Tower construction occurred piecemeal at ground level for the 62-ft-sq base, which rises 80 ft before tapering into a 44-ft-sq modular column. The structures, which went up simultaneously, are constructed with tubing from 36 in. to 2 in. in dia. Each tower is crowned by a 2,200-ton Riley Power solar receiver steam generator, which is assembled in segments on the ground.

"Building on the ground is much safer and enables us to use a repetitive assembly-line approach that expedites progress," says Andrew Gillespie, Bechtel project manager. "We built ten 90-ton structures in a common area using a transporter to position them into place to be lifted by tower cranes."

Steam generators consist of three sections—an evaporator, super-heater and reheater—each made up of 32 panels. Water circulates through the heat exchangers, in which it reaches 1,022ºF, turning into steam. High pressure, in turn, travels down the pipes to ground level, where it drives three Siemens SST-900 turbines to generate electricity. It will connect to a new 220/115-kV Ivanpah substation, built by Southern California Edison under a separate contract.

The process, also known as the "Rankine cycle," is similar to conventional powerplants, except it is fuel-free and thus considered to be more sustainable. Once the plant is operational, it will remove from the atmosphere the equivalent of emissions from 70,000 automobiles.

Turbines are air-cooled using condensers that turn the steam back into water. There are 13 storage tanks on-site with a combined 1.7-million-gallon capacity. They are designed for a variety of tasks, from washing mirrors to cooling turbines. While air-cooling cuts water use by 95%, it also reduces power and turbine efficiency. The Ivanpah Solar Electric Generating System will have a 28.7% gross annual solar-to-electricity efficiency rate.

“The air-cooled condensers and the use of vibration methods to place the heliostats are just a couple of the more environmentally-friendly methods we have employed at Ivanpah to help mitigate the project’s potential impact," says Paul Zavesoff, director of asset management with NRG Energy. "We have spent millions of dollars to ensure that the native species and plant life populations will not be negatively impacted by the project." In addition to maintaining the natural contours of the land and limiting the impact of construction, he says the project team has agreed to return the use to its previous state after the plant's usefulness has been exhausted.

The project's technology and low-impact design and construction "will encourage further innovations in the industry, which will help make the cost of solar competitive with other sources of energy," says Jeff Brightman, president of Bechtel's thermal business line.

The project has seen up to 2,000 craft workers during peak construction. The plant will generate an anticipated $650 million in total wages over its 30-year life cycle, including $250 million in construction, according to BrightSource.