Fourth Power’s SF Thermal Batteries can be cheaper than expensive natural gas power plants

The fourth power take on long energy storage sounds like something from a James Bond movie. The thermal battery comes with a sealed chamber filled with overheated liquid tin and argon. However, the company’s goal is much more comfortable. It’s about storing electricity cheap enough to choose solar and wind 24/7.

Here’s how technology works: To preserve the energy, electricity from the grid heats the carbon blocks in an insulated chamber filled with argon gas. If power is required, the system pumps burnt molten tin to 4,352°F (2,400°C) via graphite pipes. This is the only cost-effective material that can withstand these temperatures. Special solar panel-like devices called “thermophobic cells” bring heat back to electricity by capturing infrared rays from incandescent tin.

The four-year-old Cambridge, Massachusetts startup has been improving its technology for the past two years and is now preparing to build its first full-fledged battery, such as the melted tin. As everything goes into the plan, the fourth power plan is to deliver commercially-scale batteries to customers in 2028 at a cost that could cover both lithium-ion batteries and peaking natural gas plants.

“Our forecast is to be the first in the first market — they’ll be a competitive cost,” Arvin Ganesan, co-founder and CEO of Fourth Power, told TechCrunch. “Our comps in these markets are very expensive.”

In normal operation, the fourth power is intended for daily charging and discharging, providing continuous power for more than about 8 hours. This is twice as long as most grid-scale lithium-ion batteries. Insulation systems made from petroleum coke (waste from petroleum refining) significantly stabilize temperatures and lose only 1% of the energy stored per day.

The company is currently undergoing extensive testing on smaller versions of the system. “We are currently running cycles to ensure we get the expected amount of energy and make sure our systems are durable,” Ganesan said.

In addition to these tests, the company designs a 1 megawatt-hour demonstration battery. To build that project, the fourth power raised $20 million in the round. It is calling for the series positively, the company told TechCrunch exclusively. The round was led by Munich RE Ventures with breakthrough energy ventures and participation from DCVC. The startup previously raised a $19 million Series A in 2023.

Ultimately, the fourth power expects that once it reaches large-scale production, the cost of using thermal batteries to store electricity will drop to $25 per kilowatt-hour, at the cost of one-tenth of a lithium-ion battery.

“There aren’t many moving pieces. There are no many players in the supply chain, meaning you can sacrifice your target in a fairly simple way,” Ganesan said. “I feel that the $25 goal is pretty easy to achieve.”