What’s in Ontario’s Electricity Supply Mix

This Matters if You Are: interested in learning about the resources that power Ontario’s electricity system, and the role each resource plays in ensuring reliability. Here you’ll find:


Ontario’s electricity supply is made up of a diverse set of energy resources, including nuclear, hydro, wind, solar, biofuel and gas. Understanding how each of these resources work to ensure a reliable supply of electricity, can provide insight into the value of each resource in our supply mix, and the important role communities play as hosts for new and existing generation facilities.  

Across the province are generation facilities for these resources. Ontario’s diversity in energy resources strengthens the reliability of Ontario’s power system as different resources serve different functions.

No single energy resource can meet all of our system needs at all times. Maintaining a diverse supply mix, where the different resources are complementary to each other, is an effective way to provide the services necessary to balance the supply and demand of electricity and maintain the reliability of Ontario’s power system.

Sources of generation are evolving, as are the province’s supply needs. As distributed energy resources and new technologies help to meet needs at the local level, the IESO must adapt and work alongside communities to effectively coordinate with these new resources.

Breakdown of Ontario’s Supply MixPie Chart showing a breakdown of Ontario's Electricity Supply Mix

Source: IESO’s 2020 Year in Review.

What you need to know

Ontario’s energy resources generate energy differently, and each type of generation plays an important role in helping meet electricity demand.

  • Baseload generation: Nuclear power plants, which produce 60 per cent of Ontario’s energy, and run-of-the-river hydro facilities provide long-term, emissions-free generation that operates 24 hours a day, producing relatively the same output.
  • Peaking generation: Some generators are designed to increase and decrease energy output as needed − these include natural gas facilities and hydroelectric generators with dams. Generators like these, are relied upon to meet the "peaks" on the highest demand days.
  • Variable but controllable generation: Wind and solar facilities produce energy depending on how strong the wind blows and how bright the sun shines.When they are producing energy, these generators are highly flexible and can change output very quickly in response to system signals.
  • Distribution-connected generation:  Distribution-connected generators supply electricity to local distribution systems, which reduces demand on the transmission grid. Evolutions in technology and the electricity marketplace are expanding opportunities for participation in Ontario’s electricity system.

It’s not only energy resources that play a role in ensuring a reliable and cost-effective system. There are other tools that the IESO uses to ensure reliability.

  • The role of energy efficiency: Energy efficiency provides the cleanest and most cost-effective form of supply. It helps Ontario to cost-effectively meet its electricity system needs through the delivery of Save on Energy programs, training and education that enable Ontario’s electricity consumers to improve the energy efficiency of their homes, businesses, institutions and industrial facilities
  • The role of electricity imports and exports: Ontario's electricity grid is part of a greater network that spans North America. Ontario currently has interconnections with five of its neighbours: Quebec, Manitoba, Minnesota, Michigan and New York. By importing and exporting energy on a continual basis, the IESO has an important tool to help it balance the system. Electricity trades between these neighbouring jurisdictions provide operational and planning flexibility, as well as enhance the reliability and cost effectiveness of the Ontario electricity system.
  • The role of demand response: Through demand response, consumers reduce their electricity use in response to system needs and prices, providing a highly flexible resource. The IESO's Capacity Auction replaced the former Demand Response Auction to enable competition between additional resource types.

New supply will be needed to meet upcoming supply needs.

Ontario’s electricity needs are growing, with demand expected to increase one per cent each year for the next twenty years. Alongside these growing demand needs, the Pickering nuclear facility is retiring, a number of generator contracts are expiring, and nuclear facilities are undergoing refurbishment. The IESO’s first Annual Acquisition Report, outlines the framework to ensure the province has the supply needed to meet growing demand needs.

Ontario has a low-emission electricity system

In 2012, Ontario phased coal out of the electricity supply mix. In 2020, 94 per cent of Ontario’s energy output was from non-emitting resources.

Summer Peaking Electricity System 

Ontario’s electricity system has the highest peak demand during the summer months. The province used to peak in the winter, but with the increased adoption of air conditioners the demand peak season switched.

Decarbonization and Ontario’s Electricity System: Assessing the Impacts of Phasing Out Natural Gas Generation by 2030

Ontario homeowners, businesses, and organizations across many sectors, including municipalities, are actively pursuing new opportunities to accelerate decarbonization. By eliminating coal in our supply mix over a decade ago, today, our system is 93 per cent emissions-free and contributes only three per cent to the province’s total greenhouse gas emissions. 

Yet, with emissions from gas generation forecast to increase in the next few years, some Ontarians are asking whether the electricity sector can do more to support decarbonization goals by further reducing its carbon footprint. The IESO is listening and examined the question calling for the complete phase out of natural gas generation in the province by 2030. Our study shows that natural gas generation provides a level of flexibility to respond to changing system needs that would be impossible to replace in the span of just eight years. Read the full report.

Distributed Energy Resources make up ~5,000 MW of supply

There is a growing role of Distributed Energy Resources (DERs) in our supply mix, the IESO is working to provide more opportunities for businesses and communities to provide services to the grid through DERs.

Frequently Asked Questions

How can I learn more about the work happening around distributed energy resources (DERs) in Ontario? 

DERs offer an opportunity for communities to get involved in meeting their local electricity needs. Currently the IESO is engaging with stakeholders on DERs through the DERs roadmap engagement, which aims to establish IESO objectives, initiatives and timing for DER integration.

The IESO has published a study on the phase-out of gas in Ontario, what does the study state?

Ontario currently has one of the cleanest electricity systems in North America, and emissions account for just under three per cent of all emissions in the province. The IESO’s report assesses whether a phase-out of gas by a 2030 timeline is feasible. The assessment shows that retiring gas generation by 2030 would lead to blackouts and substantially higher electricity bills. While phasing out gas generation by 2030 would not be feasible, it could be considered given more time and planning.

Ontario’s electricity system is moving towards more-non emitting form of supply as well as supporting electrification in other sectors. The IESO is committed to looking at how the system can succeed on both fronts.

Why is there new electricity infrastructure being built in my region?

In certain pockets of the province, electricity demand is growing and requiring new solutions to help keep the lights on.  For example, economic development in southwest Ontario’s agriculture sector is leading to fast-increasing electricity demand. New transmission lines are bringing more power, while innovative local projects and consumer demand management are helping meet the region’s electricity needs.

How can I have a say in electricity infrastructure in my community?

By becoming part of your region’s local electricity network you can provide your voice on electricity activities and planning taking place in your community. Register to be a member of our Regional Electricity Networks on IESO Connects and participate in network discussions. 

Register here