Probabilistic indices for analysing the impact of penetration of distributed energy resources on system reliability

Recent years have seen a steep increase in penetration of renewable energy sources (RES) based generators and storage devices; collectively referred as distributed energy resources (DERs). The traditional reliability indices used by utilities such as loss of load expectation, loss of energy expectation and loss of load probability are suitable for systems with conventional generators. However, they fail to acknowledge stochastic behaviour of RES based generators and energy limited capabilities of storage appropriately. In this study, new probabilistic reliability indices for investigating impact of penetration of DERs on system reliability have been proposed. In order to provide effective assessment, a reliability index referred as expectation of failure in grid connected mode (EFG) and three reliability indices viz. expectation of complete success in islanded mode, expectation of partial failure in islanded mode, expectation of complete failure in islanded mode have been proposed in grid connected mode and islanded mode, respectively. The mathematical formulation for proposed indices has been developed in probabilistic framework. The formulation has been implemented on a 33-bus distribution feeder. Different penetration levels have been investigated to provide adequate justification for proposed indices. Parametric analyses with storage integration have also been carried out. The proposed reliability metrics will assist system planners to choose optimum penetration level with greater efficacy.