Nowadays, there are still some regions in developing countries lacking electrification. A solution to electrify thehouseholds in these areas with off-grid Solar Home Systems (SHS) has been proposed for some time. However,battery storage in SHS is always the limitation in both cost and lifetime point of view. Thus, a battery withstable behaviour, longer lifetime and less maintenance as well as a lower price is highly desired in SHSs. Withthe narrow choices on economical commercial battery technologies, there is another approach to improve thebattery behaviour in SHSs.This thesis is aiming at exploring a solution from usage perspective to maintain the battery behaviour in long-term, in SHSs. In order to achieve the goal, a tool and a method were proposed to provide a practical solutionfor battery performance preservation in SHSs.In this study, two battery technologies which are commonly applied in SHSs were explored: the LiFePO 4battery and the Valve Regulated Lead-acid batteryFirstly, an accurate battery dynamic model based on the electrical equivalent circuit was constructed for bothbattery technologies separately. Series of experiments were performed to obtain the relevant parameters. This model was built for low current applications, which is lower than 1 C, typically suitable for SHS applications.This model was on battery cell level and with a great accuracy with a < 2% errorSecondly, a performance based battery lifetime prediction model was built, and the battery capacity wasselected as the index of the ageing process. The modelling was achieved by applying a new concept, which isthe rate of normalised capacity fading, with respect to capacity throughput. Another series of experiments wereoperated for the exploration of the relationship between stress factors and the rate of battery ageing. Theexperimental data is the foundation of the battery lifetime model.Thirdly, a usage guideline for each battery technology was proposed by analysing the lifetime test data. Thenone practical usage guideline application method was simulated. The application of the usage guideline has anoticeable improvement in the battery behaviour in long term scale.In conclusion, the modelling of the battery including both dynamic behaviour as well as lifetime predictionprovides a tool for future exploration. With this tool, the design and sizing of the battery storage system, as wellas the management of appropriate battery usage in SHS would be easier. The method proposed for batterycapacity preservation is the usage guideline. The usage guidelines offered wide choices on user sideimplementations regarding battery capacity preservation.

The past few years have seen strong growth of solar-based off-grid energy solutions such as Solar Home Systems (SHS) as a means to ameliorate the grave problem of energy poverty. Battery storage is an essential component of SHS. An accurate battery model can play a vital role in SHS design. Knowing the dynamic behaviour of the battery is important for the battery sizing and estimating the battery behaviour for the chosen application at the system design stage. In this paper, an accurate cell level dynamic battery model based on the electrical equivalent circuit is constructed for two battery technologies: the valve regulated lead-acid (VRLA) battery and the LiFePO4 (LFP) battery. Series of experiments were performed to obtain the relevant model parameters. This model is built for low C-rate applications (lower than 0.5 C-rate) as expected in SHS. The model considers the non-linear relation between the state of charge (SOC) and open circuit voltage (VOC) for both technologies. Additionally, the equivalent electrical circuit model for the VRLA battery was improved by including a 2nd order RC pair. The simulated model differs from the experimentally obtained result by less than 2%. This cell level battery model can be potentially scaled to battery pack level with flexible capacity, making the dynamic battery model a useful tool in SHS design.@en