Physics / mechanism
Compressed-air energy storage (CAES) uses off-peak electricity to compress air into underground caverns (salt, aquifer, depleted reservoir) or pressure vessels, then releases it through a turbine to regenerate electricity. Two commercial plants exist: Huntorf (290 MW, Germany, 1978) and McIntosh (110 MW, Alabama, 1991) — both diabatic, burning natural gas to reheat expanding air, yielding ~42–54% round-trip efficiency (RTE). Advanced adiabatic CAES (AA-CAES) captures compression heat in thermal storage and reuses it on expansion, targeting 70%+ RTE; no commercial AA-CAES plant operates yet. Isothermal CAES (liquid-piston, near-ambient temperature) targets 75–80% RTE at smaller scale. Storage duration is 4–24+ hours; cost projections sit around $100–200/kWh installed for cavern-based systems.
Competitive landscape
Pumped hydro dominates long-duration storage (>90% of installed grid storage capacity). Lithium-ion dominates 2–4 hour discharge but degrades on deep cycling. Flow batteries (vanadium, iron-air) compete at 6–12 hours with location independence. Gravity storage (Energy Vault) and liquid-air (Highview Power) occupy similar geological-independence niches. CAES differentiates on cavern geology dependency but wins on capex at large scale and multi-day duration potential.
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.