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Electricity systems must continuously maintain a balance between electricity supply and electricity demand.
Supply is provided by generators producing electricity, while demand reflects the electricity consumption of customers across the grid.
Because large-scale electricity storage is limited, system operators must ensure that electricity production matches electricity consumption in real time. Even small imbalances can affect system frequency and threaten grid stability.
In Ontario, maintaining this balance is a core responsibility of the Independent Electricity System Operator (IESO).
Supply and Demand Balance
The condition in which total electricity generation equals total electricity consumption at a given moment, ensuring stable system frequency and reliable grid operation.
⚡ Supply-demand balance is fundamentally a system stability requirement.
When supply and demand diverge, system frequency begins to deviate from its target level (60 Hz).
If not corrected quickly, this can lead to equipment damage or system-wide outages.
Electricity demand varies continuously over time.
Demand patterns are influenced by several factors, including:
For example:
System operators rely on demand forecasting models to anticipate these variations.
Accurate demand forecasts are essential for maintaining system reliability.
Forecasts are developed using:
Forecasts are produced for multiple time horizons, including:
These forecasts help determine which generation resources must be scheduled.
Electricity supply depends on the availability and operating characteristics of generation resources.
Key characteristics include:
Different generation types play different roles in balancing supply and demand.
For example:
Related topic:
Generation Types
The Independent Electricity System Operator (IESO) manages the balance between supply and demand by coordinating generator operations across the grid.
Key responsibilities include:
If demand rises unexpectedly, additional generators may be dispatched.
If demand falls, generation output may be reduced.
Related topic:
Independent Electricity System Operator (IESO)
Ontario’s electricity market plays a key role in maintaining supply-demand balance.
Generators submit offers to supply electricity at different price levels.
The system operator then dispatches the lowest-cost resources needed to meet demand.
This market-based approach helps ensure that electricity is supplied efficiently while maintaining system reliability.
Related topic:
Electricity Market Overview
Consider a winter cold front moving across Ontario.
This coordinated response ensures that supply continues to match demand despite rapidly changing conditions.
➡ Next Topic:
Generation Types
This topic explains how different types of power plants operate and how their technical characteristics influence electricity system operations.
Last Updated: 2026-03-26