Rolling-Horizon Co-Design of Wires and Non-Wires in Distribution Networks.

Distributed Energy Resources (DERs) continues to grow and the regulatory environment evolves to include their participation in new markets, Distribution System Operators (DSOs) must advance their methods for quantifying network hosting capacity and optimizing long-term reinforcement. We present an integrated investment, rolling-horizon planning model that co-optimizes investment in DER technologies (PV, batteries, EVs) and conventional grid upgrades over a 50-year horizon. The formulation is a Mixed-Integer Second-Order Cone Program (MISOCP) built on AC-feasible, convexified branch flow constraints. Solved year by year, the model first optimally allocates DER flexibility to resolve thermal and voltage violations; network reinforcement for lines and substations is triggered endogenously when residual constraints persist (indicating saturation) or the operational lifespan of existing assets concludes. We assess plan robustness across scenarios varying load-growth and technology specific learning rates, utilizing four seasonal peak days for operational chronology. Results, validated on a reduced topology of the IEEE Low-Voltage Test Feeder, reveal a consistent adoption order: PV emerges first, storage is deferred until learning makes diurnal shifting valuable, and reinforcement is triggered where flexibility saturates. Varying learning rates within the optimization process serve as the underlying economic incentives driving the model's multi-decade strategic outcomes; higher rates correlate with a concurrent expansion in the scale of Distributed Energy Resources (DERs) and a proportional increase in substation capacity. This framework presents a highly novel approach to distribution system planning, distinguished by the endogenous timing of infrastructure upgrades a decision triggered by accumulated system constraint violations and necessitated by asset replacement due to end-of-life considerations. The model's decision logic for flexible resources strictly adheres to the operational practices of the Distribution System Operator (DSO), and its rolling planning architecture maintains inter-year feasibility for long-term objectives. Crucially, this comprehensive tool allows DSOs to systematically evaluate the strategic deployment of DERs as a non-wires alternative to traditional infrastructure investment, thereby directly enabling compliance with regulatory mandates, such as the EU Energy Efficiency Directive.