A heat pump circuit has a compressor (C) which compresses a working fluid from a gas in a first state (1) with a low pressure and a low temperature to a gas in a second state (2) with a high pressure and a high temperature, wherein a first subflow of the working fluid is passed in a main circuit (Main) and is condensed into a gaseous/liquid mixture upon passage of a condenser (COND) and assumes a third state (3) by the working fluid delivering heat in the condenser (COND) to a first medium belonging to a heat cycle, and said first subflow of the working fluid is expanded in an evaporator (EVAP) and thereby returns to a gas in the first state (1) by absorbing heat from a second medium in a collector circuit connected to the evaporator (EVAP), whereupon the working fluid is returned to the compressor (C) and completes the cycle again, and wherein a second subflow of the compressed working fluid is expanded from the second state (2) that prevails at the outlet of the compressor (C) and is passed in a converting circuit (Transf) to an energy converter (TG) for converting the energy contents in the second subflow of the working fluid that traverses the energy converter (TG) into electrical energy, whereafter the expanded working fluid from the outlet of the energy converter is returned to the compressor (C) according to any of a) after passage of the evaporator (EVAP) for further expansion, b) directly back to the compressor (C) after expansion in the energy converter (TG) from the second state (2) to the first state (1).