Nowadays, researchers aim to develop entirely autonomous sensors. By ensuring an important autonomy, the use of batteries solves a part of the energy problem. However, it introduces many problems such as maintenance and environmental pollution. Solar energy harvesting constitutes an attractive solution to provide energy for communicating object. Our objective is to provide an autonomous sensor based on a solar energy harvesting system that can be used in various applications. In this paper we present a new model to perform this characterization. First, the solar panel modeling through the characterization of photo-voltaic solar cell is analyzed. Then, a model to quantify the incident solar energy amount is proposed. In this work, we use a database showing the illumination evolution as a function of time. Furthermore, we present the conversion and storage models of the harvested energy. Finally, solar energy measurements are carried out and validated. The work is realized in collaboration with CEA Tech, CEA Leti and Eolane.