Abstract The degree of efficiency of Building Integrated Photovoltaic (BIPV) as a shading device and the variation of the electrical power generation over 1 year in a real building has already been experimentally investigated in my earlier research. In this paper, the influence of the angle of the solar cell panel, albedo of earth, building azimuth, and of solar cell panels under shading on the power generation are theoretically studied to further optimize BIPV implementation. For the validation of the theoretical work, experimental results of the Samsung Institute of Engineering and Construction Company building are used with a wind velocity of the weather data (TRY, test reference year) of Suwon area, Korea. The efficiency of the BIPV system as a shading device was compared at different months. In this work, the simulation program SOLCEL, for the calculation of a shading/sunlit area on solar cell module and facade, surface temperature of solar cell module, effective solar irradiance on solar cell module and the power generation of a BIPV as a shading device, was developed and validated. The SOLCEL can be applied to develop a multi functional Building Integrated Photovoltaic which could improve power generation, thermal comfort, natural lighting, cooling and heating, etc.