How can a solar power plant generate electricity at night?

Recent advances in solar power technology include use of liquid molten salt as both the energy collection and the storage mechanism in a solar thermal power plant. Concentrated solar energy heats a mass of molten salt to between 500 and 1000 degrees Fahrenheit. The heated salt is stored and can be used at any time to boil water for steam to generate electricity. This solves a major technological issue for solar power and allows the utility to continue to generate electricity from sunlight, even after dark. It also allows the solar plant to be used as a dispatch resource for the electrical grid. Thus, when the grid operator must quickly ramp-up power to handle a problem, the solar plant can be used rather than the traditional gas or coal plant.

Figure 1 ishows the the process diagram for a CSP plant using molten salt. Figure 2 shows the 110 MW Crescent Dunes Solar Energy Project located near Tonopah, Nevada, which is the largest CSP plant that incorporates such a storage system. It consists of a single 540-foot tall tower and approximately 174,000 heliostats. Enough salt is used to provide 10 hours of full load storage for grid stability and reliability. See Videos 1 and 2 for more information on the Crescent Dunes project and molten salt technology. The Crescent Dunes plant successfully synchronized with the grid in October 2015, and, then, as a fitting commentary on CSP with molten salt technology with 24 hour operation, generated its first electricity at 11 o'clock at night. Unfortunately, due to operating problems, including problems with the molton salt storage system, NV Energy terminated its power purchase agreement with Crescent Dunes after the project failed to generate the required amount of electricity, and the plant shut down in April 2019. And, given the dramatic drop in the cost of photovoltaic systems compared to CSP (see Fig. 3), it's future is uncertain, at least in the US. Elsewhere, the largest CSP plant in the world is being built in Dubai, and latest information shows that the cost of CSP has dropped dramatically in the last several years. Maybe CSP's future isn't as bleak as the Crescent Dunes experience might indicate.

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