Fourth Power’s sci-fi thermal batteries could be cheaper than pricey natural gas power plants

Fourth Power, a Cambridge, Massachusetts startup, is developing innovative long-duration thermal batteries that use superheated molten tin and argon-filled sealed chambers to store and release electricity. The system works by heating carbon blocks with electricity inside insulated argon chambers; when power is needed, molten tin heated to 2,400°C circulates through graphite pipes, and thermophotovoltaic cells convert the heat’s infrared light back into electricity. This technology aims to provide continuous electricity for eight or more hours—double the duration of typical lithium-ion grid batteries—while maintaining energy losses as low as 1% per day thanks to insulation made from petroleum coke. The company has spent two years refining the technology and is preparing to build its first full-scale 1-megawatt-hour demonstration battery, backed by $20 million in Series A Plus funding led by Munich Re Ventures, with participation from Breakthrough Energy Ventures and DCVC. Fourth Power projects that its thermal batteries could be commercially available by 2028 at