Loss-of-load probability and related parameters in optimum computer-aided design of stand-alone photovoltaic systems

Abstract

Loss-of-load probability (LOLP) and related parameters are presented as a technique, based on an hour-by-hour approach, for optimum computer-aided design of stand-alone photovoltaic (PV) systems. The minimum, and hence economically optimum, size of a PV system of a specified degree of reliability is determined mathematically as a function of the array orientation. Also, the dependence of unserved energy (as a measure complementary to LOLP) on array tilt angle and/or orientation for a given PV system is determined. The technique is applied in the design of a stand-alone PV system in a remote and isolated village in northern Greece. For a given array orientation, the optimum array tilt angle (which minimizes the size of the PV system) is independent of the chosen values of LOLP. The unserved energy increases linearly with array area for a given battery capacity, decreases with increasing battery capacity and array off-south orientation, and increases with increasing values of LOLP. The minimum values of unserved energy for a given battery capacity and a given orientation correspond to the optimum array tilt angle. The dependence on LOLP of the total life-cycle cost (TLC) of a PV system having the optimum size for the desired degree of reliability, for a range of LOLP values comparable to the range of reliability levels of traditional systems, is rather weak. The TLC of an optimum system increases with array off-south orientation, particularly for angles greater than ±30°.