Sizing standalone battery charging systems based on Photovoltaic (PVTCP) Temperature Crossing Points using Voltage Source Photovoltaic Model (VSPVM)

Abstract

Rural and semi-rural communities in third world countries harness solar energy mostly by using standalone Photovoltaic (PV) battery charging systems. Basic electronics circuits that do not include direct current to direct current (DC-DC) voltage converters are employed. These provide raw voltage levels from the solar PV modules that sometimes charge batteries insufficiently, leading to shorter battery lives. By modelling the solar PV module using a voltage source circuit representation, the effects of temperature on the PV module voltage could easily be illustrated to these rudimentary trained communities that deal mostly with voltage sources and not current sources. A Voltage Source PV Model (VSPVM) was developed from the well understood PV cell mathematical model. Microsoft Excel (MSE) was used as the data fitting environment and the PSpice environment was used to capture the electronic circuit topology proposed for the VSPVM. Validating the model against experimental data fitted maximum power points within 5% of the experimental data. Observations made on I-V characteristics plotted on the same graph showed interesting patterns of crossing points referred to here as Photovoltaic Temperature Crossing Points (PVTCP). A low temperature cluster and a high temperature cluster which were indicative of thresholds of some sort were observed. For hot climate regions, the power point voltage which exists between the two clusters could be considered as a guide to the possible range within which a PV battery charging system should operation.