The energy payback performance of an energy generating technology such as PV, is usually based on a single system considering static parameters for its evaluation. However it is recognized that performances of an installed systems decrease over time, while, on the other hand, the performances of new systems is expected to slightly increase over time. Additionally the energy required for manufacturing a new system has decreased significantly in the last years and additional decrease is expected in the near future; moreover the opportunity to recycle materials from dismantled PV installations is becoming massively investigated and some technologies are already on industrial scale. These dynamic aspects inspired the present work that firstly consider the calculation of the energy payback of PV systems that should drive the most sustainable decision regarding the optimal timing for dismissing of an old PV system and replacement with a new one.