Category: ⚡ Markets & Operations
Complexity Level: ●●●○○ (Level 3 – Intermediate)
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Dispatch is the real-time operational process used by the Independent Electricity System Operator (IESO) to determine which generators produce electricity and how much electricity they produce.
Dispatch decisions must simultaneously satisfy:
To accomplish this, the IESO uses a mathematical optimization process that selects generation resources based on both economic offers and system reliability constraints.
Security-Constrained Economic Dispatch (SCED)
A dispatch process that selects generation resources to meet electricity demand at the lowest cost while ensuring that the transmission system operates within reliability limits.
This process ensures that market outcomes remain consistent with the physical capabilities of the power grid.
⚡ Dispatch balances economics and physics.
While generators submit offers based on price, dispatch decisions must also respect the physical limitations of the transmission network and generator capabilities.
Generators participate in dispatch by submitting offers to produce electricity.
An offer typically specifies:
These offers form the supply side of the electricity market.
During dispatch, the system operator evaluates these offers to determine which generators should operate.
The dispatch system uses optimization software to select generation resources.
The objective is generally to:
The optimization considers multiple constraints, including:
The result is a dispatch schedule indicating how much electricity each generator should produce.
Electricity demand and supply conditions change continuously.
To respond to these changes, dispatch decisions are updated frequently.
In Ontario, dispatch calculations occur at regular market intervals, allowing the system operator to adjust generator output as system conditions evolve.
This ensures that the electricity system remains balanced throughout the day.
Dispatch must respect the limits of the transmission network.
For example, a generator may offer electricity at a low price, but transmission limits may prevent that electricity from reaching certain regions.
When transmission constraints occur, dispatch decisions may be adjusted to maintain safe system operation.
Related topic:
Transmission System
Dispatch decisions directly influence electricity market prices.
The price of electricity is typically determined by the marginal generator—the last generator needed to meet demand.
Changes in demand, generator availability, or transmission constraints can therefore affect electricity prices.
Related topic:
Electricity Pricing
Consider a summer afternoon when electricity demand is rising.
Dispatch continues adjusting generator output to maintain balance between supply and demand.
➡ Next Topic:
Electricity Pricing
This topic explains how electricity prices are determined in Ontario’s wholesale electricity market.
Last Updated: 2026-03-26