Skip to Content
77 Mass Ave

Sun in a box

MIT engineers draw up plans for a system to store renewable energy in white-hot molten silicon.
February 27, 2019
Annu Kilpeläinen

MIT engineers have come up with a conceptual design for a system that could store renewable energy and deliver it back into an electric grid on demand. Such a system could power a small city not just when the sun is up or the wind is high, but around the clock.

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. The researchers expect it would be vastly more affordable than lithium-ion storage systems.

The system consists of two large, heavily insulated, 10-meter-wide tanks made from graphite. One is filled with liquid silicon, kept at a “cold” temperature of almost 3,500 °F (1,927 °C). A bank of tubes, exposed to heating elements, then connects this cold tank to the second, “hot” tank. When electricity from the town’s solar cells comes into the system, this energy is converted to heat in the heating elements. Meanwhile, liquid silicon is pumped out of the cold tank, collects heat from the heating elements as it passes through the tubes, and enters the hot tank, where it is now stored at a much higher temperature of about 4,300 °F (2,371 °C).

When electricity is needed (say, after the sun has set), the hot liquid silicon—so hot that it’s glowing white—is pumped through an array of tubes that emit that light. Specialized solar cells, known as multi-junction photovoltaics, then turn that light into electricity, which can be supplied to the town’s grid. The now-cooled silicon can be pumped back into the cold tank until the next round of storage—so the system effectively acts as a large rechargeable battery.

“One of the affectionate names people have started calling our concept is ‘sun in a box,” says mechanical engineering professor Asegun Henry. “It’s basically an extremely intense light source that’s all contained in a box that traps the heat.”

Henry says the system could be sited anywhere, regardless of a location’s landscape. This is in contrast to pumped hydroelectric systems, currently the cheapest form of energy storage, which require locations that can accommodate large waterfalls and dams to store energy from falling water.

“This is geographically unlimited and is cheaper than pumped hydro, which is very exciting,” Henry says. “In theory, this is the linchpin to enabling renewable energy to power the entire grid.”

Keep Reading

Most Popular

A Roomba recorded a woman on the toilet. How did screenshots end up on Facebook?

Robot vacuum companies say your images are safe, but a sprawling global supply chain for data from our devices creates risk.

A startup says it’s begun releasing particles into the atmosphere, in an effort to tweak the climate

Make Sunsets is already attempting to earn revenue for geoengineering, a move likely to provoke widespread criticism.

10 Breakthrough Technologies 2023

Every year, we pick the 10 technologies that matter the most right now. We look for advances that will have a big impact on our lives and break down why they matter.

These exclusive satellite images show that Saudi Arabia’s sci-fi megacity is well underway

Weirdly, any recent work on The Line doesn’t show up on Google Maps. But we got the images anyway.

Stay connected

Illustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at customer-service@technologyreview.com with a list of newsletters you’d like to receive.