Aerial photo of a wind farm along the Allegheny Front in southern Pennsylvania

The United States has the second most installed capacity of wind power in the world, after Germany. At the end of March 2008 the United States wind power capacity was 18,302 MW, which is enough to serve 4.9 million average households.^[14] Historically, the rise of wind farms in the US began in the late 1970s when the US government implemented favorable tax policies for wind investors as a reaction to the energy crisis of that era. Subsequent variability over time of the availability of government incentives, combined with an easing of energy costs led to an extended stagnation in the US wind energy industry in the following decades. In the mid-2000s, however, higher energy prices combined with an increase in demand for green energy (driven in large part by policy setting at the state level — such as the creation of statewide Renewable Portfolio Standards — in the absence of any materially significant or coordinated federal response to global warming) to result in unprecedented and accelerating growth in new wind development.

Currently, the largest wind farm in the US – and the largest in the world – is Florida Power & Light's Horse Hollow Wind Energy Center, located in Taylor County, Texas. The Horse Hollow project operates 421 wind turbines and has a capacity of 735 megawatts.^[29] Prior to Horse Hollow's completion, the largest US wind farm was the Stateline Wind Project on the Oregon-Washington line, with a peak capacity of 300 megawatts. Three California wind "farms" arguably have greater combined capacity than the Stateline farm, but are actually collections of dozens of individual wind farms. The California farms have many different owners and turbine types and have been constructed, retrofitted and occasionally dismantled since they were first installed in late 1982. As of 2005, all three of these areas are seeing renewed growth. Primarily, the older and smaller wind turbines are being replaced with much larger, more efficient models. Some of the workhorses of the past were only 65 kilowatts (kW) in capacity or even smaller, though some were several hundred kW. Today, the smallest utility-scale wind turbines are about 700 kW, with a few models approaching 5,000 kW (5 MW). Secondarily, non-functional turbines are also being returned to service.

Wind turbines in Solano County, California

Northern California is home to one of the earliest large wind farms. An advantage of the Altamont Pass Wind Farm is that under hot inland (Central Valley) conditions, a thermal low is developed that brings in cool coastal marine air, driving the turbines at a time of maximum electricity demand. However, this phenomenon is not always reliable and with an inland high pressure condition the entire region can be both hot and windless. At this time additional power must be provided by natural gas-powered gas turbine peaker plants. Solano County has one of the five major wind farms in California and has integrated the most advanced wind power technology anywhere in the United States. From 2003 to 2006, dozens of state-of-the-art turbines were installed at the Montezuma Hills near the Sacramento River delta. Eight of the turbines, at 415 feet tall, are the largest in the United States--and are 110 feet taller than the Statue of Liberty. These 3-megawatt Vestas wind turbines each produce enough power to meet the annual needs of more than 1,000 households.

Numerous small and fast turning wind turbines at Tehachapi Pass. (US) Today's turbines are larger and spaced farther apart, as that has proven to be a more cost-effective approach.

Even though California has some of the largest wind farms in the U.S., it does not have very many commercially viable wind farm sites, at least not onshore. Much of the Southwest is not much better, although there are some significant exceptions. The Great Plains states have an abundance of suitable sites for wind energy development^[30] however the region's potential is still largely untapped. Iowa and Minnesota are leading the Midwest in the development of wind energy with their combined capacities expected to reach 2,000 MW in 2007. The Pacific Northwest and the Northeast both have many excellent sites as well. In contrast, the Southeast has a very poor wind energy resource, though the Appalachian Mountains do provide a few good areas.

Currently, America's wind energy industry is an a period of rather rapid expansion. Although more and more wind companies are being founded, a relatively limited number of companies are headlining the industry's boom. Inside the industry, Florida Power and Light, Iberdrola, Invenergy, Enexco, and National Wind have emerged as apparent leaders.

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