A heat pump extracts the heat from solar energy stored in the ground or in the air and concentrates it for use in a domestic heating system. It acts like a fridge in reverse. Conventional refrigeration technology absorbs the heat from the ground or air into a refrigerant, which is then compressed to raise its temperature. A heat exchanger then takes out the heat and uses it in the heating system to provide warmth and hot water. Domestic heat pumps have been used in Europe for many years where they are a tried and tested form of high efficiency low cost heating.