Watch: To lower CSP cost researchers say just add salt!David Wagman | August 08, 2019
Engineers from the U.S. Department of Energy’s Argonne and Oak Ridge national laboratories are drawing on nuclear research on salts to advance concentrating solar-thermal power (CSP) technology.
CSP uses the sun’s rays to create thermal energy that is used to produce electricity, then store it for use when it is needed. CSP works when mirrors reflect and concentrate sunlight onto a receiver, which absorbs the light, converting it into heat stored in a hot fluid. Similar to power sources, such as nuclear and fossil fuels, that heat turns turbines, generating electricity.
Scientists are turning to chloride salts, which can be heated to 750° C, as part of the process. At higher temperatures, CSP may yield efficiencies high enough to hit target cost ranges on the order of 5 to 10 cents per kilowatt-hour, as opposed to 10.3 to 18.4 cents per kilowatt-hour today.
(Read "A moonlit tribute to an Apollo pioneer.")
The most efficient CSP systems take advantage of a large temperature difference between the hot leg (the pipe section containing the highest-temperature fluids) and the cold leg (the pipe section that carries salt from the turbines after its heat has been transferred). James Willit, principal chemist in Argonne’s Chemical and Fuel Cycle Technologies division said "that big difference in temperature lets you generate a lot more electricity.”
In 2018, Argonne researchers joined a team from Oak Ridge, Virginia Tech and the University of Utah who are building a CSP prototype for high-temperature molten salt to test the concept’s performance. Argonne’s role is two-fold:
- Develop sensors that can track the composition of salt as it flows through the hot and cold legs of a looped pipe
- Remove salt impurities, such as hydroxychlorides and oxides that promote corrosion
The sensors measure electrochemical responses in the salt, gauging its health and spotting possible problems. When salt is exposed to water, for example, hydrochloric acid forms, which can corrode the CSP system’s metal pipes. This corrosion leads to the presence of chromium, iron and other structural metal ions in the salt, which can shorten the system’s life span. Once the sensors detect impurities, the system turns on a separate electrolysis system, which adds magnesium to the salt to remove the corrosive elements.
The work is also part of a larger, five-year program called Gen3 CSP to find the best approach to next-generation high-temperature CSP systems. The next steps for scientists at Argonne and Oak Ridge are to install the prototype’s major components, operate it successfully and complete initial testing.