Imagine a battery that works with molten metal so hot it looks straight out of a sci-fi movie. That’s exactly what Cambridge-based startup Fourth Power is building. Their “thermal battery” stores energy by heating blocks of carbon inside argon-filled chambers and later pumps liquid tin at 2,400°C (4,352°F) through graphite pipes. Special solar-like cells then turn that heat back into electricity.
The idea? Make renewable energy cheap enough to run around the clock, not just when the sun shines or the wind blows. Fourth Power says its system can last twice as long as today’s lithium-ion grid batteries and only loses 1% of its stored energy per day.
The company just raised $20 million in Series A Plus funding led by Munich Re Ventures, with Breakthrough Energy Ventures and DCVC joining in. They’re now working on a 1-megawatt-hour demo battery and aiming for commercial rollout by 2028.
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If successful, Fourth Power’s molten-tin tech could bring electricity storage costs down to $25 per kilowatt-hour, about one-tenth the cost of lithium-ion. That’s not just hot science… it’s a potential game-changer for clean energy.
