Marginal Network Benefit-Aware Renewable DG Planning in Radial Distribution Systems

High penetration of renewable distributed generation (DG) does not necessarily imply efficient network utilization, because additional installed capacity may provide progressively smaller improvements in distribution-system performance. This paper proposes a marginal network benefit-aware planning framework for renewable DG in radial distribution networks (DNs). The framework combines a Composite Network Benefit (CNB), Marginal Renewable Benefit Index (MRBI), Normalized Marginal Benefit (NMB), and Renewable Benefit Saturation Point (RBSP) to quantify both overall network improvement and the incremental technical value of additional DG capacity. A Benefit-Guided Artificial Bee Colony (BGABC) algorithm is employed to optimize DG locations and capacities subject to voltage, generation, and power-balance constraints. The proposed approach is evaluated on the 33-bus and 69-bus radial distribution systems over renewable penetration levels from 20% to 70% and compared with conventional ABC, PSO, DE, SA, and GWO under consistent simulation conditions. Twenty independent runs are also performed to assess statistical robustness. The results show that active power loss, voltage deviation, and grid-related CO? emissions continue to improve as DG penetration increases, whereas the marginal network benefit declines progressively. The RBSP is identified at 60% penetration for the 33-bus system, corresponding to 2.232 MW of DG, 88.7 kW active power loss, and an NMB of 0.188, and at 70% for the 69-bus system, corresponding to 2.660 MW of DG, 143.8 kW active power loss, and an NMB of 0.105. These results confirm that renewable-benefit saturation is feeder-dependent and that additional DG may remain technically feasible beyond the point where its incremental network value becomes limited. The proposed framework therefore provides a complementary planning criterion for identifying effective DG allocations and technically meaningful renewable penetration levels in radial DNs