Photovoltaic (PV) plants in Italy are presently subject to a rapid increase due to recent government incentives dedicated to grid connected PV plants. Incentives are given on the basis of the energy actually delivered to the grid, so that it becomes fundamental for the owner to produce as much energy as possible in order to reduce the payback time. In this framework, PV system efficiency plays a fundamental role. This paper focuses on medium and large size PV power systems, for which plant efficiency becomes a key design issue. In particular, the choice between centralized or distributed ("string") architecture is analyzed in terms of plant efficiency, considering the following basic issues: (1) losses in the power electronic conditioning system; (2) losses due to cable dissipation; (3) losses due to possible maximum power point mismatch.
