The planning and appraisal of sustainable energy projects involve rather complex tasks. This is due to the fact that the decision making process is the closing link in the process of analysing and handling different types of information: environmental, technical economic and social. Such information can play a strategic role in steering the decision maker towards one choice instead of another. Some of these variables (technical and economic) can be handled fairly easily by numerical models whilst others, particularly ones relating to environmental impacts, may only be adjudicated qualitatively (subjective or not). In many cases therefore, traditional evaluation methods such as cost-benefit analysis and the main economic and financial indicators (NPV, ROI, IRR etc.) are unable to deal with all the components involved in an environmentally valid energy project. Multi-criteria methods provide a flexible tool that is able to handle and bring together a wide range of variables appraised in different ways and thus offer valid assistance to the decision maker in mapping out the problem. This paper sets out the application of a multi-criteria method (PROMETHEE developed by J.P. Brans et al. 1986) to a real life case that is in tune with the objectives of sustainable development.