Enel has inaugurated asolarthermal plant in Italy that could inch up the efficiency and output for traditional solar thermal technologies.
The 5-megawatt Archimede plant uses molten salt, rather than an oil called therminol, to transfer heat collected by parabolic mirrors to the boilers for making steam. The plant also sports molten salt storage tanks and a combined cycle gas facility so it can produce power on cloudy days or during the evening.
While solar thermal developers have used tanks of molten salt to store excess heat, they have not used molten salt as the transfer fluid that runs in the pipes that sit above the mirrors where heat from the sun is collected. By deploying salt as the heat transfer mechanism inside the pipes of parabolic solar thermal parks as well as a storage medium, the efficiency of solar thermal power plants could inch up incrementally, because molten salt retains heat longer than therminol. Thus, more heat could be ultimately exploited from the mirrors. This approach may potentially 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.
The problem has been that molten salt begins to clump up, creating problems.
"The challenge is that therminol flows rather easily. Molten salt does not, because it sets up," Frank Gilhooly, Director of Global Sales and Marketing for the Power Business Unit of Tyco Flow Control, told us a few months ago. "You need to keep it hot enough to keep it flowing."
Tyco developed a series of valves and other components for deploying molten salt in this manner. Tyco has been working with Iberdrola on a molten salt project. Expect to see molten salt deployed in the massive Desertec project, which promises to deliver gigawatts of power from North African deserts to Western Europe.
The Archimede plant consist of 30,000 square meters of parabolic mirrors and 5,400 meters of piping. The molten salt is heated to 550 Celsius, which is comparable and even higher than some of the new wave solar thermal concepts. Higher temperatures translate to more power. The plant was named after Archimedes, who in the third century B.C. proposed setting ships on fire by transferring solar heat with bronze shields. The archaeological evidence is scant that the Athenians actually adopted this method, but modern-day tests show it could have worked.