Co-optimising grid reinvestments and reinforcement to support distribution grid planning

The ongoing green transition is driving rapid integration of renewable energy and accelerating electrification across transport, heating, and industry. These shifts result in reinforcement needs for Distribution System Operators (DSOs), which must simultaneously manage ageing infrastructure. This study investigates how reinvestment and reinforcement planning can be co-optimised using a Mixed-Integer Linear Program (MILP). The objective minimises total investment costs while incorporating penalties for cable overloading, extending asset operation lifetime, and premature replacements. Four planning models are developed, reflecting the current investment practice as well as joint coordinated, budget-constrained and reliability-constrained planning approaches. The models are evaluated using 10-kV cable data from the Bornholm distribution network. The results show that simple joint optimisation achieves a 6.2% cost reduction relative to the baseline. The budget-constrained model produces smoother investment profiles but increases the total cost by 1.3%, while reliability constraints reduce the total cost by 5.8%.