Bill Gates’ Breakthrough Energy Backs Startup That Uses Liquid Tin to Store Energy

Bill Gates’ Breakthrough Energy Ventures is backing a new thermal storage startup, expanding its investments in long-duration power backup.

Fourth Power converts renewable power to heat, storing it for future use. Relying on liquid tin, the thermal battery transfers heat to stacks of carbon blocks at extremely high temperatures, which can later be discharged as electricity through thermophotovoltaic cells. Doing so could help solve intermittency issues with renewables.

Investor DCVC led the Series A round of $19 million, with participation from Breakthrough and Black Venture Capital Consortium. Fourth Power plans to build a prototype facility that can store the equivalent of 1 megawatt-hour — enough energy to power about 1,000 homes — in Boston, with possible completion in 2026.

Breakthrough has backed several other startups in the thermal energy storage industry including Antora Energy, Malta and Rondo, in its bid to help emerging firms scale to advance low-cost utility-scale renewable grid. Fourth Power’s technology could be up to 10 times cheaper than other approaches to long-term energy storage, said Carmichael Roberts, who co-leads Breakthrough's investment committee.

“Thermal energy storage needs to exist for the promise of a true renewable grid, but it hasn’t been fully developed,” he said. “We see that as sort of open ground that we can go and make a big difference in.” 

Lithium-ion batteries are currently the most widespread energy storage. However, most lithium-ion batteries only have storage capacity of a few hours. There’s a growing need for long-lasting storage technologies as renewable energy puts more power on the grid. Doing so will help build up stores of renewable power for use when solar farms and wind turbines aren’t generating. Reserving energy as heat is one of the options that can help store a substantial amount for hours to days. 

“Thermal storage is an attractive technology because it can be flexibly sited, is relatively energy dense and can provide ancillary services,” BloombergNEF analyst Stephanie Diaz said. Startups using this technology raised $96 million in the three months ended September, their largest per quarter this year, according to data compiled by BNEF.

Breakthrough has also backed startups looking at other long-duration power storage technologies, including ESS and Form Energy. Both those companies rely on electrochemical processes.

“We try to look at early stage things where the founders are extremely talented but with some help, maybe they can develop something significant,” Roberts said. “We’re just equally as enthusiastic about things completely outside of thermal.”