Solar power has many fine attributes as a clean, renewable-energy source, but the major drawback for large-scale solar power is storing the electricity that is generated during the day so it can be used at night or when the utility needs it. The intermittence of solar photovoltaics (PV), the fact that production fluctuates during the day and is not available at night, is another major problem for electric utilities and power generators. Until now, the options have been either to use solar electricity as generated or charge batteries, which are currently too expensive for commercial utility-scale storage.

Finally, there is a practical solution to store huge amounts of solar electricity that is generated by large-scale solar plants—molten salt technology.

In mid-December, SolarReserve, a U.S. developer of solar power projects, received environmental approvals from the Arizona Power Plant and Transmission Line Siting Committee to build its Crossroads Solar Energy Project. The 150-megawatt project will be located in Maricopa County, Ariz., and uses an advanced molten salt technology developed by Pratt & Whitney Rocketdyne, a division of United Technologies, Hartford, Conn.

Crossroads is a central “Tower Power” type plant that captures and focuses the sun’s thermal energy by using thousands of tracking mirrors called heliostats that concentrate sunlight on a receiver atop a central tower. In the receiver, liquefied molten salt is heated to more than 1,000°F and then flows into a highly insulated, thermal storage tank where it maintains 98 percent thermal efficiency.

As needed, the molten salt is pumped to a steam generator, which drives a standard steam turbine to generate electricity. This process, known as the “Rankine Cycle,” is similar to a standard coal-fired power plant, except it is fueled by solar energy.

Crossroads will have the ability to store 10 hours of solar energy and generate electricity on demand, even after the sun goes down. This energy-storage capability provides stable, reliable electricity that can replace conventional power generation that produces harmful emissions from burning coal, natural gas and oil. When completed, the project will supply approximately 450,000 megawatt-hours annually of clean, renewable electricity, enough to power up to 100,000 homes.