Reconstructing Operating Reserve: Flexibility for Sustainable Power Systems

Traditionally, the planning of operating reserve has been done in terms of capacity and average constant ramping requirements, whereas the newly emerging concept of power system flexibility puts emphasis on resources' maneuverability, as well as accurately capturing the intra-hourly variability and uncertainty resulting from significant penetration of renewable power generation. However, the traditional reserve paradigm is deemed impeding to the notion of flexibility, whereas there is yet to be a proper way of defining power system flexibility. To that end, we rethink the fundamental meaning of reserve with respect to the emerging concept of flexibility and present a new flexibility modeling framework. We characterize flexibility provision and flexibility requirements via dynamical envelopes that can reflect the higher order dynamics of power system resources and those of variability and uncertainty. We assert that flexibility adequacy is directly related to how well the aggregate flexibility envelope formed by flexibility resources encloses the flexibility requirement envelope and its dynamics over operational planning horizons. An optimal flexibility planning problem with envelopes is formulated, followed by examples involving unit commitment and economic dispatch.