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The Independent Electricity System Operator (IESO) is responsible for operating Ontario’s electricity grid, maintaining system reliability, and administering the province’s wholesale electricity markets.
The IESO coordinates the real-time operation of the power system by balancing supply and demand while ensuring the transmission network operates within physical and reliability constraints.
In addition to real-time system operations, the IESO is responsible for long-term electricity system planning and procuring electricity resources needed to meet future demand.
System Operator
A system operator is an organization responsible for coordinating the operation of the electricity grid, ensuring reliable system performance, and maintaining balance between electricity supply and demand.
In Ontario, this role is performed by the Independent Electricity System Operator (IESO).
⚡ The IESO coordinates both the physical electricity system and the wholesale electricity market.
Operational decisions must satisfy both engineering constraints and market rules.
The IESO operates Ontario’s power system through a control centre that continuously monitors grid conditions.
System operators track:
If supply and demand fall out of balance, operators take corrective action by adjusting generator output or activating other resources.
Real-time system operation occurs on time scales ranging from seconds to minutes.
Generators are dispatched using a process known as security-constrained economic dispatch.
Security-Constrained Dispatch
A dispatch process that selects generation resources to meet electricity demand while ensuring the transmission system operates within reliability limits.
The system operator must consider factors such as:
This ensures that electricity is supplied at the lowest cost while maintaining grid security.
Related topic:
Dispatch
The IESO administers Ontario’s wholesale electricity market.
In this market:
The market provides financial incentives for generators and other participants to supply electricity efficiently.
Related topic:
Electricity Market Overview
In addition to operating the grid, the IESO conducts long-term planning to ensure the electricity system can meet future needs.
Planning activities include:
These assessments inform government decisions about future energy infrastructure.
When new electricity resources are needed, the IESO may administer procurement programs to secure new generation, storage, or demand response resources.
Procurement programs are designed to:
These processes typically involve competitive solicitations for new resources.
The IESO operates within a broader governance framework involving several institutions.
Key relationships include:
These institutions collectively shape how Ontario’s electricity system operates and evolves.
Consider a sudden increase in electricity demand during a summer heat wave.
This coordinated response ensures the electricity system continues operating safely during periods of high demand.
➡ Next Topic:
Electricity Market Overview
This topic explains how Ontario’s wholesale electricity market operates and how market prices are determined.
Last Updated: 2026-03-26