Because of the high amount of dust in the Martian atmosphere, solar panels of landers and rovers on Mars get covered by dust in the course of their mission. This accumulation significantly decreases the available power over sols. During some missions, winds were able to blow the dust away. These "dust cleaning events", as they are called, were followed by an increase of the electrical current produced by the solar arrays. However, the Insight Lander solar panels were never cleaned and the mission died of dust accumulation. In order to better predict the evolution of available power produced by solar panels in the Martian conditions, this paper proposes a model of dust accumulation in which the solar flux under the accumulated dust layer is computed taking into account a full radiative transfer in the atmosphere and in the dust layer accumulated on the panel. This work uses several missions observation data to validate this model.