## 5 Conclusions  
In this paper, the battery sizing and technical assessment of an energy system with a second life energy storage system and an off-grid PV energy system is performed. The main aim of this paper is to investigate the effects of adding extra EV charging station load on the ESS performance applied to a residential building. In addition, a parametric study is performed to assess the SLBs' size variations in the ESS when an extra load is applied. The proposed case study residential building is located in Oxford. This paper has developed a novel methodology for assessing the off-grid PV system stability and minimizing the energy supply-demand mismatch. The proposed off-grid system with second life ESS has been mathematically modelled in MATLAB SIMULINK. The system is simulated considering the worst-case scenario on a day in the middle of winter, when the solar irradiation and demand are at their minimum and maximum levels, respectively. The configuration of the second life ESS is accomplished by utilizing Nissan Leaf retired battery modules with an 80% SoH. The main conclusions drawn from the analysis can be listed as:  
* An increase in SLBs size, when an extra EV charging load is applied, leads to a voltage peak drop in the second life battery. The increase in the number of SLB packs to 4 resulted in a 7.5% voltage peak drop of ESS. Figure 17: The SoC difference in different second life batteries SoHs for various scenarios. * Adding EV charging station demand to the off-grid PV driven system, which has been designed to cover residential building demand (with two second life battery packs), expectedly resulted in instabilities in energy exchange between different components of the system during the year. Assuming that there is no extra space left on the building roof to add PV panels, increasing the number of second life battery packs was explored with the findings suggesting that an installed capacity equivalent to 4 battery packs for the studied residential building would minimize the energy mismatch between the energy supply and demand. This occurs before reaching 2000 discharge cycles and approximately 60% SoH (the final SoC of the ESS increased to nearly 53% for the case with 4 battery packs). * When EVCS load has been applied to the residential load demand, the stability of the system could be improved by increasing the number of second life batteries due to the minimal differences in the initial and final SoC of the second life ESS. This is also beneficial in terms of cost, given that second life batteries have a lower price than brand new batteries. Conceptualization, S.R., D.M., P.H. and A.A.; Formal analysis, F.S. ; Funding acquisition, A.A.; Methodology, S.R., D.M., P.H. and A.A.; Software, F.S. ; Supervision, S.R., D.M., P.H. and A.A.; Validation, F.S. ; Writing--original draft, F.S., S.R., D.M. and P.H. ; Writing--review and editing, F.S. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The related data are presented within the manuscript. * [PERSON] et al. (2021) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Techno-economic and environmental evaluation of grid-connected and off-grid hybrid intermittent power generation systems: A case study of a mild humid subtropical climate zone in China. _Energy_**2021**, _230_, 120728. [CrossRef]
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