Compressed Air Energy Storage (CAES) Efficiency Calculator
Compressed air energy storage (CAES) is one of the few long-duration storage technologies that can hold enormous quantities of energy for hours or days at relatively low cost -- but that capacity comes at the price of round-trip efficiency. This calculator takes the electrical energy used to compress air and a round-trip efficiency figure (auto-filled by CAES system type), then reports the energy recovered on discharge and the energy lost in the process. It pairs naturally with our BESS Round-Trip Efficiency Calculator for a direct efficiency comparison against lithium-ion batteries, and our planned LDES Technology Comparison Calculator for sizing CAES against flow batteries, pumped hydro, and thermal storage.
Selecting a type auto-fills the round-trip efficiency below (still editable). Conventional diabatic CAES is the only commercially proven design at scale; adiabatic and isothermal designs remain earlier in commercialization.
Electrical energy supplied to the CAES system during charging (compression).
Conventional (diabatic) CAES vents the heat generated during compression and burns natural gas to reheat air before expansion, typically achieving only 40-54% round-trip efficiency. Advanced (adiabatic) designs capture and reuse compression heat, reaching 60-70%. Emerging isothermal/near-isothermal designs target 70-80%+ by minimizing heat loss throughout the process.
energy input for compression (MWh) × (round-trip efficiency (%) ÷ 100)
energy input for compression (MWh) − energy output on discharge (MWh)
Results update live as you type. For planning and field-check estimates — always verify against applicable standards and equipment ratings.
How we calculate this →CAES trades round-trip efficiency for massive, low-cost energy capacity. Conventional (diabatic) CAES systems -- the only commercially proven CAES technology at scale, like the McIntosh, Alabama and Huntorf, Germany plants -- lose about half the input energy, delivering only 50 MWh back from 100 MWh in, well below lithium-ion's typical 85-92% round-trip efficiency. But CAES compensates by using underground salt caverns or other geological formations to store enormous quantities of compressed air cheaply, at costs per kWh that can undercut batteries for very long-duration, large-scale applications where efficiency matters less than raw energy capacity and low storage cost.
How CAES efficiency is calculated
This calculator estimates the energy recovered and the energy lost when compressing and later expanding air in a compressed air energy storage (CAES) system, given the electrical energy used to compress the air and the system's round-trip efficiency. Two quantities tie the calculation together.
Energy Output on Discharge (MWh) = Energy Input for Compression (MWh) × (Round-Trip Efficiency (%) ÷ 100). Round-trip efficiency is the share of the charging energy that comes back out as electricity during discharge, after all compression, storage, expansion, and auxiliary losses. At the defaults (100 MWh input and 50% round-trip efficiency), that is 100 × 0.50 = 50 MWh.
Energy Lost (MWh) = Energy Input for Compression (MWh) − Energy Output on Discharge (MWh). The difference between the energy put in and the energy recovered is the energy lost to heat, mechanical, and auxiliary losses across the charge-store-discharge cycle. At the defaults, that is 100 − 50 = 50 MWh.
Two notes on the model. First, the round-trip efficiency figure is the single most consequential input, and it depends heavily on CAES system type: conventional (diabatic) systems vent the heat generated during compression and burn natural gas to reheat the air before expansion, typically achieving only 40-54% round-trip efficiency; advanced (adiabatic) designs capture and reuse the compression heat, reaching 60-70%; emerging isothermal or near-isothermal designs target 70-80%+ by minimizing heat loss throughout the process -- so the system-type dropdown auto-fills a representative efficiency that you can still override with a project-specific value. Second, this calculator isolates the efficiency and energy-loss question and excludes storage capacity, cavern geometry, discharge duration, compressor and turbine sizing, and project economics, all of which matter for real CAES project evaluation. Data sources: CAES technology descriptions and efficiency ranges from NREL (National Renewable Energy Laboratory), DOE (Department of Energy), and IRENA (International Renewable Energy Agency); McIntosh and Huntorf plant specifications from utility and operator documentation; lithium-ion battery round-trip efficiency from industry benchmarks and NREL studies; CAES cost and capacity comparisons from energy storage technology assessments. Verification: with defaults (100 MWh input, Diabatic/50% RTE), Energy Output on Discharge = 50 MWh, Energy Lost = 50 MWh.