April 13, 2017

The same visionary scientists responsible for pioneering space exploration are also behind a national effort to commercialize concentrating solar power (CSP) plants with integral energy storage. After years of research, testing and validating the technology, in late 2015 scientists working on the Crescent Dunes Solar Energy Project (Crescent Dunes) — a Nevada-based CSP plant — successfully reached commercial operation.

The journey to commercialization began nearly three decades ago, according to the U.S. Department of Energy.

In the 1990s, a group of scientists at Pratt & Whitney Rocketdyne worked with the DOE to develop breakthrough technology to collect the sun’s thermal energy and then store it in molten salt. From 1994 to 1999, Rocketdyne and DOE’s Solar Energy Technologies Office (SETO) built and studied a pilot project to validate technology — creating the world’s first molten salt receiver at Solar Two, a 10-megawatt (MW) test facility in the Mojave Desert.

One challenge remained: how to cost-effectively scale up and commercialize the emerging technology at the utility-scale.

With seed capital from investment firm U.S. Renewables Group and in partnership with Rocketdyne’s parent company United Technologies Corp., the company SolarReserve formed in 2008 to commercialize the technology. From early 2008 through 2011, SolarReserve worked closely with Rocketdyne to design a commercial-scale molten salt receiver assembly and an advanced heliostat control system that significantly reduced costs and had 10 times more capacity than the Solar Two pilot project.

In 2011, SolarReserve took the technology developed with SETO to the next level with financing from the Energy Department’s Loan Programs Office and began building Crescent Dunes. Located in Tonopah, Nevada, Crescent Dunes features a solar receiver that sits atop a tower and absorbs sunlight from over 10,000 mirrors. The mirrors follow the sun over the course of a day and magnify the sun’s power 1,200 times, heating molten salt to high temperatures.

This molten salt circulates through the tower and is then used to heat a steam cycle that generates electricity. The plant also features an automated system that controls the flow of molten salt to the receiver.

With the push of a button, plant operators manage dozens of valves and pumps to start, stop, and adjust the collection of solar energy and control electricity production. Despite changing weather patterns, the molten salt heats more than 60 million pounds of salt each day to reach a consistent 1,050 degrees Fahrenheit. The salt continually circulates in a loop, enabling its reuse by storing it in tanks for use at a later time.

In November 2015, Crescent Dunes successfully reached commercial operation every year delivers 110 MW of electricity, plus 1.1 gigawatt hours of storage under a 25-year power purchase agreement with NV Energy, the largest utility in Nevada.

Crescent Dunes was designed to meet NV Energy’s peak energy demand periods, extending into the evening hours until about midnight. To handle these demands when the sun isn’t shining, the plant’s energy storage integration delivers solar energy captured during the day to the grid during the late afternoon and evening when the demand for power is at its highest. The storage capacity of the plant is staggering. Every day, enough energy is stored at Crescent Dunes to match all of the utility-scale batteries in global operation — combined — at a fraction of the cost and with no degradation or replacement issues.

Since the molten salt absorbs 90 percent of the solar energy it receives and is used as both a heat transfer fluid and a storage medium, the plant is highly efficient. Crescent Dunes also eliminates reliance on fossil fuels as a backup energy source, enabling solar to operate as baseload generation and reliably deliver peak-period electricity to more than 75,000 homes in Nevada.