Fourth Power’s approach to extended energy storage could easily be mistaken for a gadget from a spy movie. Their thermal battery technology utilizes superheated liquid tin and airtight argon-filled chambers. Yet, the company’s real mission is quite practical — to make storing electricity so affordable that solar and wind power become clear-cut solutions for round-the-clock energy needs.
Here’s the process: Electricity from the grid is used to raise the temperature of carbon blocks inside insulated, argon-filled chambers for storage. When electricity demand arises, the system channels molten tin — heated to a blistering 2,400°C (4,352°F) — through graphite pipes, which are the only materials that can economically survive such heat. Special devices known as thermophotovoltaic cells, similar to solar panels, then transform the intense infrared radiation from the glowing tin back into electrical power.
This Cambridge, Massachusetts-based startup, established four years ago, has spent the past two years perfecting its technology, and is gearing up to construct its first large-scale battery system—complete with molten tin. If everything proceeds as planned, Fourth Power expects to roll out commercial batteries by 2028 at prices that could beat traditional lithium-ion batteries and natural-gas peaker plants.
“We anticipate that our first units to hit the market will be competitive in terms of cost,” shared Arvin Ganesan, co-founder and CEO of Fourth Power, in an interview with TechCrunch. “The comparable costs in these markets are quite substantial.”
In typical use, Fourth Power expects its system to charge and discharge every day, supplying steady electricity for about eight hours or longer. That’s double the duration most utility-scale lithium-ion batteries can offer. The insulation, crafted from petroleum coke — a byproduct of oil refining — helps maintain stable temperatures, with only about 1% of stored energy lost each day.
The company is currently putting smaller prototypes of the system through rigorous testing. “We’re now conducting cycles to verify we’re delivering the intended power output and to confirm the system’s durability,” Ganesan explained.
As these evaluations continue, the team is also engineering a 1-megawatt-hour demonstration battery. To fund this initiative, Fourth Power has secured $20 million in a Series A Plus financing round, the company revealed exclusively to TechCrunch. Munich Re Ventures led the investment, with Breakthrough Energy Ventures and DCVC also participating. Previously, the startup raised $19 million during its Series A in 2023.
Ultimately, Fourth Power’s ambition is that, with mass production, storing electricity in its thermal batteries will drop to just $25 per kilowatt-hour — a fraction of current lithium-ion battery costs.
“There aren’t many moving parts. The supply chain is straightforward, which makes it easier to reach cost goals,” Ganesan said. “We’re confident that achieving the $25 target is well within reach.”
