PURPOSE: To easily install and maintain a solar heat concentrator by a method wherein a heat concentrating bag is provided with a heat concentrating wall, bottom walls hanging from the wall in a spaced relation to define a space and, grip parts formed on both the sides of the bag and the lines for limiting the downward flow direction of a heating medium are formed on the heat concentrating wall.

CONSTITUTION: A heat concentrating bag 1 is provided with a heat concentrating wall 2 for receiving solar heat, a bottom wall 4 hanging from the wall 2 in a spaced relation therefrom to define a space 3 in the bag and bag pulling grip parts 5 formed on both the sides of the bag for use in pulling the bag sideways. The heat concentrating wall 2 is provided on its inner surface with limiting lines 6 for limiting the downward flow direction of a heating medium and the bottom wall is provided with an outlet opening 7 for the heating medium at its lower part. This structure permits the heat concentrator to be spread out into a wide heat concentrating surface by simply exerting tensile force on the bag. This tensile force is exerted on only the heat concentrating wall 2 and the heat concentrating wall can be kept stretched with a small tensile force. Since the bottom wall 4 is used with a freedom of being hung, the load on the bottom wall 4 is small and the solar heat concentrating bag is hardly liable to the trouble caused by the breakage of the bottom wall resulting from wear.