On the Definition and Classification of Power System Flexibility

This paper provides a discussion on the definition and classification of “flexibility” in power systems. The discussion is motivated by a lack of common understanding of what the power system community (including both industry and academia) mean by flexibility. In particular, the paper focuses on three identified issues related to flexibility so far, namely: (i) when defining power system flexibility; (ii) when defining different flexibility services; and (iii) (over)use of the word flexibility without necessarily bringing added value or clarity. We argue that it is of utmost importance that the power system community comes together in the form of, for example, a joint IEEE/CIGRE task force and clearly define power system flexibility and its various aspects (e.g., similar to power system stability). Finally, based on the identified issues and current understanding and use of flexibility in academia and industry, a general classification of power system flexibility is proposed.