1. The Key Laboratory of Solar Thermal Energy and Photovoltaic SystemInstitute of Electrical EngineeringChinese Academy of Sciences Beijing 100190 P. R. China
2. University of Chinese Academy of Sciences (UCAS) Beijing 100049 P. R. China
3. State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources School of Renewable EnergyNorth China Electric Power University Beijing 102206 P. R. China