PV-Battery Sizing for Stand-Alone Lighting Applications

Abstract

This paper presents a follow-up and addition to a system sizing spreadsheet, detailed in [1], with a focus on sizing or verifying the employability of an off-grid PV-battery system for night lighting. A dimensionless criterion, the Battery Usable Fraction UFbatt is defined, which aids both the calculations of systems and allows an approximate comparison of batteries, regardless of the employed battery chemistry. The outputs from the calculations allow users to rapidly identify whether a chosen or designed system will perform as desired. Further, as it provides a basic temperature-dependent battery capacity model, the influence of ambient conditions can be taken into account. This influence of the ambient conditions is shown to be very important, particularly in cases where the system is designed with little room for error with regards to climatological conditions. Measurements performed indicate that a good approximation for the battery temperature in a PV-battery lighting system is the average of the ambient temperature and the integrated PV module backsheet temperature.