Abstract
The uncertain and variable nature of renewable energy sources in modern power systems raises significant challenges in achieving the dual objective of reliable and economically efficient system operation. To address these challenges, advanced scheduling strategies have evolved during the past years, including the co-optimization of energy and reserves under deterministic or stochastic Unit Commitment (UC) modeling frameworks. This paper presents different deterministic and stochastic day-ahead UC formulations, with focus on the determination, allocation and deployment of reserves. An explicit distinction is proposed between the uncertainty and the variability reserve, capturing the twofold nature of renewable generation. The concept of multi-timing scheduling is proposed and applied in all UC policies, which allows for the optimal procurement of such reserves based on intra-hourly (real-time) intervals, when concurrently optimizing energy and commitments over hourly intervals. The day-ahead scheduling results are tested against different real-time dispatch regimes, with none or limited look-ahead capability, or with the use of the variability reserve, utilizing a modified version of the Greek power system. The results demonstrate the enhanced reliability achieved by applying the multi-timing scheduling concept and explicitly considering the variability reserve, and certain features regarding the allocation and deployment of reserves are discussed.
Highlights
Uncertain and variable conditions associated with increasing renewable generation in modern power systems introduce prominent challenges in the optimal system operation and necessitate the reinforcement of flexible resources to maintain appropriate levels of reliability
This paper presented and evaluated different deterministic and stochastic day-ahead Unit Commitment (UC) policies, with focus on the determination, allocation and deployment of reserves, by making an explicit distinction between the uncertainty and the variability reserve
The main conclusions are: The inclusion of the variability reserve in the day-ahead UC reduces the possibility for ramp shortages and relevant price spikes in Real-Time Dispatch (RTD) and enhances system reliability
Summary
Uncertain and variable conditions associated with increasing renewable generation in modern power systems introduce prominent challenges in the optimal system operation and necessitate the reinforcement of flexible resources to maintain appropriate levels of reliability. The main contributions of this paper are summarized as follows: (a) an explicit distinction is made between the uncertainty and the variability reserve, both falling into the general category of operating reserves; (b) comparable methodologies and mathematical formulations are developed for the DUC and SUC policies, based on the proposed multi-timing scheduling concept, utilizing a detailed modeling of various generating unit operating states; (c) the two-stage SUC policy incorporates the variability reserve extending previous literature, which mainly focuses on the arrangement of renewable generation uncertainty; (d) a specific proposal is made for the quantification of the uncertainty and variability reserve requirements in the DUC policy; and (e) the mathematical formulation of different real-world RTD modes is presented and utilized for evaluating the UC results, instead of interpreting the day-ahead scheduling outcome.
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