Liquid Sunlight that Powers Machine: Clean and Efficient

By Energy CIO Insights | Monday, February 25, 2019

In the current era where renewable energy is pushing past the use of fossil fuels, it is imminent to find a source to store the extra power being siphoned off of solar or wind power, to be used on nocturnal days. Making a better energy storage system is crucial, and this is where scientists at MIT came up with the concept of one such unit, "sun in a box"—he thought of a hot molten silicon sun powering about 100,000 homes sounds like a farfetched dream that will soon come to fruition.

The new system called thermal energy grid storage multi-junction photovoltaic, or TEGS-MPV in short, is based on molten salt batteries, which is inert and non-toxic. Use of molten salt battery represents the most efficient, flexible, and cost-effective form of large scale energy storage system to date. This type of storage enables stable and secure distribution of power without the need for any backup fossil fuel like natural gas.

There are many critical aspects of using molten salt batteries. The molten salt is circulated using heat exchanger pipes during the day and stored in tanks by night. Molten salt is stored at atmospheric pressure. Molten salt is stored at 556o C until a necessity for electricity arises, with or without the presence of the sun. Only 1o F of heat is lost per day. The salts used here can be used as fertilizers after the decommissioning of the plant.

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This particular source of renewable energy has many benefits. It can generate electricity when necessary, like nuclear and fossil fuel power plants, without all of the harmful leftovers and fuel costs. The plant can operate 24/7. Molten salt batteries are the lowest capital investment in an energy storage system. Storage allows the plant to produce over twice as much net annual output when compared to any other solar technology. The plant output makes sure to have a more secure and stable transmission system.

The alternative to salt was using silicon, which is abundant with almost 25.6 percent of the Earth’s crust comprising of it. Silicon can withstand temperatures over 4000o F. Fearing the storage of molten silicon in graphite tanks, as it could react to form something corrosive, but instead, silicon carbide formed lines a thin protective layer, rather than damaging the tank.

The sun in a box is like a giant rechargeable battery that stores excess electricity as heat. In the event of necessity, the photovoltaic inside the silo captures the glowing silicon’s light and converts it back into power.

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