An advance in the storage of concentrated solar thermal energy may reduce reduce its cost and make it more practical for wider use. Credit: Graphic by Kelvin Randhir, courtesy of the University of Florida
New approach for storage of concentrated solar thermal energy has been found, to reduce cost and make it more practical for wider use. The advance is based on thermochemical storage, in which chemical transformation is used in repeated cycles to hold heat, use it to drive turbines, and then be re-heated to continue the cycle. Most commonly this might be done over a 24 hour period, with variable levels of solar-powered electricity available at any time of day, as dictated by demand.
Conceptually, all of the energy produced could be stored indefinitely and used later when the electricity is most needed. Alternatively, some energy could be used immediately and the rest stored for later use. The underlying power source is based on production that varies enormously, not just night and day, but some days, or times of day, that solar intensity is more or less powerful. Many alternative energy systems are constrained by this lack of dependability and consistent energy flow.
In contrast to conventional solar photovoltaic cells that produce electricity directly from sunlight, solar thermal generation of energy is developed as a large power plant in which acres of mirrors precisely reflect sunlight onto a solar receiver. That energy has been used to heat a fluid that in turn drives a turbine to produce electricity. It’s safe, long-lasting, eco-friendly and produces no greenhouse gas emissions. Cost, dependability and efficiency have been the primary constraints.
“In these types of systems, energy efficiency is closely related to use of the highest temperatures possible,” Prof AuYeung said. “The molten salts now being used to store solar thermal energy can only work at about 600 degrees centigrade, and also require large containers and corrosive materials. The compound we’re studying can be used at up to 1,200 degrees, and might be twice as efficient as existing systems. The system is based on reversible decomposition of strontium carbonate into strontium oxide and CO2, which consumes thermal energy. During discharge, their recombination releases the stored heat. These materials are nonflammable, readily available and environmentally safe.
In comparison to existing approaches, the new system could also allow a 10X increase in energy density – it’s physically much smaller and would be cheaper to build. The proposed system would work at such high temps that it could first be used to directly heat air which would drive a turbine to produce electricity, and then residual heat could be used to make steam to drive yet another turbine.
In lab tests, one concern was the energy storage capacity of the process declined after 45 heating and cooling cycles, due to some changes in the underlying materials. Further research will be needed to identify ways to reprocess the materials or significantly extend the number of cycles that could be performed before any reprocessing was needed http://oregonstate.edu/ua/ncs/archives/2015/nov/storage-advance-may-boost-solar-thermal-energy-potential
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