'Sun in a box' promises cheaper renewable energy storage

December 06, 2018 // By Rich Pell
Engineers at MIT (Cambridge, MA) have proposed a renewable storage system design that would store solar and wind energy in the form of white-hot liquid silicon in heavily insulated tanks.

The "sun in a box" concept, say the researchers, could deliver the stored energy back into an electric grid on demand and should be less costly than alternative approaches. The new design stores heat generated by excess electricity from solar or wind power in large tanks of molten silicon, and then converts the light from the glowing metal back into electricity when it's needed.

Such a system would be much more affordable than lithium-ion batteries, say the researchers, which have been proposed as one viable method to store renewable energy. In addition, they also estimate that the system would cost about half as much as pumped hydroelectric storage - the least expensive form of grid-scale energy storage to date.

"Even if we wanted to run the grid on renewables right now we couldn't, because you’d need fossil-fueled turbines to make up for the fact that the renewable supply cannot be dispatched on demand," says Asegun Henry, the Robert N. Noyce Career Development Associate Professor in the Department of Mechanical Engineering. "We're developing a new technology that, if successful, would solve this most important and critical problem in energy and climate change - namely, the storage problem."

The new storage system design stems from research that looked for ways to increase the efficiency of a form of renewable energy known as concentrated solar power , which - unlike conventional solar plants that use solar panels to convert light directly into electricity - uses vast arrays of huge mirrors that concentrate sunlight onto a central tower, where the light is converted into heat that is eventually turned into electricity.

"The reason that technology is interesting is," says Henry, "once you do this process of focusing the light to get heat, you can store heat much more cheaply than you can store electricity."

Concentrated solar power plants store solar heat in large tanks filled with molten salt, which is heated to temperatures of

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