Lead-acid battery lifetime extension in solar home systems under different operating conditions

Abstract

Solar home systems (SHS) provide low-cost electricity access for rural off-grid communities. Batteries are a crucial part of the system, however they are often the first point of failure due to shorter lifetimes. Using field data, this work models the degradation of lead-acid batteries for different SHS use-cases, finding the dominant ageing mechanisms in each case. Corrosion is the dominant ageing mechanisms in all cases apart from the highest use case. This is caused by extended time at high state of charge (SOC) and hence high voltage. A new voltage control scheme is proposed for one of the use cases dominated by corrosion, whereby the number of days between full recharges varies depending on the degradation mechanisms the battery experiences. Simulating the new voltage control scheme yields a 25% increase in battery lifetime whilst ensuring no loss of load to the user.

Figures (6)

• Figure 1: Power flow schematic for BBOXX SHS
• Figure 2: Variation in the corrosion speed parameter with battery temperature and positive electrode voltage.
• Figure 3: Block diagram for the simulation, combining the BBOXX data, Schiffer battery model and proposed voltage control method.
• Figure 4: Simulation results until EOL for high use (blue), moderate use (orange), infrequent use (green) and low use (red) showing total degradation and the breakdown of this into corrosion and active mass degradation.
• Figure 5: Simulation results until EOL for the BBOXX and proposed voltage control methods. The dotted and dashed lines represent capacity loss due to corrosion and active mass degradation respectively.