This study quantitatively assesses the life-cycle environmental impacts of 1 m<^>2 of Si and CdTe Photovoltaic module. GaBi LCA software is applied to establish the LCA model and to perform the calculation, and CML 2001 baseline method is chosen to quantify the environmental impacts. The comparative analysis shows that CdTe technology requires less energy and material resources than Si technology resulting in a reduction of all impacts related to polluting emissions and to material resources consumption. Instead, the human, aquatic and terrestrial toxicity environmental impacts are particularly high for the CdTe panels because they are made of toxic materials. The study highlights the importance of the recycling process at the end of life which involves the recovering of raw materials, a decrease of energy demand and a reduction of emissions of materials that would be harmful to the environment if discharged in landfills. The analysis finally shows the sustainability of these photovoltaic systems through the evaluation of EPBT indicator. The energy pay-back time was calculated carrying out a parametric analysis, varying the main variables, and providing a framework as detailed as possible of the results obtained. (C) 2017 Elsevier Ltd. All rights reserved.