Fourth Power lands $19 million for prototype facility

The Cambridge-based startup is betting thermophotovoltaic storage can support a transitioning grid.

December 12, 2023
Close-up of molten metal being poured into a mold

Photo credit: Gunther / Keystone / FPG / Archive Photos / Getty Images

Thermal energy storage startup Fourth Power said today it has raised a $19 million series A led by DCVC and Breakthrough Energy Ventures. The funding will support the construction of a prototype facility outside Boston, the company said, which the company anticipates completing in 2026.

Fourth Power’s thermal battery is designed to heat liquid tin and transfer it to modular stacks of carbon blocks, which glow white-hot. Thermophotovoltaic cells then convert that light into electricity, the company said, dispatching energy within seconds.

The company claims its solution is 10 times cheaper than lithium ion batteries, lasts for more than 30 years, and can store energy for over a month, discharging it at periods that can meet both short and long-duration needs. 

Thermophotovoltaic energy storage, while far from a new concept, is a long way from commercialization, and major breakthroughs are still happening. In spring 2022, for example, a team at MIT that included Fourth Power founder Asegun Henry said they managed to boost thermophotovoltaic efficiency levels to 40%.

And Fourth Power isn’t the only startup working on this “sun in a box” technology. In October, California-based Antora Energy, which is also backed by Breakthrough Energy Ventures, announced plans for a large-scale manufacturing facility in San Jose, which is expected to start churning out batteries in 2024.

However, while Antora is targeting industrial applications, Fourth Power is focused on grid-scale storage, a section of the market that’s had a very good year. Per Wood Mackenzie, grid-scale storage saw record-setting installation numbers in the second quarter of 2023, growing by 172% over the first quarter to 5,109 megawatt hours. Moving forward, grid-scale storage is projected to account for more than 80% of total installations between now and 2027.

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