ESS Tech is launching a 1.2-MWh sodium-ion battery system that can be stacked to deliver up to 4.8 MWh of energy in a standard 20-foot container, the company announced July 8. That capacity matches the latest version of Tesla's Megapack, one of the most widely deployed grid-scale energy storage systems on the market. The announcement adds to a growing list of sodium battery developments as utilities and large customers hunt for alternatives to the lithium-ion batteries that currently dominate energy storage.
The modular ESS Bridge product is designed for utility, commercial, industrial and data center customers, according to ESS Tech. The Oregon-based company says it has attracted more than $1 billion in early-stage customer interest since announcing in late April that it would buy 8.5 GWh of sodium-ion battery cells and modules from Alsym Energy. The system can be configured to deliver 16 hours or more of continuous discharge. ESS Tech spent its first 15 years commercializing iron flow batteries but struggled after going public in 2021, with its stock price falling from nearly $300 per share to less than $1 today.
ESS Tech CEO Drew Buckley said ESS Bridge would "meet the demand we're already seeing" from data centers and utilities while offering a "superior" alternative to lithium-ion batteries. "AI workloads are reshaping what data centers need from energy storage, and sodium-ion handles those power needs more effectively than conventional technologies," Buckley said. The report notes that sodium-ion proponents say the technology is ready to capitalize as utilities and large customers push to secure more capacity on increasingly power- and transmission-constrained U.S. grids.
Sodium-ion batteries offer several advantages over lithium systems, the report explains. They're less prone to thermal runaway, the chain reaction that can cause catastrophic fires like the one that destroyed most of a 300-MW Vistra storage facility near Santa Cruz, California in early 2025. That stability lets sodium batteries operate at virtually any temperature likely to occur on Earth's surface and use simpler air cooling systems instead of the active liquid-based systems that lithium batteries need. Sodium is also cheap and abundant in North America, reducing exposure to Chinese-dominated lithium supply chains and U.S. government restrictions on buying from "foreign entities of concern." But sodium-ion production and installed capacity still lag far behind lithium-based systems, and because elemental sodium is more than three times heavier than lithium, sodium batteries are generally less energy-dense and need a larger footprint to deliver the same capacity.
The sodium-ion market is gaining momentum beyond ESS Tech. Colorado-based Peak Energy said late last year it would deliver up to 4.75 GWh of sodium batteries by 2030 to independent power producer Jupiter Power, and in June announced a 4-GWh manufacturing plant in Sacramento, California to support General Motors' stationary storage plans. The competition suggests sodium-ion technology is moving from niche to mainstream as grid operators and data centers race to add capacity in a power-constrained era.