Abstract: The present invention is primarily directed to a thermal energy storage apparatus for delivering thermal energy to or from a PCM, comprising an elongated heat conducting container (10) having an insertable thermal energy transfer element (15) placed therein, wherein said thermal energy transfer element comprises a plurality of heat transfer paths in the form of transversely disposed flexible heat conducting members (16), at least a portion of which are in contact with the inner wall of said container (10). The invention is also directed to a system using the thermal energy storage apparatus of the invention.