Imperfect Unit Commitment Decisions with Perfect Information: a Real-time Comparison of Energy versus Power

In order to cope with fluctuations and uncertainty, power systems rely on contracted reserves. The day-ahead Unit Commitment (UC) is the short-term planning process which is commonly used to schedule these resources at minimum cost, while operating the system and units within secure technical limits. This paper shows through the evaluation of deterministic cases that conventional energy-based UC formulations lead to inefficient use of reserves in real-time operation to deal with completely known deterministic events. These inefficient decisions are inherent to the assumptions underlying the energy-based formulation, and the misaligned incentives between markets and real-time operation. Economic efficiency and system security can be improved by adopting a UC formulation which explicitly considers the instantaneous power trajectories of generators.