During last decades, the consciousness about fossil fuels drawbacks emphasized the necessity of radically changing the energy generation paradigm towards the development and diffusion of renewable technologies. Both the gradually depletion of fossil resources and the change in energy generation paradigm make appear really interesting the possibility to couple existing traditional infrastructures with renewable energy systems. This thesis work analyzes the possibility to convert existing offshore Oil&Gas platforms at the end of their operational life, by exploiting their substructures for renewable energy systems installation. The idea to recover and convert offshore platforms seems currently very attractive to the energy community, mainly because it allows to avoid part of the costs associated with the decommissioning phase and to exploit offshore renewable resources in several forms (wind, solar, wave motion).