The Startup That Cracked the Code for Commercial Thermal Batteries

By Haley Zaremba - Mar 20, 2026

• Thermal batteries are emerging as a frontrunner in the energy storage market, capable of capturing excess renewable energy and providing heat for industry to reduce reliance on fossil fuels.
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• Fourth Power is innovating on thermal battery materials by using molten metal as the heat conductor, stored inside carbon bricks, and operating at extremely high temperatures (1,900-2,400°C) to achieve high power density.
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• The pursuit of high temperatures allows Fourth Power to shrink the system and significantly reduce costs on the balance of system, offering a major improvement over existing thermal battery concepts.
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Thermal batteries are the hottest new thing in energy storage tech. As energy storage heats up to be “clean energy’s next trillion-dollar business,” the private sector is throwing its full weight behind developing the technology that will unlock scalable long-term energy storage. As of 2022, the energy storage market was valued at nearly $198.8 billion, on track to reach $329.1 billion by 2032, and showing no sign of slowing from there. The race to corner that market is a contentious one, and thermal batteries are rapidly emerging as a frontrunner.

Thermal batteries hold onto excess energy in the form of heat, used for grid regulation as well as providing heat to power industry, which would otherwise be sourced by burning fossil fuels. The idea is that these thermal batteries would capture excess renewable energy when the sun is shining on solar panels and wind is roaring through turbines to create more clean energies than consumers can use concurrently, which the batteries could then dispatch as needed. 

In this way, thermal batteries could be an integral part of the clean energy transition when it comes to ensuring energy security in a rapidly changing power grid and improving energy efficiency in our residential and commercial buildings, as well as decarbonizing hard-to-abate sectors like steelmaking. In the industrial sector it could be pivotal to reducing dependence on fossil fuels as a heat source, which could have a major impact on emissions as industrial heat demand is expected to continue growing over the coming decade. 

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“Storing energy as heat isn’t a new idea—steelmakers have been capturing waste heat and using it to reduce fuel demand for nearly 200 years,” MIT Technology Review reported in 2024. “But a changing grid and advancing technology have ratcheted up interest in the field.”

And that interest is already starting to bear fruit. One of the biggest challenges – and opportunities – in the development of commercially viable thermal battery systems is finding the right materials. Storing superhot substances is obviously taxing to the materials involved, so finding the right ingredients to create an efficient, affordable, and long-lasting model is key.

Fourth Power, a thermal battery startup founded by MIT Professor Asegun Henry, thinks it may have cracked the code by turning standard engineering on its head. While many thermal batteries superheat gas or molten salt, which they store and transmit in metal pipes, Fourth Power is reversing the recipe by using molten metal as the heat conductor, which is then stored inside of carbon bricks. 

Henry has tested this approach before, in 2017, and it earned him a Guinness World Record for the hottest liquid pump. This also means that his model emitted a massive amount of light, which was used to break another record: achieving efficiency above 40 percent using a  thermophotovoltaic cell to turn light to electricity. 

“Explaining why our system is such a huge improvement over everything else centers around power density,” Henry was recently quoted in MIT News. “We realized if you push the temperature higher, you will transfer heat at a higher rate and shrink the system. Then everything gets cheaper. That’s why we pursue such high temperatures at Fourth Power. We operate our thermal battery between 1,900 and 2,400 degrees Celsius, which allows us to save a tremendous amount on the balance of system costs.”

While Fourth Power is a vanguard in the field of thermal batteries thanks to its innovation around materials, it could soon be facing a much more crowded and competitive playing field thanks to artificial intelligence. “Finding new materials, catalysts or processes that can produce stuff more efficiently is the sort of ‘’needle in a haystack’ problem that AI is ideally suited to,” the Financial Times reported in a 2025 article about how AI could – eventually – save more energy than it consumes.

By Haley Zaremba for Oilprice.com