Comparative Assessment of Look-Ahead Economic Dispatch and Ramp Products for Grid Flexibility

TL;DR

This paper compares look-ahead economic dispatch and ramp products for grid flexibility, showing their operational differences and limitations under rolling-window operation, and suggests improvements for better performance.

Contribution

It develops linear optimization models demonstrating conditions under which ramp products can match economic dispatch and analyzes their practical differences in stressed conditions.

Findings

LAED achieves similar or lower load shedding than RPs.

Enhanced RP formulation can match LAED at a single time step.

Differences increase under high-load, ramp-limited scenarios.

Abstract

High renewable penetration increases the frequency and magnitude of net-load ramps, stressing real-time flexibility. Two commonly deployed remedies are look-ahead economic dispatch (LAED) and ramp products (RPs), yet their operational equivalence under the industry-standard rolling-window dispatch implementation is not well understood. This paper develops linear optimization models for multi-interval LAED and RP-based co-optimization, and proves that an enhanced RP formulation can match LAED's dispatch feasible region at a single time step when additional intertemporal deliverability constraints are enforced. We then show that this equivalence does not generally persist under rolling-window operation because LAED and RP formulations optimize different intertemporal objectives, leading to divergent end-of-window states. Using different test systems under stressed ramping conditions and multiple load levels, we show LAED achieves similar or lower load shedding than RP implementations with the same look-ahead horizon, with the most pronounced differences under high-load, ramp-limited conditions. The study highlights the limitations of current ramp product implementations and suggests enhancements, such as introducing more mid-duration RPs.