Technology to harness solar energy after sunset

10 Aug 2011

Solar energy giant Brightsource, which is building one of the world’s largest solar thermal power plants (Ivanpah) in California’s Mojave Desert, is now developing a system called SolarPLUS, targeted at utilities, to generate power even when the sun is not shining.

Brightsource is liaising with utilities to clarify which future projects would best benefit from this technology, which combines its power tower solar thermal technology with two-tank molten-salt storage – the latter technology is a proven one that has been around for the past decade.

Molten salt storage, otherwise known as ‘solar salts’, is used widely in solar thermal plants in Spain. Solar salts are composed of 60pc sodium nitrate and 40pc potassium nitrate.

Combining its solar thermal technology with molton-salt storage, according to Brightsource, will extend the production of electricity into later parts of the day and after the sun sets when it is most valued by utilities.

It predicts that the SolarPLUS technology will reduce the cost of renewable power for utilities’ customers by increasing a plant’s capacity factor and by offering higher efficiencies than competing solar thermal power plants.

Brightsource also says its technology will offer utilities and grid operators extra operational and market value, by “providing balancing and shaping capabilities, as well as ancillary services to support a reliable grid”.

“Coupling storage with BrightSource’s high-efficiency LPT solar thermal technology represents a natural and critical advancement in utility-scale solar power generation,” said Israel Kroizer, EVP of engineering, R&D and product supply, BrightSource Energy and president of BrightSource Industries (Israel).

Brightsource is building the Ivanpah Solar Electric Generating System in the Mojave Desert. When construction of Ivanpah is completed, it is expected to nearly double the amount of commercial solar thermal electricity produced in the US today.
Brightsource LPT solar thermal technology

Brightsource Energy’s LPT solar thermal system harnesses the sun’s energy to create solar power. Image courtesy of Brightsource

Two new solar plants planned for California

The privately held Oakland, California-headquartered Brightsource has also filed an application with the California Energy Commission to develop two 250MW solar plants in California’s Inyo County.

If the project goes ahead, Hidden Hills will be poised on 3,280 acres of privately-owned land in Inyo County, California, adjacent to the California/Nevada border. The proposed site is situated south of Pahrump, Nevada, and west of Las Vegas, Nevada. In the past, the property has been used as an orchard.

The Hidden Hills Solar Electric Generating System (SEGS) will use the company’s next-generation plant design, which Brightsource says will take advantage of economies of scale – driving down the cost of energy while also reducing the project’s land use footprint.

For utility-scale solar projects of similar capacity, the new configuration reduces land use by 33pc or more compared to a typical photovoltaic (PV) farm and parabolic trough solar thermal plant, said Brightsource in a statement released on 8 August.

BrightSource is hoping to construct two separate 250-megawatt (nominal) solar thermal power plants, each with its own solar field and solar power tower. When complete, the two plants are expected to produce enough electricity to power 178,000 homes and avoid more than 500,000 tonnes of CO2 emissions annually.

Green collar jobs for California

According to the company, the Hidden Hills SEGS project has the potential to create more than 1,000 construction jobs at the peak of construction and about 120 operations and maintenance jobs.

Over the plant’s 25-year life, construction wages are expected to reach nearly US$160m, with total employee earnings estimated at nearly US$390, said Brightsource.

“The economic benefits that will be created by the Hidden Hills SEGS are significant, especially in the context of the economic challenges the region continues to face,” said Jeremy Aguero, principal analyst for Applied Analysis, a business advisory services firm that carried out an analysis of the economic and fiscal impacts of the Hidden Hills SEGS.

“After doing a detailed analysis of the HHSEGS, we expect the project to directly generate nearly 2,900 jobs related to onsite construction and the fabrication of materials over the two-year construction period, and contribute over $265m in local and state taxes over the plant’s lifetime. These new jobs and extra tax revenue will likely have a noticeable impact on the surrounding communities,” he said.

Solar field design

Brightsource says Hidden Hills will harness the company’s proprietary LPT solar thermal energy system, which generates power the same way as traditional power plants – by creating high temperature steam to turn a turbine – but using the sun’s energy rather than fossil fuels or nuclear power.

“At the heart of the LPT system is a state-of-the-art solar field design, optimisation software and a control system that allow for the creation of high temperature steam. The steam can then be integrated with conventional power plant components to produce predictable, reliable and cost-competitive clean energy,” the company added.

The new plant design at Hidden Hills will also feature a taller tower that allows for greater concentration of heliostats, which Brightsource says will significantly lower the amount of land required to produce energy.

The company is also planning to place mirrors on individual poles that are placed directly into the ground, allowing the solar field to be built around the natural contours of the land and avoiding areas of sensitive vegetation.

Closed-loop cycle

And in order to conserve desert water, Brightsource says Hidden Hills will use an air-cooling system to convert the steam back into water in a closed-loop cycle.

“By using air-cooling, the project will use only 140 acre feet of water per year, less than 10pc of the total amount of water used in competing solar thermal technologies with wet-cooling,” the company said.

Hidden Hills SEGS will provide power to Pacific Gas & Electric (PG&E) pursuant to two power purchase agreements approved by the California Public Utilities Commission in 2010.

Brightsource has 2.6 gigawatts (GW) of power contracts with Southern California Edison and Pacific Gas & Electric Company, California’s two largest utilities.

The company also manages an 110,000-acre development site portfolio in California and the US southwest, which it says has the potential to allow for about 11GW of installed capacity.

Photo: BrightSource Energy’s Solar Energy Development Center. Image (c) Eilon Paz and courtesy of

Carmel Doyle was a long-time reporter with Silicon Republic