Award Spurs Research on Storing Thermal Energy in Concrete

Engineering researchers at the University of Arkansas will receive a $770,000 award from the U.S. Department of Energy to develop a novel method of storing thermal energy in concrete. The award and research project are part of the federal government's initiative to develop technology for low-cost energy storage of solar power.

"Solar holds great promise as an alternative source of energy," said Panneer Selvam, professor of civil engineering and director of the university's Computational Mechanics Lab. "The government recognizes this and knows that we must move in this direction. The problem is that scientists and engineers have not yet developed technology that will allow producers to harness solar power efficiently. So, one area of emphasis to reduce costs is something called thermal energy storage, which is nothing more than developing effective and cost-efficient methods of transferring heat from collectors and holding it before sending it to generators. That is what we are trying to do."

Selvam, whose research has focused on thermal energy transfer and computational models of spray cooling for small electronic devices, collaborates with Micah Hale, associate professor of civil engineering. Hale works with structural materials, specifically high-performance and self-consolidating concrete. For this project, he will develop and test ultra-high-performance concrete, which are different types or mixes of concrete that can withstand high temperatures.

In Europe, concrete is a popular medium for thermal energy storage, Selvam said, but the practice has not caught on in the United States. Energy has been stored at a maximum operating temperature of 325 degrees Celsius at an estimated cost of $25 per kilowatt hour. Because higher temperature storage lowers cost, the researchers will experiment with storing heat up to an operating temperature of 500 to 600 degrees Celsius.

The researchers will then systematically test performance of the concrete mix under extreme temperature and evaluate the effect of high temperature, rate of thermal loading and effect of temperature cycles. The concrete will be used to study the performance of thermal energy storage at various charging and discharging rates. The researchers will test the transfer of heat into concrete using three methods: a simple one-tube system, a design including many tubes and a novel method without steel tubing. To aid tests, the Selvam will develop a computer model to predict heat-transfer rates with and without steel tubing.

Storage of solar power in concrete starts with the collection of heat in solar panels. The heat is then transferred through steel pipes into concrete, which absorbs the heat and stores it until it can be transferred to a generator. In short, Selvam and Hale's team will investigate better ways to transfer heat from the pipes into concrete.

Storage of energy from traditional sources costs approximately 7 cents per kilowatt hour. Current technologies used to store solar power cost between 13 and 17 cents per kilowatt hour. The goal of the Department of Energy is to achieve thermal energy storage at 5 cents per kilowatt hour for up to 16 hours by 2020.

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