Engineers at Oregon State University (OSU) have discovered a new approach for storing concentrated solar thermal energy that could lead to reduced costs and widespread solar use.
The advance is based on a new innovation with thermochemical storage, which is a chemical that repeats cycles to hold heat, drive turbines and then gets re-heated to continue the cycle. This would commonly be conducted over the course of 24 hours, with variable levels of solar-powered electricity available at any time of the day, as dictated by demand.
According to the research, all of the energy produced could be stored indefinitely and used later when the electricity is most needed, or some energy could be used immediately and the rest stored for later use.
This kind of storage could make solar energy more widespread by eliminating the need to use the electricity immediately. 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.
Solar thermal electricity has been an interest among researchers because it has the potential to be much cheaper 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 can been used to heat a fluid that drives a turbine to produce electricity.
"With the compounds we're studying, there's significant potential to lower costs and increase efficiency," says Nick AuYeung, an assistant professor of chemical engineering in the OSU College of Engineering.
While cost, dependability and efficiency have been the primary constraints in solar technology, this new method is appealing because it is safe and long-lasting. It also eliminates greenhouse gas emissions.
"In these types of systems, energy efficiency is closely related to use of the highest temperatures possible," AuYeung says. "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.”
According to him, thermochemical storage resembles a battery, in which chemical bonds are used to store and release energy—but in this case, the transfer is based on heat, not electricity.
The system relies on the reversible decomposition of strontium carbonate into strontium oxide and carbon dioxide, which consumes thermal energy. During discharge, the recombination of strontium oxide and carbon dioxide releases the stored heat.
The new system could also allow a 10-fold increase in energy density since it is much smaller and would be cheaper to build. The system would operate at such high temperatures that it could first be used to directly heat air which would drive a turbine to produce electricity. Then, residual heat could be used to make steam to drive yet another turbine.
The researchers will need to take a look at making some adjustments when testing the system on larger scales and resolve issues such as thermal shocks, before a prototype would be ready.
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