Southwest Ontario Bulk Planning
Electricity Demand
Bulk electricity planning ensures Ontario’s transmission system can deliver reliable, affordable, and sustainable electricity where and when it is needed. As demand grows across the province, bulk planning helps ensure the system has the infrastructure required to support economic development and electrification across the province.
Electricity demand in southwest Ontario is growing rapidly, driven by economic development in the agriculture and manufacturing sectors, as well as electrification initiatives.
In response to growing needs and various scenarios, the IESO has made recommendations to enhance the bulk transmission system in southwest Ontario. The following provides a general overview of recent bulk planning activities in the region.
Engagement
The IESO engages with communities, stakeholders, and the public to build awareness of our work and seek input that helps to inform our decision-making.
Learn more about how the IESO approaches our engagement activities
Related Information
- Discover how the IESO powers progress across Ontario by exploring our Digital Guides.
- Explore current engagement opportunities
- View planning initiatives
- Read the Integrated Bulk Power System Planning Process - High-Level Design Overview for details on the high-level design of the bulk system planning process
- Subscribe to receive updates on a variety of the IESO’s activities
Active Bulk Plans
The Niagara Region and surrounding areas are experiencing strong and ongoing economic activity. As electricity demand continues to grow across the area, there is a need to assess whether the high-voltage bulk transmission system can maintain reliability across the Queenston Flow West (QFW) interface. Four locations where significant load growth is expected, or where changes in electricity demand could have a meaningful impact on the QFW, will be assessed under a range of load levels, including the Welland, Thorold and Hamilton areas. This bulk plan primarily encompasses Niagara Region, including the lower-tier municipalities, City of Hamilton, City of Burlington, Haldimand County and County of Brant.
Supporting Materials and Resources
Completed Bulk Plans
The South and Central Bulk Plan was initiated in 2024 to assess transmission reinforcements required to enable the connection of small modular reactors near Darlington Nuclear Generating Station and expanded nuclear at the Bruce Power site; emerging demand across the Greater Toronto Area (GTA) and the Windsor–Hamilton corridor; the flow of electricity across multiple pathways; and the ability to connect to new large sources of demand that support economic development.
To manage costs and maintain flexibility, the IESO recommends a staged approach to transmission planning that can adapt as electricity demand, procurement outcomes, and policy direction evolve.
Early actions were advanced during the initial stages of the South and Central Bulk Plan because there was strong confidence they would be needed. These included:
- A new transmission line from Bowmanville to the eastern GTA to connect small modular reactors and other electricity supply resources.
- Reconductoring a transmission line between Barrie and Orangeville.
- Corridor preservation studies for potential future transmission infrastructure.
Implementation-ready actions are investments that should begin now to meet the region's electricity needs by the early 2030s. Based on input from communities and stakeholders, the IESO recommends five new or upgraded stations in Milton, Barrie, Vaughan, Puslinch, and Guelph to support population growth, electrification, and economic development.
The IESO also recommends new transmission lines between Vaughan and Toronto, Strathroy-Caradoc and Guelph, and Guelph and Puslinch to increase system capacity, improve reliability, and enable new electricity supply. Given the long development timelines for transmission projects, these investments should move forward immediately, with in-service dates between 2030 and 2034.
Future-consideration actions help preserve the region's ability to respond to longer-term growth and changing electricity system needs. These investments are not required immediately but may be needed to support future demand growth, new electricity supply, or evolving policy priorities. By advancing them only when needed, the IESO can maintain flexibility while managing costs for ratepayers.
For the South and Central Bulk Plan, these actions include a new transformer station in the London area, transmission infrastructure to enable the proposed Bruce C nuclear project, and a new transmission line between London and Lakeshore to support future growth in southwestern Ontario.
The IESO will continue to monitor system needs and advance these investments as conditions evolve.
More details can be found in the Final Report.
Supporting Materials and Resources
Report: South and Central Bulk Plan
The Northern Ontario Bulk Plan: North-South Transmission Reinforcement Plan was developed to support growing electricity demand in northern Ontario, and to increase the transfer capability to areas south of Sudbury to Barrie, enabling the siting of additional generation in the region. For more information, please visit the engagement page.
Supporting Materials and Resources
Report: Northern Ontario Bulk Study: North-South Transmission Reinforcement Plan
Hydro One: Sudbury Barrie Transmission Line (Hanmer TS to Essa TS)
The Central-West Bulk Plan assessed the bulk transmission system between Hamilton and London, considering the potential economic development opportunities emerging in the region. The plan’s scope was expanded to assess the bulk transmission system from Hamilton to Windsor and considered other potential demand growth across southwestern Ontario.
To meet the region’s needs, the plan recommended rebuilding a section of the existing M31W circuit from Buchanan TS (near London) to the Firm Load tap located approximately 2 to 5 km to the east of the station. Should load continue to grow, dynamic voltage devices can be implemented.
Supporting Materials and Resources
Report: Central-West Bulk Plan
The West of London Bulk Plan assessed the bulk transmission system in the Windsor-Essex and Chatham-Kent areas to ensure there is adequate supply to the area, identify any transmission constraints, and meet the rapid agricultural load growth. To meet the needs, this plan recommended:
- A new 230 kV transmission line from Lambton TS (Lambton County) to Chatham SS (Chatham-Kent) to be in-service no later than 2028;
- The continued operation of the Brighton Beach Generating Station to support local needs in the near term until the Lambton to Chatham transmission line is in-service;
- A new 500 kV transmission line from Longwood TS (Strathroy-Caradoc) to Lakeshore TS (Lakeshore) to be in-service in 2030; and
- 550 MW of local resources needed by 2035 that can be met by reacquiring resources whose contracts have expired or by acquiring new resources.
Supporting Materials and Resources
Report: West of London Bulk Planning Report
Data Tables: West of London Bulk
Letter: IESO Hand-Off Letter to Hydro One Regarding the Transmission Line from Lambton to Chatham
Hydro One: Longwood to Lakeshore Project (Longwood TS to Lakeshore TS)
Hydro One: St. Clair Transmission Line (Lambton TS to Chatham SS)
The Windsor-Essex bulk plan was triggered by the forecasted electricity demand growth in the Kingsville-Leamington area, which was expected to double between 2019-2024. It recommended two transmission reinforcements, a switching station at the Leamington Junction (Lakeshore), and a new transmission line from Chatham SS (Chatham-Kent) to Lakeshore SS (Lakeshore).
A companion 2015 Integrated Regional Resource Plan (IRRP) was also completed. It focused on providing customers in the region with adequate line connection, step-down transformation capacity, and maintaining a level of reliability consistent with planning standards. Information from the IRRP, such as demand forecasts and plans for new connection facilities, informed this bulk plan.
Supporting Materials and Resources
Report: Need for Bulk Transmission Reinforcement in the Windsor-Essex Region
Letter: IESO Hand-Off Letter to Hydro One Regarding the Leamington Switching Station
Letter: IESO Hand-Off Letter to Hydro One Regarding the Transmission Line from Chatham to Lakeshore
Hydro One: Lakeshore Transformer Station Project
Hydro One: Chatham to Lakeshore Line (Chatham SS to Lakeshore SS)