Abstract: An underground heat accumulator of the low temperature type for storing solar energy from a solar collector (8) by means of a plurality of buried double pipes with an outer pipe (3) and an inner pipe (5) has said pipes conically disposed, extending from a central well (1) with a cover (2) near the surface of the ground.The conical position of the pipes provides a very small area in the surface of the ground while embracing a large volume of earth in the depth.The loss of heat at the surface of the ground is therefore limited and yet the accumulation capability is adequate.