System for storing and retrieving thermal energy

A sleeve pipe assembly for a borehole assembly, for use with a thermal collector for heat exchange with the surroundings, comprised of a coaxial collector, the coaxial collector further comprises:

• a flexible material cylindrical sheet, sleeve, for being arranged in a borehole, the sleeve further comprising a top lid and bottom wall, thus providing an air tight environment inside the sleeve,
• an energy carrier and pressurized air/gas inside the coaxial collector such that the outside of the sleeve can be brought in contact with the inside of a borehole wall for optimal heat exchange between the energy carrier and the sub terrain around the borehole,
• an inflow coupling arranged in the top lid and piping for transporting the energy carrier into the coaxial collector, and
• an outflow coupling arranged in the top lid and piping for transporting the energy carrier out of the coaxial collector,
• wherein the top lid further comprises a control valve and piping for filling pressurized air/gas into the coaxial collector and thus controlling the surface of the energy carrier inside coaxial collector, and
• wherein the opening of one of the piping for transporting the energy carrier in or out of the coaxial collector is level adjustable to be adjusted to reach below any set surface level of energy carrier in the coaxial collector.