Probabilistic Flexibility Evaluation for Power System Planning Considering Its Association With Renewable Power Curtailment

Taking advantage of various flexible resources to reduce or even eliminate renewable energy (RE) curtailment is an important issue in the operational planning of future power systems. Building a highly compatible flexibility evaluation method that incorporates a clear relation between flexibility indices and RE curtailment is crucial to addressing this issue. A novel flexibility evaluation methodology is proposed based on the probabilistic distribution of flexibility adequacy. The novel indices can reflect the direction, amount, frequency, and consequence of lack of flexibility and also have a linear relationship with RE curtailment, features that are beneficial for planners aiming to determine the type of flexible resources needed and to quantify their capacity. The conditional probability distribution functions of different types of flexible resources are first built. Then, a unified form of flexibility on different time-scales is proposed to represent and calculate their contributions to flexible indices using conditional probability convolution. The evaluation method is validated in a combined heat-and-electricity supply system. Four types of flexible resources are studied to demonstrate the quantitative capability of the proposed method in planning, including conventional units, electricity storage devices, heat storage devices, and electric boilers.