The universal design of roof photovoltaic (PV) systems in substations often neglects specific roof resources and regional irradiance characteristics

which frequently leads to capacity waste. To address this issue

this paper focuses on 220 kV fully indoor substations to study the optimal capacity configuration of roof PV systems. Based on a survey of PV construction data across multiple provinces

the characteristics of roof resources and the current status of PV configurations are analyzed. Furthermore

the principles for module selection

array design

and layout are clarified. A PV output power model incorporating inclined-plane irradiance and module operating temperature is constructed

and typical PV output scenarios are generated using the K-medoids clustering algorithm. With the objective of maximizing comprehensive economic benefits over the entire life cycle

an optimal configuration model is established

integrating constraints on spatial limits

power balance

and anti-backfeeding. Finally

a 220 kV fully indoor substation in Jiangsu is taken as a case study to determine the optimal configured capacity. The proposed method provides a valuable reference for the PV capacity configuration of different substations

effectively improving design rationality and economic benefits.