This document discusses using compressed carbon dioxide (CO2) for alternative energy storage instead of compressed air. CO2 can be liquefied at room temperature at pressures above 67 bar, requiring only 0.2% the volume of gaseous CO2. The system takes advantage of CO2's easy liquefaction by storing energy as liquid, requiring less storage volume than compressed air energy storage. Energy is stored by compressing CO2 into a liquid state ("charging") and recovered by releasing the liquid CO2 as a gas through a turbine ("discharging"). A 4 MWh pilot plant has been completed and a 200 MWh plant is in progress by Energy Dome, but the technology remains experimental and not yet commercially available.

1. Compressed CO2
for alternative
energy storage
MESH 520 - 5.1
Shai Ehrmann
March 31, 2023
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2. Compressed air energy storage (CAES):
● Excess energy used to compress air
● Air compressed and stored in cavern, drained
reservoir, or other large container, typically
● Air heated and released through turbine to
recover energy
● “Battery” similar to pumped hydro storage
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3. Compressed air vs. compressed CO2
● CO2 has a higher critical temperature than the
typical air mixture
○ Can liquefy at room temperature at >67 bar
(>972 psi)
● CO2 in liquid state requires only ~0.2% the
volume of ambient gaseous CO2
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4. LAES<->CAES
● The novel energy storage system takes advantage of the relatively easy liquefaction of CO2, making
it a Liquid Air Energy System
● Energy is stored as a liquid, requiring less volume
● Heat from the compressor is stored or co-cycled to regasify CO2
○ Technically considered an adiabatic CAES(A-CAES/A-LAES) since it does not require external
heat for operation
● CO2 is released into a large gas chamber (i.e. closed loop)
● CAES -> LAES to “charge”; LAES->CAES to “discharge”
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5. Currently only trial by Energy Dome
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6. Considerations
● Can work together with carbon capture, instead of injecting
● Levelized Cost of Storage (LCOS) <$100 per MWh (comparable to Li-ion)
and projected to achieve $50-60/MWh
● Scalable, unlike cavern-based CAES
● Efficiency >75% with heat co-cycle
● 4 MWh/2 MW pilot plant complete, 200 MWh/20 MW plant in progress
● Long-term storage possible
● Still experimental technology
● High pressure system (70 bar+)
● Not market-available, cost unknown but likely high
● Storage capacity limited by bladder size
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7. References
Pacific Northwest National Laboratory. (2019). PNNL: Compressed Air Energy Storage. Caes.pnnl.gov. https://caes.pnnl.gov/
Hydrostor. (2022). Hydrostor Announces Key Milestones for its 500 MW Advanced Compressed Air Energy Storage System in Southern California – Hydrostor. Hydrostor.
https://www.hydrostor.ca/hydrostor-announces-key-milestones-for-its-500-mw-advanced-compressed-air-energy-storage-system-in-southern-california/
EqualOcean. (2022). Zhangjiakou grid connection of the first 100 MW advanced compressed air energy storage project. EqualOcean.
https://equalocean.com/briefing/20220107230110116
Crownhart, C. (2022). This company wants to use carbon dioxide to store renewable power on the grid. MIT Technology Review.
https://www.technologyreview.com/2022/05/03/1051644/carbon-dioxide-storage-energy-dome/
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