pressurised fluid storage often referred to as compressed air energy storage represents a very small percentage of the total there has been no obvious acceleration in the rate of invention the converse is true of france both sweden and switzerland have relatively higher counts than is generally found in other fields in terms of technology types active power filtering superconducting transmission lines and flexible ac transmission systems make up almost twothirds of the total claimed priorities figure this is a first and necessary step in determining whether public support for rdd in the area of energy storage and grid management will lead to increased penetration of renewable energy in the grid