Role of storage systems and market based ancillary services in active distribution networks management

The diffusion of Distributed Generation (DG) in MV distribution networks is continuously growing, being supported by the improving performances of small generation units, by the renewable incentives introduced to meet the environmental targets and by the current electrical system liberalisation process. A high DG penetration, however, can be limited by technical factors, especially if consumers and generators are not optimally located and their consumption and generation diagrams are of random and intermittent nature. The network operator will thus have to face some new constraints (e.g. redeployment of power flow along feeders, possible feeder ampacity violations, impact on voltage) which may severely limit the maximum number and size of connectable DG plants, in order to avoid irregular system operations. For the purpose of coping with the electrical grid constraints arising from extensive DG penetration, the adoption of appropriate energy storage systems, together with the introduction of suitable ancillary service markets for promoting user participation to the network regulation, is envisaged to be of crucial importance. Distributors are called to adopt in the next future innovative network controllers to coordinate the operation and the management of their electrical systems and energy storage systems may thus provide interesting features. In this work the feasibility of exploiting storage systems for strategically differing distributed generator and load curves is evaluated, aiming to improve the overall network performance while increasing the level of DG penetration. Issues deriving from the adoption of energy storage systems have been extensively investigated for islanded systems, whereas this work deals with their use in distribution networks, and aims to provide a tool enabling Distributors to easily assess the optimal sizing, siting and managing strategy for grid connected storage systems. The method presented in this paper determines, on the basis of suited preliminary analysis, a reference profile for an ideal storage system and, subsequently, the operation profile for the energy storage system, accounting for its size, capacity and integral operational constraints. Results on a realistic MV system case study are presented and discussed.