In this paper we present a procedure for the optimal siting and sizing of Energy Storage Systems (ESSs) owned, and directly controlled by network operators of Active Distribution Networks (ADNs). The peculiarity of the proposed planning procedure consists in embedding the grid reconfiguration.We use a recently proposed conditionally exact convex Optimal Power Flow (OPF) as the core of the optimization model. We appropriately model the objective function to include both technical and economic aspects, while keeping the exactness of the relaxed convex OPF. In particular, the proposed procedure accounts for the minimization of: voltage-magnitude deviations, feeders’/lines’ congestion, cost of supplying loads, and investment costs related to the ESSs. In addition, the seasonal configurations of the grid are determined based on (1) network security constraints, and (2) the minimum resistive losses. The stochasticity of loads and renewable productions also are taken into account. We suitably modeled the ESSs to consider their ability to support the network by both active and reactive powers. Two test cases are used to demonstrate, and quantify, the capabilities of the proposed procedure for providing optimal and feasible solutions.