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

Abstract

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.

Preliminary method for surveying the state of batteries ageing in isolated PV systems

“…It is also worth noting that a quantitative relation between RMSE and battery capacity decrease should exist. In fact, a 10% increase in RMSE value for each 10% decrease of capacity has been suggested in the original paper [7]. However, we believe our present experimental baggage does not suffice to asses this 2 "Formation" of the plates´ means that the relevant parts of the homogeneous plate materials used in the manufacture of the battery are converted to lead dioxide on the positive electrodes and to sponge lead on the negative electrodes.…”

“…This way effective warning can be established well before lack of energy supply occurs. This proposition, presented in a previous paper [7] was mainly based on theoretical work. This paper presents how an experimental confirmation of this method can be effectively applied to existing monitored PV installations.…”

“…This led us to take into account only this working region to study the batteries' ageing. The preliminary method for evaluating a battery's state of ageing [9] is inspired from the original idea presented in [7]. Whatever the type of evolution the battery is having, standard or anomalous, the passage of time creates a gradual loss of capacity or expected lifespan, intrinsically accompanied by an overall increase in internal resistance.…”

The pierre auger project as a challenging tool to studying PV systems

“…1, we can see the annual distribution of the RF in our system (left). If the system has a deficit less than 1% of the time, it is understood that a well sized system has RF values between 1.08 and 1.20 [6]. Our system is below comfort levels 23% of the times on days with the lowest radiation levels.…”

Ageing estimation for the batteries of the Pierre Auger Observatory

“…The RMSE between two voltage distribution functions on discharge regimen separated in time could be used [3,4] as an estimator of batteries ageing process during this time period, since the modification that the distribution shows as the time runs is translated into a increasing RMSE (see equation (1)) . The RMSE is defined as:…”