Solar Sand

The same Middle Eastern deserts that have become synonymous with oil may soon be the key to expanding solar energy reserves as researchers turn to using sand as a storage medium for solar thermal energy. The results of a feasibility project known as Sandstock were recently released, which demonstrated the usability, practicality and stability of storing energy at temperatures of up to 1,000 degrees Celsius (1,800 degrees Fahrenheit).

The system was inspired by a traditional sand hourglass with two tanks – a cold tank on top and a hot tank directly below it. The cold tank is essentially a hollow cylinder that allows concentrated solar energy to penetrate. The heated sand moves by gravity to the hot tank where it can be discharged on demand. A three-step heat exchanger immersed in the hot sand produces super-heated steam that flows into a turbine to generate power. A mechanical conveyer then transfers the cooled sand back to the upper tank.

The types of sand best suited for the process are characterized using advanced microscopy to examine the size and shape of the grains and ensure that they can be transported via gravity efficiently. The method, which utilizes the sand both as a solar absorber and as a thermal energy storage material, could greatly reduce the cost of solar energy production. It has been estimated that, between the Middle East and North Africa, sufficient solar energy could be harvested to supply 50 to 70 percent of worldwide demand for electricity.