An Analytic Approach to Pay-Back Time Assessment of Grid-Connected PV Plants with ESS

Grid connected photovoltaic plants for residential applications are normally designed through deterministic methods on the basis of system requirements as: PV array peak power, available budget, or available space. Unfortunately, these approaches give only suboptimal results. More effective design techniques are those oriented to fulfill given performance targets as minimum pay-back time, minimum life cycle cost, or minimum annual electrical energy cost. However, they require very complex optimization techniques, especially if the plant encompasses energy storage systems. An analytic approach is presented in this paper to optimally sizing the photovoltaic module array and the energy storage system in a grid-connected generator serving a set of residential loads, on the basis of annual average solar radiation data and load demand. The configuration with the shorter pay-back time is identified through a mathematical model, describing the variation of the annual energy cost as a function of the plant configuration. The proposed method can be easily modified to take into account different optimization targets, as maximum life-cycle profit.