Abstract: A flexible water-impervious roof with a rigid peripheral structure provides support for a plurality of distinct and separate portions of liquid in a system that provides for repeated cycling of heat energy between its roof and its ground reservoir. The flexible roof is formed into a plurality of upwardly open incremental reservoirs which have walls in the form of dimples or tractrices and held in shape by a low-pressure gaseous support. The mechanical system that provides the gaseous roof support also provides the motive force for movement of the thermal energy exchange liquid from the positions thereof wherein energy is absorbed in such liquid to the positions thereof whereat such thermal energy is stored and/or disposed.