Distinguish economic dispatch from unit commitment.

Distinguish economic dispatch from unit commitment.

• A. Economic dispatch determines generator outputs to minimize fuel costs given on/off statuses.
• B. Unit commitment determines the operating hours of plants without regard to fuel cost.
• C. Economic dispatch schedules which units to turn on or off over a horizon.
• D. Unit commitment minimizes emissions only.

Answer: (A)

The key idea is the separation between deciding which machines are running and deciding how much each running machine should produce. Unit commitment is the planning step that decides, over a horizon like a day, which generators should be turned on or kept off, taking into account start-up costs, minimum up/down times, and reliability. Economic dispatch comes after that: once the on/off statuses are fixed, it decides the actual output levels of the running units to meet demand at minimum operating cost, considering fuel costs and the units’ limits and constraints. So the best statement captures economic dispatch as the process that sets outputs to minimize fuel cost given the fixed on/off statuses. The other ideas mix in the scheduling aspect or misstate the cost considerations—unit commitment does not ignore fuel costs and is the scheduling stage, not the one that simply minimizes emissions. Economic dispatch does not determine which units to turn on or off over a horizon; that’s the job of unit commitment.

The key idea is the separation between deciding which machines are running and deciding how much each running machine should produce. Unit commitment is the planning step that decides, over a horizon like a day, which generators should be turned on or kept off, taking into account start-up costs, minimum up/down times, and reliability. Economic dispatch comes after that: once the on/off statuses are fixed, it decides the actual output levels of the running units to meet demand at minimum operating cost, considering fuel costs and the units’ limits and constraints.

So the best statement captures economic dispatch as the process that sets outputs to minimize fuel cost given the fixed on/off statuses. The other ideas mix in the scheduling aspect or misstate the cost considerations—unit commitment does not ignore fuel costs and is the scheduling stage, not the one that simply minimizes emissions. Economic dispatch does not determine which units to turn on or off over a horizon; that’s the job of unit commitment.