Evaluating reactive power reserves scarcity during the energy transition toward 100% renewable supply

The energy transition toward renewable-dominated electricity supply, which many countries committed to achieve in the next decades, will pose major challenges to power systems reliable operation. A significant anticipated challenge, yet not tackled quantitatively by research works, is that, if countermeasures are not planned, the transmission grid will likely face in the years to come extreme situations of lack and/or excess of reactive power. This paper first raises awareness on the key issue of reactive power reserves scarcity as one moves toward renewable-dominated electricity supply and brings quantitative evidence underpinning this issue. Then, the paper elaborates a crude first version of a methodology to predict when such issue may start to occur. The core of the methodology includes a tailored AC security-constrained optimal power flow (SCOPF) problem which evaluates the reactive power reserves scarcity. The usefulness of the proposed methodology is illustrated on two systems of 5 and 60 buses, respectively, considering N - 1 contingencies.