Researchers in Abu Dhabi are testing a pilot device that can store solar energy in sand to improve the efficiency of power plants and provide energy at night.

The technology, developed at the Masdar Institute of Science and Technology, uses gravity to drain sand from a higher basin into a lower one, heating up the sand grains with solar power during the transition. In the lower basin, the energy can be stored and withdrawn at low cost to provide extra energy if needed, for example during peak hours and at night-time.

“Two pilot models of the system have been tested in an effort to prove its efficiency and applicability on a large scale in big projects,” says Nicolas Calvet, an assistant professor at the Masdar institute’s department of mechanical engineering.

The next step is to test a more sophisticated model in preparation for its commercial marketing, Calvel says.

These tests will involve researching the thermal stability of sand and its specific heat-absorption capacity. The results showed a capability of storing thermal energy up to 800-1000 degrees Celsius.

Unlike traditional storage media used in thermal energy storage systems, such as synthetic oils and molten salts, sand is abundant in regions with plenty of sunshine, and inexpensive to obtain.

Explaining the method used to store energy in sand, Calvet toldSciDev.Net that: “The hourglass idea inspired the system, as it uses two reservoirs connected to one another vertically across a narrow passage that allows the movement of ‘cold’ grains of sand from the upper reservoir to the lower ‘hot’ one.”

The sand is heated by running cold sand through a solar heat collector, where it is heated before being stored in a hot reservoir. This hot sand can be used to run electricity-generating turbines.

The cycle is completed by returning the cooler sand to the upper cold sand reservoir, Calvet explains.

Amin Mubarak, a professor of mechanical power engineering at the engineering faculty at Cairo University in Egypt, says there have been several experiments around this technology in Europe and the United States.

However, “until now, they did not render any results that can be made available or capitalised,” he adds.

“There are challenges facing those experiments, the most important of which are the cost component of economic feasibility, and the method used to recover energy,” Mubarak told SciDev.Net. “Stored energy recovery process requires the presence of a fluid, either a liquid, air, or gas that is injected into the turbine. This process consumes a lot of energy, which raises the cost.”

Calvet admits that more research and funding is needed to commercialise the technology. “Securing funding poses a challenge as we need nearly US$300,000 to test the system in the pre-marketing stage,” he explains.