IN Brief:
- Fourth Power plans to energise a 1MWh demonstration system later this year at its Bedford, Massachusetts headquarters.
- The system stores heat in carbon blocks, circulates liquid tin through graphite components, and converts white-hot light back to electricity using thermophotovoltaic cells.
- The company is targeting modular storage from around 10 hours to more than 100 hours, with a larger 25MW and 250MWh configuration envisaged for commercial deployment.
Fourth Power is moving toward an integrated demonstration of its thermal battery technology, with a 1MWh system scheduled to come online later this year at the company’s new headquarters in Bedford, Massachusetts. The MIT spinout is targeting utility-scale storage by taking surplus electricity, converting it into heat, and storing that energy in graphite blocks at temperatures ranging from about 1,900C to 2,400C before converting it back into power when required.
The architecture is unusual in both materials and operating temperature. Rather than moving hot gas or molten salt through metallic piping, Fourth Power uses liquid tin as the heat-transfer medium within a graphite-based system. During discharge, that stored heat produces intense light from the white-hot infrastructure, which thermophotovoltaic cells then convert back into electricity. The underlying TPV work has already cleared an important benchmark, with the technology demonstrating cell efficiency above 40%.
Fourth Power says the thermal battery is modular, allowing power and storage sections to be scaled separately. In the configuration described by the company, one storage module paired with one power module delivers a 10-hour battery, while additional storage modules extend duration without requiring a full rebuild of the system. A future full-scale installation is expected to provide 25MW of power and 250MWh of storage while occupying roughly half a football field, with expected heat losses of about 1% per day.
The company is targeting utilities, power producers, and other large electricity users looking for longer-duration storage than conventional short-duration batteries typically offer. Fourth Power has also said the same core system could eventually be adapted for industrial heat or operated more like a thermal power plant, although its immediate priority remains the battery application. More on the technology platform is available on Fourth Power’s technology page.
