The battery voltage distribution: a possible tool for surveying the state of health of stand-alone PV systems

Degradation phenomena can remain unnoticed over long periods in stand-alone PV systems, before eventually causing service interruption. Problems include battery capacity reduction because of ageing, PV array capacity reduction because of wiring corrosion or excessive dirtiness, and mis-adjustment of controller set-points. This underlines the practical interest of an easily applicable method of early detection, so that preventive measures can be taken in good time. This paper proposes the use of the battery voltage distribution, as a tool for surveying the state of health of stand-alone PV systems. Expected distributions can be derived by judicious modelling; while observed distributions can easily be obtained from systematic voltage measurements which are already made in many PV systems worldwide. Comparison between expected and observed distributions allows relatively simple diagnosis rules to be derived. Copyright (c) 2005 John Wiley & Sons, Ltd.