Ensuring reliability of FCR and aFRR provided by wind & solar

Transmission System Operators (TSO) must ensure system stability, both today and considering future developments. As Wind and Solar generation increases in the energy mix, renewable energy producers must increasingly contribute to system flexibility and security. In France, for example, large Wind and Solar power plants are currently required to have the capability of providing automatic frequency control, FCR and aFRR. To do so, Wind and Solar power plants must operate below their maximum operating point, Pavailable(t). The main issue here is that, when those assets are operated below their optimum operating point, the value of Pavailable(t) can no longer be measured and must be estimated. This estimated optimal operating point is then used to determine the power setpoint for the power plant, including the power margin for FCR and aFRR. Inaccurate setpoint computation may result in insufficient delivery or availability of the reserve on the asset. This paper aims to illustrate this issue through a statistical study of lab data, notably assessing the impact on French reserves if no actions are taken to correct the estimations errors in Pavailable(t). Then, it presents the solutions that RTE, the French TSO, is considering securing its reserves.