MIT’s ‘Sun in a Box’ Could Solve Our Energy Storage Woes

The push toward renewable energy is essential to fight climate change, but it’s also a vital part of planning for future power needs. As the world needs more energy, we can’t let all this free solar power just bounce off the planet. Even if we develop more efficient solar panels, how do we store that power? Battery technology has lagged for years, but a team from MIT and the Georgia Institute of Technology may have the answer. They call it a “sun in a box.”

The most efficient and widely used batteries we currently have use lithium-ion technology to store energy. Even the best batteries degrade over time, lose power to heat, and lack the kind of energy density we would need for powering the grid. The device detailed in the new study serves the same purpose as a battery, but it’s not one. The sun box is an insulated graphite silo containing a slug of white-hot molten silicon. Its actual name is much less sexy: Thermal Energy Grid Storage-Multi-Junction Photovoltaics (TEGS-MPV). We prefer “sun in a box.”

According to the researchers, this sun in a box could store excess electricity for long periods as heat. So, you would use solar panels to power the grid, but the panels stop generating power when the sun goes down. However, you just need to make sure there are enough panels to produce excess power during the day. That power gets funneled into the sun box to heat up the silicon core. When the grid needs power at night, a multijunction photovoltaic system inside the silo captures light from the glowing silicone to convert it back into electricity. The system would work the same with wind power — you’re just heating up the silicon with power from a different source.

This approach is similar to molten salt energy storage. In that system, concentrated light heats salt to about 1,000 degrees Fahrenheit. Then you need to get that heat out as energy, the salt is pumped through a heat exchanger to create steam that spins a turbine. However, the temperature cap isn’t high enough to supply many homes when the sun goes down. The silicon core of the sun in a box could reach 4,000 degrees Fahrenheit or more.

Based on initial small-scale testing, the team estimates a single TEGS-MPV storage tank could store enough power to supply 100,000 homes overnight in combination with solar panels or wind farms. That’s a lot of homes that can run on clean, renewable energy 24 hours a day. These are just early tests, so it will be some time before anyone is ready to deploy a vat of molten silicon to your neighborhood. We can certainly hope, though.

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