Widespread use of renewable energy is crucial to the carbon-free future we must achieve to curb climate change. Over the last four decades, it has become much cheaper but there are still small issues stopping it from becoming the exclusive source of power in our lives. A thorny one is its reliability. The tech is amazing but it depends on the Sun and the wind, so researchers are focusing on ways to store the energy produced and deliver it to consumers on demand.

A team of engineers from MIT have come up with a new conceptual design to do just that. As reported in Energy and Environmental Science, they plan to use the excess electricity generated to heat up white-hot molten silicon. Then when necessary the light emitted by the molten metal can be converted back into electricity.

This “Sun in a box” approach is expected to be cheaper than current solutions. The team estimates that it will cost about half as much as hydroelectric storage, currently the cheapest form of grid-scale energy storage. And it will be vastly cheaper than lithium-ion batteries.

“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,” senior author Professor Asegun Henry said in a statement. “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 project is called TEGS-MPV, which stands for Thermal Energy Grid Storage-Multi-Junction Photovoltaics. It would comprise two large tanks, one for the “cool” molten silicon (1,920°C; 3,500°F) and one for the “hot” molten silicon (2,370°C; 4,300°F). When electricity is needed, the hot silicon is pumped into tubes that can emit light, and the special multi-junction photovoltaics can efficiently convert it into electricity.

The team had to come up with innovative designs to test if this setup was possible. They constructed a small graphite-lined tank that can withstand the heat of the molten silicon, without any leaking on the outside. They also built a pump that is capable of dealing with such high temperatures, the highest tolerance ever achieved according to The Guinness Book of World Records.

Despite technological successes and challenges, the engineers are working hard on this project because it has the potential to change energy storage and could literally be built anywhere without the need for the damaging and costly dams that pumped hydro approaches require. The team thinks that a single TEGS-MPV could be used in a city with 100,000 homes that run exclusively on renewable energy.

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