 Heat pumps can also be used as heat supplier for district heating.Possible heat sources for such applications are sewage water, ambient water (like sea, lake and river water), industrial waste heat, geothermal energy, flue gas, waste heat from district cooling and heat from solar heat storage.In Europe, more than 1500 MW were installed since the 1980s, of which about 1000 MW were in use in Sweden in 2017.