Pressurized pumped hydro storage system

An energy or fluid storage system comprising:

• a substrate, said substrate having a substrate central region and, outward of and surrounding said substrate central region, having a substrate surrounding region, said substrate central region having a concave shape when viewed from above, and said substrate surrounding region having a convex shape when viewed from above,
• a bag comprising a deformable boundary defining an interior that can be filled with said fluid and emptied of said fluid as desired, wherein said bag comprises a lower bag layer overlying said substrate in both said substrate central region and said substrate surrounding region and comprises an upper bag layer above said lower bag layer, said bag being capable of occupying a less-filled configuration and a more-filled configuration;
• and
• a mass of overburden overlying said upper bag layer, said mass being able to be raised and lowered as a function of an extent of filling of said interior of said bag,
• wherein said lower bag layer overlying said substrate has substantially identical configuration in both said less-filled configuration and said more-filled configuration,
• wherein said upper bag layer, in said less-full configuration, in an upper bag layer central region, is concave when viewed from above and outward of said upper bag layer central region is convex when viewed from above, and wherein said upper bag layer, in said more-filled configuration, in said upper bag layer central region, is convex when viewed from above,
• wherein said interior of said bag comprises an internal filler piece having a longitudinal direction that at least approximately extends along all or at least a portion of an outer perimeter of said bag,
• wherein said internal filler piece has a cross-sectional shape, said cross-sectional shape being a shape of a cross-section taken perpendicular to said longitudinal direction of said internal filler piece,
• wherein said cross-sectional shape has an outer radius of curvature at an outer-facing portion of said internal filler piece facing said outer perimeter of said bag, and has an inner radius of curvature at an inner-facing portion inward of said outer-facing portion,
• wherein said inner radius of curvature is smaller than said outer radius of curvature, and
• wherein said upper bag layer is unattached to said internal filler piece.