YouGen is a web-based social enterprise operated as a limited company. It was launched in 2008 and aims to provide detailed information on micro-generation technologies, including their suppliers (YouGen 2010). The website helps individuals find and choose the right renewable energy technologies to purchase. This is achieved by: • Providing research information compiled from a wide range of sources on renewable technologies; • Providing excerpts on photovoltaic systems from energy experts; • Sharing information and supplier recommendations ;• By identifying the people who installed a particular technology and its local environment. suppliers; • Allow companies to add information about their technology customers. The Energy Saving Trust is a not-for-profit organization which provides free, impartial advice on micro-generation technologies. Energy Saving Trust provides information on the latest emerging micro-generation technologies, list of certified suppliers and installers in the UK. Additionally, it provides guidance on how to obtain grants, funding and financing options for different micro-generation technology options. Building Research establishment is an independent and impartial, research-based consultancy, testing and training organization offering expertise in all aspects of the built environment and associated industries. One of its services is the provision of a free online database, Green Book Live, designed to help specifiers and end users identify products and services that can help reduce their impact on the environment. Green Book Live brings together listings from a number of organizations and provides comprehensive information on "green" products and services......midst the paper's scenario, theory and the steps are pretty much the same. In this study, the models developed by Krajnc and Glavič (2005a) and Krajnc and Glavič (2005b) will be adopted and slightly modified to meet the objectives of this study. In the following sections, the mathematical formulations of the methodology are presented. 8.6.1 Mathematical model for calculating the composite index In order to develop the mathematical models for calculating the composite index, it is important to state the decision problem that the composite index will solve. In the decision-making processes, a facilitator will interview the decision-makers to structure the problem which is often divided into three main parts: the objective (purchase a photovoltaic system), the criteria (cost, efficiency, payback time, warranty, etc.) and alternatives (PV1, PV2, etc.). The framework of such a problem is presented in the figure 8.1.