The invention relates to a heat accumulator for storing thermal energy, comprising a storage container (4) for receiving a storage fluid, which can be stored as a function of the temperature thereof in different, superposed zones (4.1, 4.3, 4.5) of the storage container (4), wherein a heat pump (2) is provided, which is disposed between a lower zone (4.1) and a higher zone (4.3, 4.5) for shifting thermal energy from the lower zone (4.1) into the higher zone (4.3, 4.5). Another object of the invention is a method for shifting thermal energy in a heat accumulator, comprising a storage container (4) for receiving a storage fluid, which can be stored as a function of the temperature thereof in different, superposed zones (4.1, 4.3, 4.5) of the storage container (4), wherein a heat pump (2) delivers thermal energy from a lower zone (4.1) into a higher zone (4.3, 4.5).