# Compressed-air and CO2 storage

Air or CO2 squeezed into caverns, bags or domes and expanded through turbines later.

Source page: https://www.materialinsights.org/energy/e_caes/

Storage · Mechanical · No. 81

- Storage
- Duration: Hours to days
 Storage · Mechanical · Foundation · Energy

An Alabama plant has stored electricity as squeezed air in a salt cavern since 1991, enough for 26 hours.

Chart: Illustration: Compressed-air and CO2 storage

##### Where it comes from

Chart: Map of where it comes from

Compressors push air into salt caverns or mined caves; newer adiabatic plants keep the heat of compression to reach a design efficiency of 72.1%.

##### Three things to know

1. Older plants waste the heat of squeezing and burn gas to reheat, returning only 29 to 52% of the power.
2. Extra hours are cheap: a 100 MW plant falls from USD 295/kWh at 4 hours to USD 122/kWh at 10 hours.
3. China's Feicheng plant cost about USD 115/kWh (calculated), against about USD 375/kWh reported for California's Willow Rock.

##### The journey

1. 1 **Spare power**Drives compressors when electricity is cheap
2. 2 **Compression**Air heats up as it is squeezed
3. 3 **Heat store**Adiabatic plants keep that heat
4. 4 **Cavern**Salt or rock holds air under pressure
5. 5 **Expansion**Reheated air spins a turbine for power
 Covered in [Storing energy: from fuel stocks to batteriesEnergy](https://www.materialinsights.org/learn/energy/storing-energy/)

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## Other sections

- [Overview](https://www.materialinsights.org/energy/e_caes/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_caes/correlation/index.md)
- [Science and technology](https://www.materialinsights.org/energy/e_caes/sg-sci/index.md)
- [Engineering and performance](https://www.materialinsights.org/energy/e_caes/sg-eng/index.md)
- [Economics](https://www.materialinsights.org/energy/e_caes/sg-econ/index.md)
- [Impact and additionality](https://www.materialinsights.org/energy/e_caes/sg-impact/index.md)
- [What to track](https://www.materialinsights.org/energy/e_caes/tracking/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_caes/links/index.md)