The project goal was to assess the viability of photovoltaic (PV) installations in two different existing buildings, both located in the city of Neuchâtel. The two studies buildings were built in 1938 and 1968. Before testing any PV installation, a renovation of the envelope were proposed in order to achieve a high level of energy performance. Indeed, the two buildings require a large amount of energy for heating due mainly to the low performance of the existing envelope. Different scenarios were tested considering the legal requirements in Switzerland (SIA norms). In addition, their cost-effectiveness was assessed. After the implementation of a passive renovation, improving the energy performance of the building envelope, a scenario integrating PV elements on roof and facades was assessed. Different configurations were tested, in order to improve the energy balance on the building taking into account the on-site energy production. Finally, a comparison of the results from both case studies was conducted.