There's a new fluid coming to traditional solar thermal systems.
Tyco Flow Control has come up with a way to replace therminol, the oil in the tubes in parabolic solar thermal, with molten salt. Solar thermal developers already use tanks of molten salt to store heat collected in the daytime to produce power in the evening or night.
By deploying salt as the heat transfer mechanism inside the pipes of parabolic solar thermal parks, the efficiency of solar thermal power plants could inch up incrementally, because molten salt retains heat longer than therminol. This approach may also help parabolic solar technology, the reigning but aging standard in solar thermal, better compete against heliostats and some of the other new solar thermal architectures.
Iberdrola is already experimenting with this and Tyco is receiving orders from other developers, says Frank Gilhooly, Director of Global Sales and Marketing for the Power Business Unit of Tyco Flow Control. Molten salt will first be deployed in this manner in Spain, but may wind up being used in solar thermal parks in Middle East and North America.
In a traditional parabolic solar thermal system, curved mirrors collect heat from the sun and concentrate it on a pipe filled with therminol, an oil. The therminol absorbs the heat and later transfers it to water. The water turns into steam, the steam turns a generator, and electricity is made.
"The challenge is that therminol flows rather easily. Molten salt does not because it sets up," said Gilhooly. "You need to keep it hot enough to keep it flowing."
To that end, Tyco's Vanessa division, which makes valves, has worked with a thermal division in Belgium to devise a pipe that is wrapped with a cable called a heat tracing unit that keeps it warm. Everything is then wrapped in insulation. Some other companies have tried to heat the pipe with a companion steam pipe. Leakage, however, is a problem, along with the fact that most solar thermal parks are located in areas prone to water shortages and droughts.