Real-Case Validation of a Weather-Driven Two-Stage Geese V-Formation Algorithm for Distributed Generation Planning and Voltage-Security Assessment in Multi-Feeder Distribution Networks

High penetration of distributed energy resources (DERs) is reshaping radial distribution networks, yet weather-dependent generation, variable demand, and feeder-level surplus–deficit imbalance can compromise voltage quality and coordinated operation. Existing planning approaches often optimize feeders independently and therefore provide limited insight into how local DER portfolios should support inter-feeder energy exchange under time-varying conditions. This study proposes a weather-driven two-stage Geese V-Formation Algorithm (GVFA) framework for planning DER integration and feeder coordination in a practical five-feeder 11 kV Tajeeyaat/North Baghdad system, with complementary validation on a five-instance IEEE 33-bus benchmark cluster. Stage 1 optimizes the siting and sizing of photovoltaic units, wind turbines, battery energy storage systems, capacitor banks, and feeder-specific auxiliary resources using backward/forward-sweep load flow. Stage 2 uses hourly surplus–deficit profiles to select tie-switch configurations and exchange capacities for feeder-to-feeder energy sharing. The framework is evaluated through convergence analysis, optimizer comparison, N-1 contingencies, and seasonal load-growth tests. For the practical system, 24 h aggregate losses decreased from 11,258.1571 to 3367.8481 kWh-eq, corresponding to a 70.0853% reduction. The minimum-voltage range improved from 0.9497–0.9898 to 0.9897–0.9997 p.u., while grid-import reduction reached 94.0270%. For the IEEE-33 cluster, 24 h aggregate losses decreased from 31,746.4712 to 6381.1403 kWh-eq, corresponding to a 79.8997% reduction. The minimum-voltage range improved from 0.8268–0.8632 to 0.9465–0.9683 p.u., while grid-import reduction reached 84.4596%. The framework provides a planning-oriented, sensor-ready decision-support basis for DER siting, voltage-support assessment, grid-import reduction, and candidate inter-feeder exchange corridors.