A model is presented for assessing the global sustainability of power plants. It uses requirement trees, value functions and the analytic hierarchy process. The model consists of 27 parameters and makes it possible to obtain a sustainability index for each conventional or renewable energy plant, throughout its life-cycle. Here the aim is to make society aware of the sustainability level for each type of power system. As a result, decision making can be done with greater objectivity in both the public and private sectors. The model can be useful for engineers, researchers and, in general, decision makers in the energy policy field. With the exception of biomass fuels, the results obtained reinforce the idea that renewable energies make a greater contribution to sustainable development than their conventional counterparts. Renewable energies have a sustainability index that varies between 039 and 0.80; 0 and 1 being the lowest and highest contribution to sustainability, respectively. On the other hand, conventional power plants obtained results that fall between 0.29 and 0.57. High temperature solar-thermal plants, wind farms, photovoltaic solar plants and mini-hydroelectric power plants occupy the first four places, in this order. (C) 2015 Elsevier Ltd. All rights reserved.