Abstract: A storage system for heat and cold exchange with a fluid from a solar collector. The system comprises a large block of earth material which is defined at its outer perimeter by a trench. The block of earth material has an outer zone of vertically downwardly extending channels into the block of earth material and an associated inner zone of vertically downwardly extending channels into the block of earth material. Each of the channels holds a conduit for passage of heat exchange fluid to provide heat exchange between the fluid and the block of earth material. The earth is used for storage of heat from a solar collector. The invention also relates to a manner of use of the heat storage system wherein heat which is withdrawn from the system is selectively withdrawn from the outer zone of vertical channels in order to provide more efficient heat withdrawal and storage.