Amazing renewable energy battery could power an entire city around the clock

7 Dec 2018

Image: © 安琦 王/

A new renewable energy battery concept using molten silicon could solve one of the biggest problems for grid-wide energy storage.

When Tesla first introduced its Powerwall concept, it advertised it as an answer to solving the problem of renewable energy storage in the home, whereby electricity generated using solar panels would not be wasted when not in use.

Now, a team from MIT is taking the same renewable energy storage concept and expanding it to a grand scale with a new, giant battery that could power a small city – not just when conditions are ideal, but all day and night.

On the face of it, the concept seems pretty simple, whereby excess electricity generated by solar farms or wind farms can be stored in large tanks of white-hot molten silicon. This then converts the light from the glowing metal back into electricity when it’s needed.

The researchers believe that such a system would be vastly more affordable than using lithium-ion batteries, this being another proposed method for large-scale renewable energy storage.

On top of that, they also estimate the molten silicon system would cost about half as much as the current cheapest form of grid-scale energy storage, hydroelectric storage. The team has called this concept Thermal Energy Grid Storage-Multi-Junction Photovoltaics, or TEGS-MPV.

“Even if we wanted to run the grid on renewables right now, we couldn’t, because you’d need fossil-fuelled turbines to make up for the fact that the renewable supply cannot be dispatched on demand,” said researcher Asegun Henry.

“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.”

Rendering of a cross-section of two large renewable energy storage tanks.

A cross-section of how the electricity storage system would look. Image: Duncan MacGruer

‘This is geographically unlimited’

The new system originated from a project that aimed to increase the efficiency of a form of renewable energy known as concentrated solar power. Rather than using photovoltaic solar panels, this system uses vast fields of huge mirrors to concentrate the sun’s energy on a single solar tower, using the heat to generate electricity.

Traditionally, solar plants stored this heat in large tanks filled with molten salt at temperatures of more than 500 degrees Celsius. When needed, the hot salt is pumped through a heat exchanger, which transfers the salt’s heat into steam to drive a turbine.

However, if heated beyond this temperature, the salt would corrode the stainless steel tanks, which pushed Henry and the team to find an alternative. This led to the use of silicon, which can withstand temperatures of more than 2,200 degrees Celsius. Once the team developed a pump that could withstand such extreme heat, the team then found a way to piece together graphite safely to produce a tank that would be room temperature on the outside.

Another benefit of the technology is that it can be paired with existing renewable energy systems, powering as many as 100,000 homes.

“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.”

Colm Gorey was a senior journalist with Silicon Republic