Alta Mesa Project - Phase IV

The Alta Mesa Project - Phase IV is a 40 megawatt wind energy facility to be constructed in the San Gorgonio Pass near Palm Springs, California.

The Project includes 61 Vestas V47-660 kW wind turbine generators, each with a 47 meter (154 feet) rotor diameter and a rated output of 660 kilowatts. The V47 turbines will be mounted atop tubular steel towers with hub heights of 37 and 60 meters. Projected net generation is estimated to be approximately 140,000 megawatt-hours annually, or enough to furnish the needs of approximately 16,000 average California homes each year. The Project's quality wind resource, which averages approximately 20 miles per hour, is supported by 15 years of operating history from 159 wind turbines presently operating at the site.

A new Project-owned substation interconnects with the Southern California Edison electrical distribution system, and then to the California Independent System Operator transmission grid. Of the 61 wind turbines comprising the Project, 52 are on land owned by Mark Technologies Corporation (MTC), which is a wholly-owned subsidiary of TenderLand Power Company. Five of the wind turbine sites are on adjacent federal land controlled by and leased from the Bureau of Land Management (BLM), and four of the sites are on adjacent land owned by and leased from the Metropolitan Water District of Southern California. (The Colorado River Aqueduct runs in a tunnel deep beneath the site.) Most of the Project's wind turbines will be located along ridgelines to the south of the existing wind turbines at the site.

Alta Mesa Site Location


Existing wind turbines from Phases I, II, and III at the Alta Mesa site produce with an average annual capacity factor of 35% to 40%. Due to the favorable locations on the site to be used for the Phase IV wind turbines as well as advances in wind turbine design, we anticipate an annual average capacity factor for Phase IV of approximately 40%. These figures already include an allowance for wind turbine availability (97% assumed), wake effects between rows of turbines, and electrical losses on-site and at the project substation.

Major permits and approvals required for the Project include county land use permits, a BLM right-of-way grant, and interconnection with the serving utility. The status of each is described below.

  • Riverside County (for turbines on MTC and MWD land)
    • Environmental Impact Report completed, 1998 (State Clearinghouse Number 1998031149)
    • WECS (Wind Energy Conversion System) Permit: WECS #71, Revision #8, granted March 2002
  • BLM (associated with 5 wind turbines on BLM land)
    • Right-of-Way Grant, anticipated September 2002
  • Southern California Edison Company
    • Interconnection Facilities Agreement, completed February 2001
    • Service Agreement For Wholesale Distribution Service, completed February 2001
  • FAA aeronautical study conducted; no hazard to air navigation

Aside from TenderLand and MTC participants, the following team of consultants, advisors, and contractors:

  • Project Design:
    • Meteorological / Wind Energy Consultants:
    • Electrical Infrastructure:
      • Don Keef and Associates, Redding, CA
    • Civil Work and Foundations:
      • Patrick and Henderson, Bakersfield, CA
  • Construction:
    • Substation: TBD
    • Civil Work, Foundations, Erection, Commissioning: Modern Alloys, Stanton, CA. Modern Alloys has constructed each of the 159 wind turbines currently operating at the site, as well as hundreds of other wind turbines throughout California.
  • Permitting:
  • Operations and Maintenance: Vestas - American Wind Technology.

Wind Turbine Technology

The Vestas V47-660 wind turbine to be installed at Phase IV is the most popular wind turbine currently sold, and is manufactured and supported by the world's largest wind turbine manufacturer. The Vestas V47-660 wind turbine generator is a descendant of the Vestas V27-225 kW model, a successful wind turbine, 42 of which are currently operating at Phase III on the same site.

The V47-660 is based on over 20 years of Vestas' wind turbine experience, and features:

  • 3 fiberglass-reinforced blades
  • full-span blade pitch for power regulation
  • computerized control system
  • produces power at wind speeds of between 9 and 55 miles per hour

Several thousand V47-660 units are operating worldwide.

Cutaway View of a Vestas V47-660
Wind Turbine Generator


San Gorgonio Pass

The location of a wind power facility is a key element in a project's design. Alta Mesa is located in San Gorgonio Pass. The prevailing westerly winds in the San Gorgonio Pass occur because of a combination of atmospheric and geographic factors. As the air over the desert heats up, it rises, creating a pocket of lower pressure near the surface. This pocket, acting like a vacuum, pulls in cooler ocean air from the west. As the cooler air is funneled through the narrow pass between the San Gorgonio and San Jacinto mountains, it is compressed and accelerated. The prime wind season begins in March and continues throughout the summer with regularity. The extreme desert heat generates strong afternoon winds which persist into evening. These high and predictable winds, together with the region's proximity to energy markets, make the San Gorgonio Pass an excellent area for wind energy development. The Alta Mesa site is the premier wind location in the San Gorgonio Pass, located at the first plateau at the mouth of the Pass.


  Thousands of wind turbines have been installed in the San Gorgonio Pass area since the mid 1980s. Many of the early projects used wind turbines with ratings of 25 to 250 kilowatts. Recently some of the earlier projects have been "re-powered" with modern wind turbines in the 600 to 1500 kilowatt class. Approximately 500 megawatts of wind power is currently installed in the San Gorgonio Pass area.

Wind Turbine Locations

Alta Mesa Phase IV is a new project; it does not involve removal of existing wind turbines, but instead represents additional development in the same vicinity as existing wind turbines from previous phases at Alta Mesa.

Forty-eight of the 61 wind turbines which make up Phase IV are located along ridgelines which run southward from the top of the Alta Mesa. These 48 wind turbines have hub heights of 37 meters. The balance, 13 wind turbines, are located near the top the mesa and have 60 meter hub heights. These 13 "tall tower" units are sited above existing wind turbines at the site in a "wind wall" configuration. The "wind wall" configuration, where new wind turbines are constructed above and between existing wind turbines, has been used successfully on Alta Mesa with Phase III development.

In addition to the wind turbines themselves, Phase IV includes:

  • A 45 MVA substation located on-site with 115 kV transformer, metering, buswork, reclosers, and 25 MVAR of switchable capacitor banks for power factor control.
  • Underground wire for power and communications.
  • 750 kVA pad-mount transformers, one located adjacent to each wind turbine.
  • A centralized computer monitoring and control system.

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