A supply-demand imbalance is considered to exist when RTE generates one or more messages about insufficient offers on the balancing mechanism (alerts or degraded modes) to encourage participants to submit additional offers.
The number of instances where supply was tight on the balancing mechanism (i.e. where demand exceeded supply) was comparable to 2018, at 63 half-days. The factors that can cause such imbalances include social movements at generation plants, heatwaves, environmental constraints and cold spells. The month of December alone, when significant social movements occurred, accounted for 23 half-days.
The number of instances of tight situations due to supply exceeding demand increased to 14 half-days (see box below, For a better understanding).
Tight situations due to excess supply
It is easy to imagine tight situations arising when electricity demand exceeds supply, but the transmission system can also find itself in a tight situation due to surplus supply, when demand is low (decline in activity due to holidays, weekends or bank holidays). These situations occur more often in summer, when consumption is lower, but also on weekends in the spring, particularly when wind and solar output are high and consumption is low in Europe.
In these instances, France may need to export large quantities of energy to avoid finding itself with too much supply. When the limits of export capacity are reached, RTE may request that generating units reduce or stop their production temporarily. Because wind and solar generation are given priority, fossil-fired thermal and nuclear generation in particular may decrease sharply.
Instances of surplus generation have been occurring more frequently in recent years, notably because of the continued development of renewable energy sources and the increase in minimum production requirements for nuclear reactors (technical constraints declared by the plant operators).