Glossary
Constraint
Constraint happens where. in order to meet predicted spikes in demand such as the usual 5p.m-7p.m spike, the grid operator constrains down the amount of renewable energy being fed onto the electricty grid in order to allow inflexible thermal plant onto the system and give them sufficient lead in time to “ramp up” its level of generation output.
This means that for a certain period of time before a spike in demand occurs, a certain amount of wind is taken off the system and gradually replaced by plant which will then move towards maximum output. Thus, as the spike occurs, the grid operator is able to “switch on” the wind output it had previously constrained down, as needed allowing it to instantaneously match supply and demand.