to fig1 and 2 the hot water tank consists in essence of a housing 1 preferably made from steel sheet metal which is surrounded by an endless insulating casing 13 the insulation casing 13 is made in known fashion e g from insulating material which is surrounded by either a plastic or a sheet metal casing it is important that the housing 1 can be made from relatively cheap sheet metal which can be processed using simple bending methods and that the housing 1 in the front view fig1 and in the top view fig2 is shaped essentially rectangularly the manufacturing cost of such a housing is therefore low it is self evident however that the housing 1 could also be made round or be shaped otherwise according to the present general description it is also intended that the housing 1 is made as a heat accumulator and there it is intended that the housing 1 is completely filled with a liquid 2 the liquid 2 could be either water or a water coolant mixture or the like the figures also illustrate an enclosure 3 farming a chamber integrated into the heat accumulator in which the units of the combined heat and power generator are located these units are essentially the internal combustion engine.