. One of the challenges of the 21st century is to meet that demand for energy services in a sustainable way – in a way that doesn’t harm people or the planet.There are many parts to this challenge’s answer. One is to make sure that electricity comes from environmentally benign sources. Wind energy is a technology that is widespread in some European countries and is coming of age in the United States; it offers an increasingly cost-competitive option for generating power in a clean, domestic, inexhaustible way.Buildings can obtain wind energy in two ways: The first is utility-scale wind energy in the form of electricity that flows from “wind farms” into the common grid; customers receive it just like electricity from conventional power plants. The second is from on-site generation by medium or small wind systems that can meet a range of power needs.Utility-Scale Wind Energy, Green Power, and “Green Tags” Wind energy accounts for less than 1 percent of U.S. electricity. Renewable energy sources like wind, solar, geothermal, and biomass together generate between 2 and 3 percent of U.S. electricity, while hydropower (electricity from dams) currently provides 6 percent. For a building to be sustainable, a much larger share needs to come from renewable sources than that currently offered by the typical utility mix, even when that mix includes a higher share of renewable energy than the national average. Businesses can make up the difference by buying some or all electricity from wind through the voluntary purchase of green power.The U.S. Green Building Council (USGBC) has identified such green power purchases as one of the energy criteria developed for the Leadership in Energy and Environmental Design™ (LEED) rating system for a green building. By purchasing qualifying green power, buildings earn credit toward designation as a green building. Of course, green power purchases can also be made even if LEED accreditation is not sought.Voluntary green power programs are sometimes offered by the local utility, or in “deregulated,” restructured markets by retail energy service providers. Another option is the purchase of “green tags,” or renewable energy certificates – separate from the electricity that is purchased for the building. In all cases, it is recommended that green power be certified: See the Green-e certification program website at (www.green-e.org) for information on how to locate certified providers and green power products. On-Site GenerationIn a windy location with a suitable amount of open area, on-site generation can be an attractive option. The wind turbine (or turbines) may need to be a small distance away from the building in order to benefit from the best possible winds. The standard turbine consists of three blades and a generator, mounted onto a tower or pole, with a generating capacity varying from a few hundred kilowatts to several watts. Innovative on-site wind turbine designs are sometimes featured in green building proposals, but such designs have not been widely tested. The integration of building and wind power technology remains an exciting frontier.Information about wind energy, green power, and small wind systems is available from the American Wind Energy Association (www.awea.org). Information about green power can be obtained from the U.S. Department of Energy’s Green Power Network (www.eere.energy.gov/greenpower).Christine Real de Azua is assistant director of communications at Washington, D.C.-based American Wind Energy Association.