Analyzing operational flexibility of electric power systems

Operational flexibility is an important property of electric power systems and plays a crucial role for the transition of today's power systems, many of them based on fossil fuels, towards power systems that can efficiently accommodate high shares of variable Renewable Energy Sources (RES). The availability of sufficient operational flexibility is a necessary prerequisite for the effective grid integration of large shares of fluctuating power feed-in from variable RES, especially wind power and Photovoltaics (PV). This paper establishes the necessary framework for quantifying and visualizing the technically available operational flexibility of individual power system units and ensembles thereof. Necessary metrics for defining power system operational flexibility, namely the power ramp-rate, power and energy capability of generators, loads and storage devices, are presented. The flexibility properties of different power system unit types, e.g. load, generation and storage units that are non-controllable, curtailable or fully controllable are qualitatively analyzed and compared to each other. Quantitative results and flexibility visualizations are presented for intuitive power system examples. An outlook for the usage of the here proposed methods in power system control centers is given. (C) 2015 Elsevier Ltd. All rights reserved.