Distribution expansion planning considering direct effect of flexibility and load priorities

Conventional distribution expansion planning (DEP) involves determining the location, installation time, and sizing of feeders, transformers, and substations in order to have a balance between generation and consumption in planning horizon. In future distribution networks, the penetration of renewable resources will increase. Since these resources are intermittent in nature, it is important to consider methods required to create a balance between generation and consumption in the DEP. In this paper, flexibility, as a key concept in responding to consumption and generation imbalances, is analyzed in the context of DEP. To enable the simultaneous minimization of DEP costs and enhancement of energy flexibility, it is considered as a term in the objective function of DEP. To determine the optimal location and capacity of flexibility resources, load priorities and node self-sufficiency are incorporated into the problem, and a techno-economic analysis is carried out. DEP is studied and evaluated in an 18-bus distribution system using different scenarios for cases with and without considering the flexibility. Two common flexibility resources, energy storage systems (ESS) and distributed generation (DG), are considered as candidates, and sensitivity analysis is conducted. Results of the study showed that DGs are more effective than ESSs for enhancing flexibility. The higher cost of ESS compared to DG was the limiting factor for utilizing ESS, leading to a lower flexibility-to-cost ratio compared to DG.