  System operators employ operating reserves to deal with unexpected variations
of demand and generation and guarantee the security of supply. However, they
face new challenges to ensure this mission with the increasing share of
renewable generation. This article focuses on the operational approach adopted
by the French transmission system operator RTE for dynamically sizing the
required margins in the dynamic margin monitoring strategy context. It relies
on continuous forecasts of the main drivers of the uncertainties of the system
imbalance. Four types of forecast errors, assumed to be independent, are
considered in this approach: the errors in the wind and photovoltaic power
generation, production of conventional power units, and electricity
consumption. Then, the required margin is the result of comparing the global
forecast error, computed as the convolution of these independent errors, with a
security of supply criterion. This study presents the results of this method
implemented at RTE and used in real-time operation.
