There are no discrepancies about the advantages of achieving a sustainable energy system based on locally available natural resources. However, supporters of green energy generation system were lacking some scientific and consistent study to defend their proposals. In order to have such a study, Greenpeace commissioned Technology Research Institute at the Pontificia Comillas University to carry out a study to assess ceilings for the potential and generation of renewable technologies in Spain. It demonstrates firstly a far greater renewable potential than the targets set by long term policies, and secondly, the viability of meeting the entire electricity demand projected for 2050. GIS was used to add the geographical dimension to the original project in order to generate a technical analysis linked to the specific constrictions imposed by territory (natural and anthropogenic) and not just designed to cover a certain demand. Therefore, GIs spatial analysis took into account local conditions producing a more accurate assessment than evaluations made upon "virtual" electrical spaces. This approach could be applied to other small scale general studies in order to assess the maximum contribution of renewable energy sources to particular energy generation mix and to help set development policies supporting high participation of renewable technologies. (C) 2007 Elsevier Ltd. All rights reserved.