Solar cells can be used as coarse sun sensors, and sun vectors can be determined for the entire sky by combining several coarse sun sensors of the same specification. The accuracy of the sun vector is determined based on the on-orbit performance of the coarse sun sensors. On the basis of a large amount of on-orbit data of TZ-1 (TianZhi-1) satellite over an extended period, this study analyzed the angle error between sun vectors determined using coarse sun sensors and differential sun sensor. The output of the coarse sensors was inverted, and the installation angle error and performance attenuation of the coarse sensors were analyzed. The Kelly cosine curve corresponding to the triple junction GaAs solar cell was fitted by combining the output of the multiple coarse sensors. The analysis results show that the installation error of the coarse sensor is slight, the obtained sun vector error is smaller than 5°, and the performance attenuation rate is approximately 0.0621 V/a. The proposed sensor can achieve the all-sky acquisition of the sun vector within a specific accuracy range.