To meet the varying system load demanded by customers, "dispatchers" decide which generators to run, and at what power level. This decision is made at the system control center, a central point where all the utility's power supply operations are coordinated at all times by the dispatchers.
Throughout the day, the dispatcher "stacks" generators into a predicted and actual load curve. Factors that the dispatcher weighs in deciding which generator to increase or decrease include each generator's:
- cost of operation or "production costs,"
- maximum capacity,
- maintenance schedule,
- environmental emissions,
- and the required reserve needed on the system for reliability.