A Compressed Air Energy Storage Technology Review

CO2 transcritical systems commercial-refrigeration compressed air energy storage

Compressed air sustained pumped hydraulic storage

Intelligent Utility, March 15, 2016. Image credit: gr8effect

The development of deep water compressed air energy storage (DW CAES) involves placing weight ballasted inflatable bags on the seafloor or submerged on a lake bed, with an air pipe connecting between ground level and submerged bags. It is a variation of water-displacement compressed air storage (WD CAES) that can deliver near constant air pressure throughout the power generation cycle. On a small scale, the line of submerged compressed air can be connected to a large underground water tank capable of holding substantial pressure. The compressed air can raise the equivalent `head’ of the water.

Fluid Density and Mass:

While 100,000-cubic feet of compressed air at 100-psia pressure at 40-deg F would offer a density of 0.53-lb-per-cubic-foot, the total mass available to flow through an engine would be 53,000-lb of air. If compressed air at 100-psia were exerted on 100,000-cubic feet of water, a mass of 6,340,000-lb of water with an equivalent `head’ of up to 230-ft could be available to flow through hydraulic turbines. A suitable cavern to which sealant may be applied to its interior surface inside a coastal mountain could offer the necessary volumetric storage capacity and hold the required air pressure above the water.

Compressed Air over Water:

A dome shaped cavern with 150-feet thickness of granite rock with specific gravity of 2.25 above it could contain an upward push of 14,400-lb-per-square foot, caused by 100-psia on internal air pressure. An internal cavern pressure of 1000-psia would require 1500-ft of granite rock above and around the cavern. The submerged bags of compressed air would be secured at a water depth of 2200 to 2500-ft below water surface to offer such pressure inside a cavern located above water level. A small volume of water under extreme pressure could sustain the operation of a venturi water pump.

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NY State probably doesn’t need to invest as much as people believe in energy storage that’s intended to meet peak demand (catastrophic emergencies are another matter). Around 80% of peak demand is directly correlated with very hot or cold weather. There are already existing, commercially available ADR solutions that can easily slash peak demand by 40-60% 24/7/365 (without advance notice) far cheaper than energy storage and have minimal to no impact on occupant comfort and none on equipment life. If your DR provider doesn’t offer it, then it’s because it’s still using primitive DR approaches that are ineffective, inefficient, and obsolete. Despite what Elon Musk says, the storage cost per kW/kWh/Btu basis to meet peak demand events is almost invariably far too costly – at least in countries that use substantial amounts of space heating/cooling and refrigeration.

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