Compressed air energy storage (CAES) power plants are one of the most reliable systems available for energy storage, and they use conventional technology. A salt dome is usually used for the high-pressure air reservoir in the CAES plants currently in commercial operation. However, due to the complicated geological conditions in Japan, it is not easy to design and construct an underground high-pressure air storage tank there. To address this problem, the authors devised a mud slurry lining (MSL) system for storing compressed air underground.

The MSL is a pressurized mud slurry injected into the gap between a reinforced concrete lining and bedrock that provides pre-stress on the lining.

This report outlines the MSL design and considers the two central features affecting practical applications of MSL. The installation conditions are modeled in terms of the rock mechanics under high pressure, and the self-clogging behavior of the mud slurry is discussed with experimental results.

If the maximum pressure is 3 MPa, analysis confirmed that a minimum installation depth of about 100 m is sufficient. Laboratory tests indicate that the critical pressure of the mud slurry is 3 MPa with an artificial joint width of about 3 mm.


Energy storage technology is essential for the widespread adoption of renewable energy generation, because the outputs of solar and wind generation plants tend to fluctuate. Compressed air energy storage (CAES) converts electrical energy into compressed air, and is a promising technology for grids that incorporate fluctuating renewable generation.

Recently the storage efficiency of CAES plants has been improved with the application of effective heat energy storage technology referred to as adiabatic CAES (A-CAES1)).

The concept of A-CAES is diagrammed in Fig. 1. An A-CAES plant can start up quickly and is responsive to load fluctuations. Further, since it only requires conventional equipment, it is highly reliable and has no risk of chemical deterioration.

For A-CAES to be implemented widely, storage capacity must be maximized. Subsurface space is generally used to make the development of a large storage reservoir economically feasible.

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