Solar power may be clean and renewable, but solar panels are inefficient and do not work at night. Could concentrated solar power be the salty solution? That is the question researchers at the University of Arizona’s College of Engineering hope to answer with a $5.5 million research project funded by DOE.

Concentrated solar power, or CSP, is generated by mirrors — called heliostats — that focus sunlight on a receiver containing a heat transfer fluid that absorbs the energy, which is then used to produce steam to spin electric turbines.

The research program will investigate the composition, properties and costs of new molten-salt-based CSP heat transfer fluids, which must absorb, transport and store solar energy, and generate electrical power efficiently and cost effectively.

Photovoltaic systems such as solar panels can convert up to 15 percent of the sun’s energy into electricity, say the researchers, but that conversion can jump to 45 percent in CSP systems operating at more than 1,200°F (650˚C).

Photovoltaic solar energy is produced by direct conversion of sunlight into electricity while CSP systems convert light into thermal energy, which is further converted into electrical energy. These different systems share a common problem: the sun does not shine at night. To overcome this nocturnal drop in power generation capability, an objective of the research is to develop molten-salt-based CSP heat transfer fluids with low melting points and low corrosivity that can be heated to about 2,400°F (1,316°F). Temperatures thus have much further to fall before the transfer fluid cools and solidifies. Insulating the fluid storage tanks and circulation system will enable the stored heat to generate steam, and electrical power, throughout the night. The salts used in current CSP plants are nitrates, which can operate at a maximum of about 1,000°F (538°C) before they become unstable, Li noted.

The project was funded as part of the Department of Energy’s SunShot Initiative, in an effort to make solar energy cost-competitive with other energy sources by 2020. The research team will be led by energy expert Peiwen “Perry” Li, an associate professor in the UA department of aerospace and mechanical engineering. Li’s co-researchers in this department are professor Cho Lik Chan and assistant professor Qing Hao. The project also will involve several researchers from various engineering disciplines within the UA College of Engineering’s School of Sustainable Engineered Systems.