In this paper, an autonomous photovoltaic system is going to be designed for the North Tower of Instituto Superior Técnico through the application of solar panels on its windows, using them as producers of electricity based on solar energy. The main objectives of this paper are: (1) to make the building energetically autonomous, using an integrated system of solar photovoltaic technology; (2) check the system behaviour and comment on possible system impacts on the user’s lifestyle. Two solutions are going to be proposed to cover/substitute the windows of the Tower, one using amorphous silicon panels and the other using crystalline silicon panels. Taking into account this type of solution, it is possible to recognize that there are positive impacts, such as the reduction of transmission lines/grids or the decentralisation of energy supplies. However, there are also disadvantages such as the need to have an energy storage system to guarantee the continuous supply. This study, for this building in particular, shows that organic photovoltaic cells have enormous advantages in the future in terms of our environment and social needs, but they do not yet produce the energy needed to meet today’s needs. Both solutions present a return estimative time of seven years, with an initial investment of approximately two million euros, but the produced energy will not be enough to create an off-grid system.