Analytical Degradation-Reserve Sizing of PV–Battery Systems Considering Lifecycle Aging and Service-Equivalent Battery Replacement

This research presents a closed-form degradation-aware sizing framework for PV–battery systems that clearly separates baseline capacity from the additional reserve required for aging. It introduces a service-equivalent comparison between battery reserve and replacement strategies under the same usable-energy requirement. The framework provides analytical expressions for degradation reserve, replacement timing, lifecycle cost, and economic break-even time. Its robustness is further evaluated using an alternative aging model and sensitivity analysis.