Long-duration energy storage (LDES) refers to technologies capable of storing energy for 10-100+ hours, bridging multi-day gaps in renewable generation. Form Energy's iron-air batteries use reversible rusting to store energy for 100 hours at a fraction of lithium-ion costs. ESS Inc. builds iron flow batteries. Hydrostor develops compressed air energy storage in underground caverns. Multiple DOE-funded demonstration projects are advancing.
LDES is the missing piece for a fully renewable grid. Lithium-ion batteries handle daily cycling (4-8 hours) but are uneconomic for multi-day storage needed during extended weather events — a week of low wind and cloudy skies can drain any battery system. LDES technologies use abundant, cheap materials (iron, air, water) rather than scarce lithium and cobalt.
The DOE's Long Duration Storage Shot initiative targets 90% cost reduction by 2030. Hyperscalers are also investing in LDES to ensure 24/7 clean energy for data centers. The technology is critical for grid stability as renewable penetration increases beyond 50-60%, making it a strategic priority for both climate and energy security.