Solar cells are indispensable to satellites in providing the necessary energy to perform various activities and tasks. As a result, the reliability and durability of solar cells are of great significance to satellite operations. However, as solar cells operate in harsh space environments, they experience continuous performance degradation because the solar cells are exposed to corrosion from atomic oxygen, radiation from protons and electrons, etc. Evaluating the performance degradation of solar cells in space environments is critical for maintaining and utilizing satellites in orbit. This paper proposes a method of modeling solar cell degradation for a resource satellite in orbit based on its telemetry data. First, a double-clustering-based method is proposed to identify the peak currents according to the shape of the solar panel's current data. Then, the peak current is determined as the key parameter for analyzing performance degradation. After that, a degradation model is established based on variations in the solar radiation intensity and solar illumination angle. Finally, the model is utilized to estimate the degradation in solar cell performance on the satellite of interest. Compared with other modeling methods, the proposed method is more applicable for implementation because it relies solely on the output current from the solar cells. Furthermore, it can provide degradation information even when the duration of the telemetry data is limited, i.e., only several months.