A Compressed Air Energy Storage Technology Review

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.

Read More