In this paper, a novel image-based concept for estimating solar irradiance received on a photovoltaic (PV) array under normal conditions of irradiance is proposed. The approach is based on the variation of colors intensity in the images of the PV array with respect to solar irradiance. The images of the PV array, which are taken using fixed standard camera and undergo appropriate processing (filtering and intensity averaging), allow the approximation of the instantaneous solar irradiance. The effectiveness of the proposed approach is supported by series of outdoor experimental tests. The results demonstrate that the proposed approach has a good accuracy. As a direct application of the proposed concept, the instantaneous P-V curve of the PV array is approximated using analytical model of the PV array, measured temperature and the estimated irradiance. Once the P-V curve is available, the Maximum Power Point (MPP) can be easily located in real time and then the operating point of the system can be maintained at the MPP.