A small satellite equipped with a self–developed bus with the high-resolution optical remote sensing instrument(RSI) by integrating NSPO with the ITRC (Instrument Technology Research Center) of NARL was developed under the FORMOSAT-5 satellite program. Solar cell efficiency is temperature related. When the solar panel temperature is over 75℃, the efficiency degrades apparently. FORMOSAT-5 satellite solar power system is compacted due to the limited solar panel sizes at the current configuration.Reducing solar panel temperatures could help increase the availability of generated solar power.The objective of this thermal analysis is to reduce the solar array temperature by thermal control design.The solar panel temperatures with and without radiator under various thermal conditions including different beta angles, summer and winter seasons,solar panel configuration, and operating modes as supplied by electric power subsystem(EPS) designers are calculated.From different case studies, the maximum temperature can be reduced from 103℃ to 94.5℃, or about 8.5℃ for hot condition with radiators applied on the backside of solar panels. This improves the solar panel efficiency for hot condition.