Flexibility in a power system: back to basics

In power systems, flexibility can be defined as the ability to cope with variability and uncertainty in generation and demand. In the PhD work of Thomas Heggarty with RTE, and in the frame of the EU H2020 project OSMOSE, we have worked together with Robin Girard and Jean-Yves Bourmaud, to define a formal framework to quantify flexibility requirements and provision.

In a first paper in Applied Energy (link for postprint here) last year, we proposed a method to quantify power systems’ flexibility requirements on different time scales.

The ongoing energy transition, however, is not only affecting how much flexibility is required in a power system, but also who should provide it: some existing solutions are being phased out, while new solutions’ entire business models are based on providing flexibility (e.g. storage or demand response).

I would like to share a second paper that just appeared in Applied Energy and proposes a methodology to quantify power system flexibility provision.

The paper starts with an historical analysis of definitions of power system flexibility, showing that the idea behind the term has evolved with the changing context and perceived challenges. With the intention of condensing information and rationalising debates, a significant number of methods have been proposed to quantify various facets of flexibility. Our paper reviews and classifies them depending on the question they attempt to address.

Figure: Different sources of variability and uncertainty generate a need for flexibility, which can be dealt with by a set of flexibility solutions. These are shown over a range of different timescales.

We then propose a pair of novel tools to quantify a comparatively unexplored aspect of flexibility: who is providing it. These frequency spectrum analysis-based tools separately quantify flexibility provision on the annual, weekly and daily timescales.

Figure: Who currently provides flexibility? Annual (left) and daily (right) flexibility solution modulation stacks, on the French power system in 2018. For data sources, see paper.

The tools’ effectiveness and versatility is demonstrated through several example applications, analysing both historical and prospective power systems, in several geographical locations with contrasting characteristics. For example, we show future flexibility contribution of electric vehicle smart charging and contribution of cross-border trade in highly interconnected systems. The proposed tools are of particular value to the capacity expansion planner, allowing them to quantify changes in flexibility provision as new solutions are introduced, or as carbon taxes, generation and interconnector capacities evolve.

The paper is accessible at: https://bit.ly/3cqgcFO

For a postprint: https://hal.archives-ouvertes.fr/hal-02939532