Electricity Facts

Key statistics about Ontario’s electricity system, electricity marketplace and programs and initiatives delivered by the IESO. All values have been rounded.

Electricity Use

  • 5.3 million electricity customers in Ontario – including 4.8 million residential customers - in 2020
  • 128.2 million MWh of electricity delivered to customers in 2020
  • 22,428 MW highest summer peak demand in 2021 (set on August 24)
    • 27,005 MW all-time highest summer peak demand (set on August 1, 2006)
  • 20,455 MW highest winter peak demand in 2021 (set on December 7)
    • 24,979 MW all-time highest winter peak demand – set on December 20, 2004

Data Sources: Number of customers and electricity delivered data drawn from the OEB Yearbook. Peak demand data drawn from the Data Directory: Hourly Demand Report.

Energy Efficiency

  • 250,000 homes and businesses have benefitted from Save on Energy programs since 2011 (Source: Save on Energy)
  • 16 TWh reduction in electricity use as a result of energy efficiency and conservation initiatives since 2011 – enough to power 1.7 million homes for one year
  • 220,000 energy efficiency projects undertaken by business customers to lower their costs and improve their operations

Data Source: Save on Energy

Save on Energy logo with slogan Power What's Next

Save on Energy

Through Save on Energy, the IESO offers programs and incentives to help individuals and businesses use energy more wisely. Discover your energy-saving potential by visiting the Save on Energy website.

Resource Mix

Transmission-Connected Capacity

Capacity is a measure of how much electricity Ontario's system can produce at any given time. As of September 2022, Ontario's transmission-connected capacity was over 38,000 MW.

Transmission-Connected Capacity as of June 20, 2024 (Source: Reliability Outlook)

Electricity System Output

Output is the actual amount of electricity that is produced and delivered to customers. In 2021, Ontario's electricity system produced more than 142 TWh of electricity.

Ontario’s electricity output by source in 2021 broken down as: Nuclear = 83 TWh or 58%, Natural Gas/Oil = 12.2 TWh or 8.6%, Hydro = 34.2 TWh or 24%, Wind = 12 TWh or 8.4%, Biofuel = 0.4 TWh or less than 1% and Solar = 0.75 TWh or less than 1 %.

Electricity Output by Fuel Type in 2021 (Source: Year End Data)


  • 30,000 km of high-voltage transmission lines running through Ontario

    (Source: Ontario Systems Map)

  • Intertie connections with 5 neighbouring jurisdictions linking Ontario’s electricity grid with Manitoba, Quebec, Michigan, Minnesota and New York

Electricity Market

Community and Stakeholder Engagement

  • More than 3,000 registered members to Ontario’s regional electricity networks.
  • 21 electricity planning regions, nine of which were undergoing active planning cycles in 2021

Helpful Tools | Electricity Facts and Tools

This collection of maps and online tools can help you understand and navigate Ontario’s electricity system.