YouGen is a web-based social enterprise operated as a limited liability company. It was started in 2008 and aims to provide detailed information on microgeneration technologies, including their suppliers (YouGen 2010). The website helps people find and choose the right renewable energy technologies to purchase. This is achieved by: • Providing research-gathered information from a wide range of sources on renewable technologies; • Providing excerpts on photovoltaic systems from energy experts; • Sharing supplier information and recommendations; • Identifying individuals who have installed a particular technology, and its local suppliers; • Allowing companies to add information about their technology customers. The Energy Saving Trust is a not-for-profit organization that provides free, impartial advice on microgeneration technologies. Energy Saving Trust provides information on the latest emerging microgeneration technologies, the UK's list of suppliers and certified installers. It also provides advice on how to obtain grants, funding and financing options for different microgeneration technology options. Building Researchestablishment is an independent and impartial research, consultancy, testing and training organisation, offering expertise in every aspect 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 prescribers and end users identify products and services that can help reduce their impact on the environment. Green Book Live brings together listings from numerous organizations and provides comprehensive information on "green" products and services... middle of paper... item scenario, the theory and steps are more or less 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 fit the purpose 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 establish the decision problem that the composite index will solve. In decision-making processes a facilitator will meet with decision makers to structure the problem which is often divided into three main parts: the objective (buying a photovoltaic system), the criteria (cost, efficiency, payback period, warranty, etc.) and alternatives (PV1, PV2, etc.). The framework of such a problem is presented in Figure 8.1.