**6. Conclusions**

In this paper, the battery energy storage for 1500 V PV systems was investigated with a comparative reliability analysis of two configurations, i.e., DC-coupling and AC-coupling. The presented analysis can be used to assess how different configurations affect the reliability of the power interfacing units and, thus, justify the selection of configurations for the 1500 V PV-battery systems. With the component-, converter-, and system-level reliability analysis, the most fragile part in each level can be identified, which will contribute to the design-for-reliability of the PV-battery systems with a predictable reliability performance. The presented case study has shown that the AC-coupled

configuration has slightly better reliability performance, whereas the DC-coupled configuration can become more reliable with a proper redundancy design. In all, the exploration in this paper has demonstrated that it is of importance to design for reliability at the system level. Moreover, this can be further extended to examine the overall system cost of 1500 V PV systems during the life-cycle and, then, it will be beneficial to the reduction of the cost of PV energy through design.

**Author Contributions:** Conceptualization, J.H. and Y.Y.; methodology, software, validation, formal analysis, investigation, resources, data curation, writing—original draft preparation, visualization, J.H.; writing—review and editing, supervision, project administration, funding acquisition, Y.Y. and D.V. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Novo Nordisk Fonden through the Interdisciplinary Synergy Programme (Award Ref. No.: NNF18OC0034952).

**Conflicts of Interest:** The authors declare no conflict of interest.
