The Rio Mesa Solar Electric Generating Facility has been proposed by Oakland-based BrightSource Energy in Palo Verde Mesa in Riverside County, about 13 miles southwest of Blythe.

The California Energy Commission staff has given its early assessment of a large solar thermal plant and has recommended a series of measures to pass environmental and other regulations.

In the preliminary staff assessment (PSA), Commission staff said, with exceptions in six technical areas, the proposed 500-MW solar thermal power project would comply with all applicable laws, ordinances, regulations, and standards (LORS) and that environmental impacts would be less than significant.

The six technical sections are: geology and paleontology, soil and surface water, traffic and transportation, transmission system engineering, water supply and visual resources.

If approved, the $2bn project would start construction in about a year. Construction would be staggered with the first solar plant scheduled to start the fourth quarter of 2013, while the second plant would begin the first quarter of 2014. The project would average 840 workers a month during construction, with a maximum of 2,188 at the peak. Up to 100 full-time employees would be needed when the project is operating, according to the applicant. Completion is expected in 2016.

The plant had originally been proposed a year ago as a 750-MW solar thermal plant that would have included one-third of it sited on federal lands managed by the Bureau of Land Management. BrightSource amended its application in July. The new project footprint removed the northernmost 250-MW section. The company made the change in response to issues raised during the early review process including cultural resources, biological resources, transmission corridor conflicts, and scheduling concerns from BLM.

The proposed project consists of two 250-MW solar plants. Each plant would have about 85,000 heliostats – elevated mirrors used to focus the sun’s rays on a solar receiver – that produces steam to generate electricity. The solar receiver is located atop a 750-foot tall power tower near the center of each solar field.

The proposed 3,805-acre site would be located on land leased from the Metropolitan Water District of Southern California. The company has agreed to sell power from Rio Mesa to Southern California Edison (SCE), a unit of California power company Edison International. (NYSE: EIX).

The PSA is being published in two parts. The second part, which will consist of staff’s alternatives analysis and the biological resources, cultural resources, and land use sections, is scheduled to be filed by October 15.

The Rio Mesa Solar Electric Generating Facility (Rio Mesa SEGF) is being proposed for development by Rio Mesa Solar I, LLC and Rio Mesa Solar II, LLC, subsidiaries of BrightSource Energy, Inc., a Delaware corporation.

The proposed project site consist of two 250-megawatt (MW) (nominal) solar concentration thermal power plants situated on the Palo Verde Mesa in Riverside County, California, 13 miles southwest of Blythe.. Both plants would be situated solely on private land leased from the Metropolitan Water District of Southern California. Only the project gen-tie line, emergency and construction electrical power supply line, and access road would be located on public land managed by the Bureau of Land Management. Each plant will utilize a solar power boiler, located on top of a concrete tower (approximately 750-feet tall), surrounded by heliostat (mirror) fields (approximately 85,000 per plant) which focus solar energy on the boiler. Auxiliary boilers will be used to operate in parallel with the solar field during partial load conditions and when additional power is needed.

Each 250 MW plant requires about 1,850 acres (or 2.9 square miles) of land to operate. A common facilities area will include a combined administration, control, and maintenance facilities, a water treatment facility, as well as a switchyard. The total area required for both plants, including the shared facilities and gen-tie line, is approximately 3,960 acres.

The PSA is available at:

After at least one public workshop and a public comment period on the PSA, Commission staff will release a final staff assessment (FSA).