Coordination of day-ahead scheduling with a stochastic weekly unit commitment for the efficient scheduling of slow-start thermal units

This paper addresses the problem of the coordination of the day-ahead scheduling with a stochastic weekly unit commitment for the efficient scheduling of slow-start thermal units. The solution of the 24-hour unit commitment may lead to cases, in which slow-start thermal units that are initially offline cannot be scheduled efficiently, due to their long start-up and minimum-up times as well as their large start-up costs. Thus, a new method is proposed, in which the day-ahead scheduling is coordinated with the solution of a weekly unit commitment. The latter is formulated and solved as a two-stage stochastic mixed-integer linear program, under various system and unit operating constraints, according to the provisions of the Greek Grid and Exchange Code. The stochastic parameter of the weekly unit commitment is the unit availability; thus, possible unit outages during the optimization period are taken into account. Test results from the implementation of the proposed method on the medium-scale Greek electricity market are presented.