A solar energy system includes a reflecting unit, a heat absorber and a first solar panel. The reflecting unit having a photovoltaic cell with a first energy band gap and a reflecting surface reflects or focuses sunlight. The reflecting unit converts the sunlight with a wavelength shorter than or equal to x nm into electric energy according to the first energy band gap, and reflects or focuses the sunlight with a wavelength longer than x nm onto the heat absorber and the first solar panel. The heat absorber converts the sunlight that has a wavelength longer than or equal to y nm and is reflected by the reflecting unit into thermal energy. The first solar panel having a photovoltaic cell with a second energy band gap converts the sunlight penetrating the heat absorber and having a wavelength shorter than or equal to z nm into electric energy.