Altamont Pass, California

Table of Contents


Altamont Pass wind turbines. (Source: Natur Cymru)
Altamont Pass wind turbines. (Source: Natur Cymru)

Altamont Pass (37°44'13" North, 121°39'5" West), a mountainous pass in Northern California, is home to one of the oldest wind farms in the U.S. and the largest concentration of wind turbines in the world. Altamont Pass is located one hour east of San Francisco, California and serves as a temperature buffer for the city by separating it from the heat of the San Joaquin Valley. Altamont Pass wind farm construction began in 1981 in response to favorable federal and state legislation that resulted from the energy price increases of the 1970s.

The Altamont wind farm consists of about 4,800 small wind turbines with a capacity of 576 megawatts (MW) annual generation of about 1.1 terawatt-hours (TWh) of electricity. The Altamont wind resource area is one of three primary regions, the others being Tehachapi and San Gorgonio. Together these three areas account for nearly 95 percent of all commercial wind power generation in California, and approximately 11 percent of the world’s wind-generated electricity. In 2004, wind energy in California produced 4,258 million kilowatt-hours of electricity, about 1.5 percent of the state's total electricity. That's more than enough to light a city the size of San Francisco.

Avian impacts

Wind resource areas in California. (Source: California Energy Commission)
Wind resource areas in California. (Source: California Energy Commission)

Early research on the avian impacts of wind energy indicated that the wind turbines at Altamont Pass killed more birds of prey than any other wind farm in North America. The site is located on a major bird migratory route and there are large concentrations of raptors in this area including the largest population of breeding golden eagles (Aquila chrysaetos) in the world. The California Energy Commission estimated that a large number of birds of prey were killed by the wind turbines at Altamont Pass every year in its early years of operation. As a result of these bird fatalities, controversy developed between wind energy proponents and environmentalists.

In 1994, shortly after raptor deaths in the Altamont Pass became a general concern, the wind energy industry joined with other stakeholders (government officials, environmental groups, utilities) to form the National Wind Coordinating Committee (NWCC), a multi-stakeholder collaborative aimed at addressing the wind/avian issue and other issues affecting the industry's future. NWCC has sponsored numerous meetings and academic papers to better understand wind energy's wildlife impacts, including updates to the environmental community about the latest wind-related research; events related to the biological significance of wind's impacts; and a wind project permitting handbook.

The National Renewable Energy Laboratory (NREL) produced a report in 2003 that estimated that somewhat more than 1,000 birds were being killed annually by the wind turbines in the Pass. One-half of the birds killed are raptors. This is significantly more than that estimated by studies in the 1990s. However, the study also estimated that only 24 golden eagles (Aquila chrysaetos) are killed annually, about one-half of that estimated earlier. The golden eagle is a protected species. Most of the raptors killed are red-tailed hawks (Buteo jamaicensis).

Altamont Pass wind farm.

The study also concluded that the mortality rate per turbine is nearly ten times that of the previous estimates. Earlier studies suggested the mortality rate ranged from 0.02 to 0.05 birds killed per turbine per year. The NREL study puts the death rate at 0.19 birds/turbine/year.

A Government Accounting Office (GAO) report identified several unique features of the wind resource area at Altamont Pass that contribute to the high number of raptor deaths. First, California was the first area to develop wind power in significant numbers and thus has some of the oldest turbines still in operation in the United States. Older turbines produce less power per turbine, so it took many turbines to produce a certain level of energy; today, newer facilities producing the same amount of energy would have much fewer turbines. For example, Altamont Pass has thousands of wind turbines—many of which are older models—whereas, newer facilities generally have significantly fewer turbines. The sheer number of turbines in Altamont Pass is a major reason for the high number of bird fatalities in the area.

Secondly, the design of older generation turbines, like those found in Altamont Pass, are more fatal to raptors. Specifically, early turbines were mounted on towers 60 feet to 80 feet in height, while today’s turbines are mounted on towers 200 feet to 260 feet in height. The older turbines at Altamont Pass have blades that reach lower to the ground, and thus can be more hazardous to raptors as they swoop down to catch prey. The relative absence of raptor kills at newer facilities with generally taller turbines supports the notion that these turbines are less lethal to raptors. Third, the location of the wind turbine facilities at Altamont Pass may have contributed to the high number of raptor deaths. Studies show that there are a high number of raptors that pass through the area, as well as an abundance of raptor prey at the base of the turbines. In addition, the location of wind turbines on ridge tops and canyons may increase the likelihood that raptors will collide with turbines. One reason why other parts of the country may not be experiencing high levels of raptor mortality is partly because wind developers have used information from Altamont Pass to site new turbines in hopes of avoiding similar situations.

A September 2005 decision by the Alameda County Board of Supervisors passed a plan currently being implemented, to protect birds in the Altamont Pass, requiring that half the turbines be shut down each year in November and December, and the other half shut down in January and February. In addition, the 100-200 oldest and most dangerous turbines will be removed, and the entire project must be repowered, with newer, larger turbines replacing the smaller turbines.

One area of success has been in sharply reducing raptor electrocutions. Information in the late 1990s led to a number of actions including insulating wires, covering some exposed infrastructure on poles, and installing overhead powerlines specifically designed to protect raptors. When new projects are built today, virtually all powerlines within the project area are buried.

Further Reading

Lowitz, Melissa (Lead Author); Cutler J. Cleveland (Topic Editor). 2008. "Altamont Pass, California." In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth August 27, 2006; Last revised March 25, 2008; Retrieved May 19, 2008]. <,_California>
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