Storing energy as heat via graphite and liquid metal

The system converts stored heat back to electricity through special solar cells

Spotted: In the US, demand for power from data centres and manufacturing is surging, threatening climate goals and straining power grids. Using fossil fuels to meet this demand would make these goals even harder to meet, but renewables are hampered by their intermittency and a lack of storage options.

Startup Fourth Power claims it has cracked this problem with a liquid metal-based energy storage solution. Fourth’s thermal battery stores energy in the form of heated graphite blocks. Molten tin, heated using electricity from solar panels or wind turbines, is piped around the blocks, which reach temperatures of around 2,400 degrees Celsius.

To discharge the battery, heat from the blocks is absorbed by the tin and piped through graphite stacks until they become white hot. Special photovoltaic panels tuned to infrared light then absorb the thermal energy emitted. The modular system, which is wrapped in insulation and kept free of oxygen, is able to store energy for over five hours before sending it back to the grid as electricity, with an efficiency of around 40 per cent.

The company, helmed by CEO Arvin Ganesan – who was previously the Global Head of Environmental and Energy Policy at Apple – raised $19 million in a series A funding round at the end of 2023. The round was led by DCVC, with participation from Bill Gates’ Breakthrough Energy Ventures and the Black Venture Capital Consortium.

Battery technology is increasingly looking for alternatives to lithium-ion. Some alternatives spotted by Springwise include thermal energy storage systems and storing energy in gravel.

Written By: Lisa Magloff