5.3 Flow batteries and sodium-sulfur as emerging alternatives

Beyond lithium-ion

The utility-scale storage market is overwhelmingly lithium-ion today, but other chemistries are active in specific segments and may become more common as the long-duration storage market develops.

Flow batteries — vanadium redox flow batteries are the most commercially mature example — store energy in liquid electrolyte tanks rather than solid cells. The energy capacity is determined by the size of the tanks; the power capacity by the size of the electrochemical stack. This decoupling of power and energy makes flow batteries attractive for long-duration applications where LFP’s physical footprint at 8+ hour duration becomes a significant cost factor. Vanadium flow systems have operating projects in the multi-MWh range and are being deployed in longer-duration applications.

Sodium-sulfur batteries operate at high temperatures and have been deployed at grid scale in Japan and elsewhere, but have not achieved significant penetration in the US utility-scale market. Iron-air batteries and other long-duration technologies are in various stages of commercial development. These are not yet common on the standard utility-scale BESS projects this course focuses on. If you encounter a project with a non-lithium chemistry, the safety protocols, construction requirements, and commissioning procedures will be chemistry-specific. Work from the project documents and the supplier guidance, not from assumptions carried over from lithium-ion projects.