A method of storing thermal energy in a body which is in direct thermal contact with the surrounding earth. The energy is transferred to said ground body from heat absorbing devices, specifically solar heat absorbing devices, by circulating a liquid in a circuit incorporating a plurality of channels in the ground body and said heat absorbing devices. The thermal energy stored in the ground body is removed therefrom by means of the circulating liquid and used to control the heat of an object such as a building by circulating the heated liquid around the building in a further circuit incorporating further channels and heat emitting devices. The channels in the ground body are arranged and sized in accordance with the calculated amount of thermal energy supplied to and taken out of the ground body period such as one year. A defined surface surrounding the ground body is established at a distance from the most remote of the channels in a direction outwardly of the ground body so to reach a maximum temperature on the order of 35.degree. C. and a temperature variation during the period of energy input and output of not more than 10.degree. C.