The utility of natural energy, such as solar energy, has been looked over again to secure the energy resources and to keep environment clean. As the solar energy has a defect of the energy density being low, in this paper, the authors tried to improve this defect by the application of reflection sheet with free configuration. Two systems with simple constructions for actual use are discussed here, that is, in the one system, the solar energy is reflected and condensed by the sheet installed on the side wall of building which should be insulated from solar radiation, in the other system, a reflection sheet is set in a green house and the solar radiation in the early spring is reflected by this sheet and absorbed by the soil in this green house. The characteristics of solar energy of both systems are investigated by the theoretical analysis, and are resumed by experimental test in the case of latter system. It is cleared that those systems are useful.