Molten salts, quartzite rocks, silica sand – these are all materials that have been tested or put to use to store heat produced at concentrating solar power plants. But researchers from the University of Arkansas think they have come up with a better way.
It’s concrete – a “special mixture,” mind you, that’s arrayed in a very particular way. Not only is it effective and safer, it’s also cheap, the researchers say.
The researchers say that a thermocline system (hot on top, cold down below) using parallel plates made of their proprietary concrete in a single storage tank can conduct heat with an efficiency of 93.9 percent, while avoiding the issues associated with other materials, in particular packed rock.
“The most efficient, conventional method of storing energy from solar collectors satisfies the U.S. Department of Energy’s goal for system efficiency,” Panneer Selvam, professor of civil engineering, said in a statement. “But there are problems associated with this method. Filler material used in the conventional method stresses and degrades the walls of storage tanks. This creates inefficiencies that aren’t calculated and, more importantly, could lead to catastrophic rupture of a tank.”
The researchers said their tests confirmed that the concrete layers conducted heat without damaging the materials used for storage. And, they said, the cost of energy storage using this method is a mere 78 centers per kilowatt-hour, “far below the Department of Energy’s goal of achieving thermal energy storage at a cost of $15 per kilowatt-hour.”
Concrete as a storage medium isn’t without precedent. According to the National Renewable Energy Laboratory, the German Aerospace Center had as of 2010 been testing the performance, durability and cost of using solid, thermal energy storage media (high-temperature concrete or castable ceramic materials). But note that the German’s were going solid, whereas the Arkansas system employs plates.
The plates, by the way, were developed by Micah Hale, an associate professor of civil engineering, and have survived temperatures of up to 600 degrees Celsius, or 1,112 degrees Fahrenheit, the university said.
“Our work demonstrates that concrete is comparable to the packed-bed thermocline system in terms of energy efficiency,” Selvam said. “But the real benefit of the concrete layers is that they do not cost a lot to produce compared to other media, and they have the unique ability to conduct and store heat without damaging tanks. This factor alone will increase production and decrease operating expenses for concentrated solar power plants.”
The work at Arkansas was done with the help of a $770,000 U.S. Department of Energy grant, the university said.