In the context of a rapidly growing energy demand and concerns about global climate change, renewable energies and in particular photovoltaic (PV) power are considered long-term solutions towards secured energy supply and for the reduction of greenhouse gas emissions. However, is solar PV a truly sustainable solution? Climate change will certainly not be the only environmental issue we will have to deal with. Regarding the issue of mineral resources, current research efforts aim at reducing raw material consumption in the manufacturing of PV panels. But, how do we assess the environmental efficiency of a panel, especially concerning the raw material consumption? Moreover, the PV industry consumes raw materials which are principally produced in non-EU countries such as Cadmium (Cd), Gallium (Ga) and Indium (In). How do we consider the issue of critical substance and accessibility? Required materials for PV modules may also be used in other applications (for example Gallium and Indium in electrical appliance production). Should competitiveness between applications be taken into account in a sustainability assessment? Are we going to valorize the PV module ability to use substitute substances? In addition to responsible resource management indicators, many other aspects have to be taken into account in order to achieve a complete sustainability assessment, especially recyclability, viability of PV industry, equilibrium along the value chain or social indicators such as social acceptability... Designing sustainability metrics is a new and complex research field. The whole value chain has to be evaluated and all dimensions (environmental, economic, and social) need to be explored. The paper will discuss the issues in defining sustainability metrics and propose some methodologies and a system of indicators to lassess the sustainability of a PV module.