Cycling and flexibility concerns revealed in high variability systems employing sub-hourly UC

As the level of renewable generation on the power system increases, so too does the uncertainty and variability it introduces. It may no longer be appropriate to schedule units at an hourly resolution as the system´s sub-hourly variability and uncertainty may be underestimated. This paper examines if a sub-hourly unit commitment model is applicable for systems with high variability compared to the traditional hourly time-step. A mixed-integer programming unit commitment formulation with a user selected time-step is implemented with new unit states defined, modifications to traditional constraints, and additional constraints to account for operational procedures previously ignored in an hourly context. For three increasing wind penetration scenarios, sub-hourly modeling reveals higher levels of unit cycling and a reduction in system flexibility compared to an hourly resolution, which can lead to an increase in system costs, and a reduction in life expectancy and efficiency for generators.