|Fig. 1: Altamont Pass wind farm as seen from a nearby cattle ranch. (Source: Wikimedia Commons)|
The Altamont Pass wind farm is located in the Altamont Pass of the Diablo Range in the San Francisco Bay Area, pictured in Fig. 1. With the first wind turbines being installed in the early 1980s, it is one of the earliest wind farms in the U.S. and represented more than half of the world's wind generation at the time.  Prompted by the 1970s energy crisis and the responsive policies that supported investment in renewable energy and required utilities to use renewable energy, the wind farm on Altamont Pass was one of the first in the world and remains one of the largest concentrations of wind turbines globally. 
The wind farm has more than 5000 wind turbines and the maximum amount of power the whole farm can produce is 580 MW.  The wind farm can thus produce a maximum yearly energy of
This maximum value does not account for losses that occur when the turbines are not spinning, when wind speeds are below average, or if turbines are performing under their potential. For instance, in 1985 and right after the wind farm was erected, only 1.36 × 1015 J were produced.  Despite this initial low energy delivery, energy production on the Altamont Pass has only increased as the technology improves and the wind farm expands. 
According to the California Energy Commission, Alameda County used 10,815 GWh of electricity in 2016, which converts to 3.8934 × 1016 J.  Thus, at maximum, Altamont can only produce roughly half of the amount of energy demanded by the county, requiring the rest of the energy to be sourced elsewhere.
There are currently several repowering projects in the Altamont wind farm. The old generation turbines, which have electrical generation capacities ranging from from 40 to 400 KW each, are being replaced with larger and more cost-effective units, with generation capacities ranging up to 3 MW.  Thus, this process of repowering the wind farm allows Altamont Pass to harness a much greater portion of the wind energy. The repowering differs through the wind farm as the turbines are owned by a variety of companies.
In general, repowering results in a variety of environmental benefits such as a reduced number of avian fatalities and a reduction in habitat fragmentation.  The new turbine technology also decreases fire hazard from the old generation electrical line failure and bird electrocution incidents.
|Fig. 2: Map of the Bay Area, with the Altamont Pass wind farm starred. (Source: A. Foster and Wikimedia Commons)|
California does not experience the highest wind speeds in U.S., wind energy capacity is actually concentrated in the middle of the country. Where California has an average wind speed of less than 5 meters per second, those speeds average above ten meters per second in the Great Plains. 
However, the Altamont Pass experiences high wind speeds due to the temperature difference between the Central Valley and the Bay Area. As California experiences an upwelling of cold, deep waters off its coast, the coast is uniquely cold while the Central Valley reaches high temperatures.  This temperature difference creates a gradient that funnels wind through the mountain pass from the coast. This phenomenon is particularly strong during the summer when temperatures inland reach their peaks. It can also be accelerated by the presence of an inversion layer in the Bay Area - in which cool, marine air becomes capped by warmer, denser air above, flowing inland from the hills and enabling more eastward flow.  The California Energy Commission (CEC) measured wind speed in the region before erecting the wind farm and found the mean wind speeds were at least 7.6 meters per second. 
Thus, the location of the wind farm, pictured in Fig. 2, enables it to support a wind farm. Furthermore, this location was ideal because the Pacific Gas and Electric Company (PG&E) had several high-voltage lines running through the Altamont Pass, making it a hub on California's electricity grid.  These large power lines connect the Altamont wind farm to all parts of California and meant that no new transmission lines needed to be built for the wind farm.
© Anissa Foster. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 D. R. Smith, "The Wind Farms of the Altamont Pass Area," Ann. Rev. Energy, 12, 145 (1987).
 K. S. Smallwood. "Wind Power Company Compliance With Mitigation Plans in the Altamont Pass Wind Resource Area," Environ. Energy L. Policy J. 2, 229 (2008).
 Statewide Energy Demand," California Energy Commission, November 2018.
 "Altamont Pass Wind Resource Area Repowering, Alameda County Community Development Agency, October 2014.
 E. Anderson et al., "Broad Overview of Energy Efficiency and Renewable Energy Opportunities for Department of Defense installations," U.S. National Renewable Energy Laboratory, NREL/TP-7A20-50172, August 2011.
 S. Wharton et al., "Measuring Turbine Inflow With Vertically-Profiling Lidar in Complex Terrain," J. Wind Eng. Ind. Aerodyn. 142, 217 (2015).