PVSizer: An Open-Source Python Framework for PV and BESS Sizing and Impact Analysis in Distribution Networks

High photovoltaic (PV) penetration in distribution systems may cause voltage violations and thermal overloading, while existing open-source tools do not provide an integrated and automated approach for systematic PV and battery energy storage system (BESS) sizing under feeder constraints. To address this gap, this paper presents PVSizer, an open-source tool for PV-BESS sizing and impact assessment in distribution networks. Built on OpenDSS and a Python-based automation layer, PV Sizer provides three modules: (1) Impact Analysis/Time-Series Simulation for detailed quasi-static time-series (QSTS) analysis of a specified configuration; (2) Traversal for parallel feasible domain mapping under feeder operational constraints; and (3) Optimization based on constraint-guided incremental search (CGIS) to identify the maximum feasible PV capacity together with the minimum required BESS support. Case studies on a real utility feeder with over 700 nodes show strong site dependence in feasible PV-BESS sizing limits. The Optimization module reaches the same final solution as exhaustive Traversal with substantially lower computational burden, demonstrating the usefulness of PVSizer for feeder-constrained PV-BESS integration studies.