Curtailment

Supply and demand on the grid must always match. The rules call the room to cut generation or raise demand when generation exceeds demand 'downward reserve'. Lowering generator output when this room runs short is curtailment.

When downward reserve falls, or is expected to fall, below the standard level, KPX notifies operators of measures to take, and if that is still not enough it draws up a curtailment plan for non-central-dispatch generators. KPX and the transmission and distribution operators monitor, forecast and control the output of renewable generators, and certain generators must be capable of remote output control. The reliability standard's 'connect first, control later' allows a plant to connect before grid reinforcement on the condition that its output may be curtailed.

News-reading tip: when you read about curtailment, first distinguish whether the cause is a nationwide surplus (a shortage of downward reserve) or a transmission constraint in a particular region. The two call for different solutions.