Ontario Electricity Explained Ontario • Electricity
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Ontario Electricity System Explained – Complete Guide

Updated 2026‑04‑22

Ontario’s electricity system is one of the most complex pieces of infrastructure in the province. It spans massive nuclear stations, hydroelectric dams, wind farms, solar installations, natural gas plants, transmission towers, local distribution networks, and a real‑time market operated by the Independent Electricity System Operator (IESO). Yet for most households, the system is invisible — until the monthly hydro bill arrives.

This guide explains how Ontario’s electricity system works from end to end. It covers generation, transmission, distribution, regulation, pricing, and the market structure that determines how electricity is bought and sold. By understanding how the system operates, you can better interpret your bill, understand rate changes, and see how Ontario plans for future electricity needs.

1. The big picture: how electricity flows in Ontario

Ontario’s electricity system has four major layers:

  1. Generation — power plants that produce electricity.
  2. Transmission — high‑voltage lines that move electricity across the province.
  3. Distribution — local utilities that deliver electricity to homes and businesses.
  4. Regulation and market operations — organizations that set rules, run the market, and ensure reliability.

Electricity is generated at power plants, transmitted long distances at high voltage, stepped down at substations, and finally delivered to your home through local distribution networks. Every part of this chain adds cost, which is why your bill includes multiple line items.

2. Ontario’s electricity generation mix

Ontario uses a diverse mix of electricity sources to ensure reliability and reduce emissions. The main categories are:

Nuclear

Nuclear power provides more than half of Ontario’s electricity. It runs continuously and forms the backbone of the system. Nuclear plants have high upfront costs but low operating costs, making them ideal for baseload power.

Hydroelectric

Hydro stations provide renewable, flexible power. They can ramp up quickly to meet demand spikes and help balance the system. Ontario has both large hydroelectric dams and smaller run‑of‑river facilities.

Natural gas

Gas plants are used mainly for peak demand and reliability. They can start quickly and provide backup when renewable output is low or when demand is unusually high.

Wind and solar

Wind and solar generation depend on weather conditions. They reduce emissions and fuel costs but require backup from other sources when output fluctuates.

Bioenergy and other sources

Ontario also uses biomass, landfill gas, and other small generators to support the grid.

This diverse mix helps Ontario maintain reliability while managing costs and environmental goals.

3. How electricity is transmitted across the province

Once electricity is generated, it travels through the high‑voltage transmission system operated by Hydro One and a few smaller transmitters. These lines move electricity from power plants to regional substations.

Transmission lines operate at very high voltages — often 230 kV or 500 kV — to reduce energy loss over long distances. At substations, transformers reduce the voltage so it can be delivered safely through local distribution networks.

Transmission charges on your bill help pay for this infrastructure.

4. Local distribution: how electricity reaches your home

Local distribution companies (LDCs) deliver electricity from substations to homes and businesses. Examples include:

  • Hydro One
  • Alectra Utilities
  • Toronto Hydro
  • Elexicon Energy
  • London Hydro
  • Ottawa Hydro

Distribution networks include poles, wires, transformers, meters, and maintenance crews. These costs appear on your bill as delivery charges, which include both fixed and variable components.

5. The IESO: operating the grid and running the market

The Independent Electricity System Operator (IESO) is responsible for:

  • balancing supply and demand in real time
  • running the wholesale electricity market
  • planning for future electricity needs
  • managing long‑term contracts and reliability programs

The IESO ensures that electricity supply always matches demand — second by second — across the entire province. It also operates the market where generators are paid for the electricity they produce.

6. How the wholesale electricity market works

Ontario uses a competitive wholesale market where generators submit offers to supply electricity. Every five minutes, the IESO calculates the price needed to meet demand. This is called the HOEP (Hourly Ontario Energy Price).

However, most generators are paid through long‑term contracts or regulated rates. The difference between the market price and contracted/regulated costs is recovered through the Global Adjustment.

This is why residential customers pay regulated rates (TOU, Tiered, ULO) rather than the HOEP directly.

7. The Ontario Energy Board (OEB): regulating prices and utilities

The OEB regulates electricity rates, approves utility budgets, and sets the rules for billing and consumer protection. It determines:

  • TOU, Tiered, and ULO electricity prices
  • delivery charges for each utility
  • rules for disconnections, billing, and customer service

While the IESO runs the market, the OEB ensures that residential customers pay fair, regulated prices.

8. Imports, exports, and interconnections

Ontario is connected to neighbouring electricity systems in Quebec, Manitoba, Michigan, New York, and Minnesota. These connections allow Ontario to:

  • import power when it is cheaper elsewhere
  • export surplus power when Ontario has excess supply
  • improve reliability through shared resources

Imports and exports help stabilize the system and reduce overall costs.

9. Why electricity prices change

Electricity prices in Ontario shift over time due to:

  • fuel costs — especially natural gas
  • weather — extreme heat or cold increases demand
  • contracted supply — long‑term contracts influence GA
  • system upgrades — refurbishments and new infrastructure
  • market conditions — supply and demand affect HOEP

These factors combine to shape the regulated rates paid by households.

10. The future of Ontario’s electricity system

Ontario is preparing for major changes in electricity demand and supply. Key trends include:

  • growth in electric vehicles
  • electrification of heating and industry
  • new nuclear projects and refurbishments
  • expansion of energy storage
  • more renewable generation
  • modernized market rules

The IESO’s long‑term planning documents outline how Ontario expects to meet rising demand while maintaining reliability and managing costs.

11. Why understanding the system matters

Electricity touches every part of daily life, from heating and cooling to appliances, lighting, and transportation. By understanding how Ontario’s electricity system works, you can:

  • interpret your hydro bill more clearly
  • understand why rates change
  • make informed decisions about pricing plans
  • see how provincial energy policies affect long‑term costs

This guide is educational and intended to help Ontario residents understand the system that powers their homes. For official information, always consult the Ontario Energy Board, the IESO, and your local utility.