A battery using liquid tin and Guinness World Record-holding technology to store energy at “almost half the sun’s temperature” has received funding from Bill Gates' energy innovation vehicle.

Boston-based Fourth Power announced today (Tuesday) that it has secured $19m in funding to scale its thermal battery technology.

The investment round was led by the venture capital firm DCVC, with participation from Breakthrough Energy Ventures – set up by Microsoft billionaire Gates to back promising energy technologies – and Black Venture Capital Consortium.

As well as scaling its technology, Fourth Power will use some funding to build a prototype facility outside Boston that it expects to complete in 2026.

Energy storage is vital for an energy ecosystem that is increasingly relying on intermittent renewable power sources such as wind and solar.

With the COP28 climate summit in Dubai looking set to adopt a text that calls for the tripling of renewable energy by 2030, means of storing excess wind and solar energy for calm nights when power cannot be generated are increasingly crucial.

Fourth Power’s system converts renewable energy to heat, or thermal energy, which can be stored until needed. The battery heats liquid tin and moves it through a piping system to heat stacks of carbon blocks until they glow white hot.

A visualisation of the white-hot carbon blocks that thermal energy would be stored in. Photo: Fourth Power

When power is needed, the system uses thermophotovoltaic cells to turn the light emitted by the glowing white hot plumbing system into electricity.

Fourth Power says this is like traditional solar generation but uses light from very hot graphite rather than light from the sun to produce electricity. The graphite reaches temperatures of up to 2400°C, with the sun's surface clocking in at 5,500°C.

Using “readily available and less expensive materials” enables electricity storage that is “ten times cheaper” than lithium-ion batteries, which dominate the market, claims Fourth Power.

“Fourth’s Power’s solution is an engineered sun-in-a-box,” said Zachary Bogue, co-founder and managing partner at DCVC.

“We are thrilled to join forces with this exceptional team, whose best-in-class technology can greatly increase the production and use of renewable energy.”

Fourth Power’s says its battery technology holds several records, including the Guinness World Record in 2017 for the highest temperature for pumping liquid metal at 1200°C.

On safety, Fourth Power says that because its system is not pressurised “there is no risk of explosion.” And as a “chemically inert system, there are no concerns of thermal runaway,” it claims.

“After more than ten years of research and development, we are grateful to reach this crucial milestone in our journey,” said Asegun Henry, founder and chief technology officer of Fourth Power.

Other energy storage technologies recently backed by Breakthrough Energy include a trailblazing “CO2 battery” storage system, iron flow batteries and iron air batteries.

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