SolarReserve hopes to break ground on a 110-megawatt concentrating solar thermal power plant with salt-storage technology in July.
The project will sit on 1,776 acres of federal land next to the Crescent Dunes, about 175 miles northwest of Las Vegas. It will be the nation’s first commercial solar power plant using salt storage, which enables electrical generation after dark and during cloudy days.
The Santa Monica, Calif.-based developer was completing contract talks with an unnamed contractor at press time. Rocketdyne, a Canoga Park, Calif., rocket maker, developed the salty solution. The technology was successfully demonstrated during the late 1990s at an U.S. Department of Energy-backed 10 megawatt plant near Barstow, Calif. But it fizzled out.
"It operated for three years as a pilot project, but there was no real market for solar energy at the time. So, it was shutdown," SolarReserve CEO Kevin Smith said. "Around 2007, there was a renewed interest in solar power." Rocketdyne, now Pratt & Whitney Rocketdyne, a unit of Hartford, Conn.-based United Technologies Corp., struck a 20-year exclusive licensing deal with SolarReserve to develop the technology. The engineers that devised the salt-storage system also worked on the International Space Station and the Apollo lunar module.
The $750 million Crescent Dunes Solar Energy Project is seeking funding through an Energy Department loan program that nurtures new energy alternatives. SolarReserve has committed $250 million to the project. But the plant’s future hinges on federal aid. "We have been working with the Department of Energy for 18 months on our 1705 loan guarantee program application. If lawmakers cut the program for some reason, it would set the project back and potentially put it at risk," Smith said.
"Essentially, it’s just a guarantee on the debt that we would repay with interest." The project will create 600 construction jobs, plus 50 permanent positions when it’s finished in early 2013. The plant will also generate $37 million in sales and property tax revenues during its first 10 years of operation.
The plant will consist of a two-square-mile circular field of 17,000 heliostats, or 25-foot-wide tilting mirrors, that concentrate daylight to a receiver atop a 538-foot concrete tower that works like a lighthouse in reverse. Liquid salt circulates through the receiver’s heat exchangers where it reaches 1,050 degrees Fahrenheit to create steam, like that coming from boiling teakettle’s nozzle, and drive a turbine to generate electricity. Molten salt then returns to a pair insulated storage tanks at 525 degrees Fahrenheit for reuse hours and even days later.
SolarReserve already has a taker for the plant’s power. Tonopah Solar Energy LLC, a SolarReserve subsidiary, signed a 25-year power purchase agreement with NV Energy in late 2009. The facility will produce enough electricity for about 75,000 households annually, making it NV Energy’s second-largest renewable power source. Nevada power providers must get 25 percent of their electricity from green sources by 2025, as per a state mandate.
However, power from SolarReserve’s plant will cost about double the price of more conventional coal and gas powered options. Electricity from the Crescent Dunes plant will run about 13.6 cents per kilowatt hour, escalating at 1 percent for the next 20 years.
However, the plant operates free of emissions and fuel and therefore isn’t susceptible to peak-use pricing during the summer or oil-price volatility.
"The real question is what will natural gas cost in the future?" Smith said. "While fuel prices continue to escalate, we have a fixed price for 20 years and no emissions."
SolarReserve will build power plants designed as Solar Power Towers. This configuration captures and focuses the sun’s thermal energy with thousands of tracking mirrors (called heliostats) in a two square mile field. A tower resides in the center of the heliostat field. The heliostats focus concentrated sunlight on a receiver which sits on top of the tower. Within the receiver, the concentrated sunlight heats molten salt to over 1000 degrees Fahrenheit.
The heated molten salt then flows into a thermal storage tank where it is stored, maintaining 98% thermal efficiency, and eventually pumped to a steam generator. The steam drives a standard turbine to generate electricity. This process, also known as the "Rankine cycle" is similar to a standard coal-fired power plant, except it is fueled by clean and free solar energy. Other than the few unique components noted below, SolarReserve’s power plants are comprised of available materials, such as mirrors, and established technologies, such as steam generators and turbines. This will enable SolarReserve to provide electricity at or below prices from traditional sources such as coal or natural gas.
The unique components in SolarReserve’s power towers are the molten salt storage loop and the power tower central receiver. The molten salt storage loop enables the plant to generate electricity whenever it is needed – 24 hours per day or during "peak demand" periods. Molten salt is an efficient and inexpensive medium to store energy. The salt used in the process is an environmentally friendly mixture of sodium and potassium nitrate, the same ingredients used in garden fertilizer.
The other unique component is the power tower central receiver. This high heat flux hardware represents a unique blend of liquid rocket engine heat transfer technology and molten salt handling expertise. United Technologies has decades of experience with these technologies in both land-based and space applications, and its support will be invaluable to SolarReserve in developing power plants utilizing this revolutionary technology.