A technical perspective on variability costs: Dependence on power variability and cross-correlations

摘要

With power from integrated vRES added to electricity generated by conventional sources across a commitment interval, unexpected real-time changes in demand and generation may contribute substantial overheads to the optimal cost of energy (CoE). This paper presents analytical formulations and illustrative examples to focus on a significant fraction of the cost overheads, commonly referred to as variability costs. By contrast to studies that report a market perspective to the costs, the paper offers a technical perspective through an augmented electricity dispatch, and further takes into account cross-correlations between randomly changing power variables. The minimum CoE across the commitment interval is obtained for the zero variability (maximum likelihood, or ML) demand-generation profile, to which variability costs add as an exclusive linear term, while a similar term accounts for forecast errors and other differentials. Modifications to the CoE that allow extension of the concept to primary-grid/microgrid environment are easily accommodated. Generation schedule examples included in the paper illustrate sensitivity of variability costs to demand variability, vRES generation variability, and cross-correlations. Distinction between central and distributed vRES integration are presented in terms of variability costs as well as overall effect on the CoE.