The Hidden Hills Solar Electric Generating System (HHSEGS) was a 500MW project proposed to be built in Inyo County, California, US. It was planned to include two solar power generating units of 250MW each.
In 2011, BrightSource filed a license application with California regulators to build the 500MW HHSEGS project, but the license was withdrawn in May 2015.
The HHSEGS project site was located 45 miles (72.4km) west of Las Vegas and 18 miles (29km) south of Pahrump, next to the Nevada border.
Through its wholly-owned subsidiary Hidden Hills Solar Holdings, Bright Source Energy (BSE) planned to build, operate and maintain the power project. The HHSEGS project cost was estimated to be $2.7bn.
Construction was scheduled to start in the third quarter of 2013 and was expected to be complete by the end of 2015.
The project was designed to serve more than 178,000 California homes during the peak demand hours of electricity. It was expected to reduce more than 500,000t of CO₂ emissions per annum and more than 17 million tonnes of CO₂ emissions in its 30-year lifecycle.
Pacific Gas & Electric (PG&E) planned to purchase the power generated from the project, under a power purchase agreement (PPA) that was approved by the California Public Utilities Commission (CPUC) in 2010.
Construction of the Hidden Hills solar power plant
The solar generating units of the proposed project were to be constructed simultaneously, which was expected to take roughly 29 months to complete.
It was expected to create more than 2,300 construction jobs and about 100 operation and maintenance positions. Construction jobs were supposed to mostly go to workers in the local area.
Hidden Hills solar plant details
The HHSEGS project was supposed to spread across 3,280 acres of land in the Mojave Desert, between Death Valley and the Nevada border.
The land is privately owned by the Mary Wiley Trust. In contrast, the transmission line and natural gas pipeline for the project were expected to be installed on public land in Nevada, which is managed by the US Bureau of Land Management.
Plant make-up of Hidden Hills solar power generating facility
Rio Mesa solar electric generating facility (SEGF) will consist of two solar power generating units with a combined production capacity of 500MW.
The project was to consist of two solar plants, each with a production capacity of 250MW. The northern solar plant was to cover 1,483 acres of land and the southern solar plant was to cover 1,510 acres.
Each plant was planned to have a solar power boiler or solar receiver steam generator (SRSG). Both SRSGs were expected to be situated on a 750ft concrete tower surrounded by a solar field comprising approximately 85,000 heliostats. Each heliostat was to consist of two elevated mirrors mounted on a pylon.
The heliostats were to concentrate sunrays onto the water-filled SRSG, which was supposed to produce superheated steam to drive the electricity-generating turbines.
An auxiliary gas-fired boiler for each plant for parallel operation during emergencies was also planned.
Around 140 acre-feet of water was to be used by the project annually. It was planned to include two main wells and two back-up wells to supply the water. An air cooling system was to be used to convert steam back into water for reuse.
The common infrastructure of the two solar plants, such as administration, warehouse, maintenance complex and switchyard, was expected to be accommodated in 103 acres in the south-eastern corner of the site.
Technology used for the Hidden Hills solar project
The Hidden Hills SEGF project was to be equipped with BrightSource’s Luz Power Tower (LPT) solar thermal system. The LPT integrated technology was to offer a high-efficiency solution for solar power generation, using solar energy to create high-pressure, high-temperature steam for electricity generation.
It was to include a tall tower to house a solar boiler, optimised solar field design and optimisation software that would allow mirrors to track the sun in two dimensions and reflect sunlight to the boilers.
LPT uses around 33% less land compared with a typical photovoltaic (PV) farm or a parabolic trough solar thermal plant.
Coupled with LPT, the Hidden Hills Solar plants were to be installed with a molten salt system, which is an innovative heat storage solution.
This molten salt system allows heat to be stored and released to create steam after sunset. The system includes placing two tanks of molten salt at the base of each power tower. Depending on the heat storage needs, a percentage of the generated steam will be diverted to a heat exchanger to increase the salt’s temperature.
Grid network for Hidden Hills solar power facilities
The Hidden Hills Solar plants were planned to be connected to a new substation through a 9.7 miles (15.6km) single-circuit 230kV transmission line. From there, power would have been transferred to Pahrump community and the existing Eldorado substation through a 230kV backfeed and a 500kV transmission line.
BSE approached Valley Electric Association, a Nevada-based, public-owned utility, to construct, operate and maintain the transmission infrastructure of the Hidden Hills Solar project.