*Appendix B.2. Battery Sizing*

The use of high-quality components is important as they allow uninterrupted powersupply and the life-span of the components. Although the initial costs of good quality components are higher, their life-time cost is usually limited due to less failures, a longer life-span and higher efficiencies. Batteries are the most expensive component in a solar PV system with storage. The current trend is to move away from the traditional lead acid batteries to lithium-ion batteries. Li-ion batteries have a life-time of 15 to 20 years with an average warranty of 10 years compared to lead-acid batteries which are supposed to have a life-time of 5 years but often create technical problems and die out before this time. Lithium-ion batteries have a higher 80% depth of discharge (DOD) compared to 50% DOD for lead acid batteries. Lithium-ion batteries have a higher efficiency of over 90% compared to lead acid batteries which are 80% efficient. With these factors, life-time costs of lithium batteries are lower than that of lead acid batteries. Additionally, lithium batteries are much lighter and smaller in size. Consequently, Li-ion are the preferred choice in this new configuration of Mpanta MG.

As a second step, the size of the battery has to be optimised. Keeping in view that Mpanta community's ability to pay is very low, only one day battery autonomy can be provided for cost-reasons. This would mean, that the plant would provide power only for 24 h without the sun. Consequently, residents would have a restricted power supply during cloudy days. Further assumed that on average about one third of the load is used during the day, the need of storage is reduced to two thirds of the daily energy output. Taking 80% as the depth of discharge for Li-ion batteries, the required size of the battery system is outlined in the Table below.





\* The system currently only operates 2.15 kW Inverters and 2 charge controllers which probably decreases the actual kWh output of the 45 kWp solar generator by approximately 10–15%. \*\* The lifespan of Li-Ion batteries is approx. 3× longer compared to the AGM/LEAD Batteries that are currently used in Mpanta. \*\*\* The capacity and the charge controllers has been adjusted in the optimised model to ensure maximum output in kWh in relation to the solar generator.
