Starting from the results of a life cycle assessment of solar thermal collector for sanitary warm water, an energy balance between the employed energy during the collector life cycle and the energy saved thanks to the collector use has been investigated. A sensitivity analysis for estimating the effects of the chosen methods and data on the outcome of the study was carried out. Uncertainties due to the eco-profile of input materials and the initial assumptions have been analysed. Since the study is concerned with a renewable energy system, attention has been focused on the energy indexes and in particular the "global energy consumption". Following the principles of Kyoto Protocol, the variations of CO2 emissions have also been studied. (C) 2004 Elsevier Ltd. All rights reserved.