Fourth Power’s Thermal Battery Technology Promises Affordable Long-Duration Energy Storage
Fourth Power, a Cambridge-based startup, is pioneering a thermal battery system that could significantly reduce the cost of storing renewable energy. Leveraging molten tin heated to 2,400°C within argon-filled, hermetically sealed chambers, the company aims to deliver energy storage solutions that rival and potentially undercut the economics of lithium-ion batteries and peaking natural gas power plants.
How the Technology Works
The system stores electrical energy by heating blocks of carbon inside insulated chambers filled with argon gas. When electricity is needed, molten tin, maintained at extremely high temperatures, circulates through graphite pipes—chosen for their ability to withstand intense heat cost-effectively. The heat emitted by the white-hot tin is converted back into electricity using specialized thermophotovoltaic cells that capture infrared light.
Development and Commercialization Timeline
Founded four years ago, Fourth Power has spent the past two years refining its technology and is now preparing to build its first full-scale battery. The company plans to deliver commercial units by 2028, targeting a storage cost of approximately $25 per kilowatt-hour—roughly one-tenth the current cost of lithium-ion batteries.
“Our projections for these first-of-a-kind batteries show they will be cost competitive,” said Arvin Ganesan, co-founder and CEO of Fourth Power. “The markets we’re targeting have very high costs today, so there is significant opportunity.”
Performance and Efficiency
The batteries are designed for daily charge and discharge cycles, providing continuous power for eight hours or longer—double the duration typical of grid-scale lithium-ion solutions. The insulation system, made from petroleum coke, a byproduct of oil refining, minimizes energy loss to about 1% per day, maintaining stable temperatures.
Currently, the company is conducting rigorous testing on smaller prototypes to verify power output and system durability.
Funding and Partnerships
To support its scaling efforts, Fourth Power recently raised $20 million in a Series A Plus funding round led by Munich Re Ventures, with participation from Breakthrough Energy Ventures and DCVC. This follows a $19 million Series A round completed in 2023. The funds will be used to construct a 1-megawatt-hour demonstration battery and advance toward commercial production.
Outlook
By simplifying the supply chain and minimizing moving parts, Fourth Power believes it can achieve its ambitious cost targets. If successful, this technology could accelerate the transition to renewable energy by providing affordable, long-duration storage that enables solar and wind power to supply reliable 24/7 electricity.
FinOracleAI — Market View
Fourth Power’s thermal battery technology represents a promising advancement in long-duration energy storage, potentially disrupting both lithium-ion battery markets and natural gas peaking plants. The key impact drivers include the projected low storage cost of $25/kWh and the system’s durability and efficiency. However, commercialization risks remain, such as scaling challenges and market adoption. Investors and industry watchers should monitor prototype performance data and pilot project deployments over the next 12-24 months.
Impact: positive
