GTA East

Map of Ontario showing 21 electricity planning regions

Area Overview

The GTA East region extends from Lake Ontario northward to the southern parts of Scugog and Uxbridge, and includes the municipalities of Pickering, Ajax, Whitby, Oshawa and parts of Clarington within Durham Region. The area is supplied by several transformer stations fed by the 230 kV transmission system in the area. Electrical usage in this region is comprised of a mix of residential, commercial, and industrial customers. Strong residential growth is being seen in many areas across the GTA East region. This is primarily driven by urban intensification throughout Pickering Ajax, Whitby, and Oshawa, as well as new community growth in northern Pickering. Industrial customer demand has also increased in recent years, through a combination of new facilities, and conversion of existing end uses to electricity supply.

The local distribution companies providing service to customers in the area include:

  • Elexicon Energy
  • Hydro One Networks Inc.
  • Oshawa PUC Networks

Community Engagement

The IESO engages with local and regional communities to seek input to help inform planning activities. There are currently no active regional planning engagement activities for this region. See Key Resources below for the latest planning documents.

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Regional Planning Progress Update

A Needs Assessment, the first step in the planning process, was completed for the second cycle of Regional Planning in August 2019, and did not identify any needs in the area requiring regional coordination and integrated planning at that time. The Needs Assessment report is available on Hydro One's regional planning page for the GTA East region.

The first regional planning cycle was completed with the release of an Integrated Regional Resource Plan (IRRP) in June 2016 and Regional Infrastructure Plan in January 2017, specifically for the Pickering-Ajax-Whitby sub-region. Similarly, the Needs Assessment completed at that time did not identify any needs requiring regional coordination for the Oshawa-Clarington sub-region.

Key Resources

Related Studies

Connection Approach for SMRs at Darlington NGS

OPG’s first Small Modular Reactor (SMR) is currently under development, and is scheduled to be in commercial operation by 2029 but connected to the grid by 2027, with three additional SMRs scheduled to be in service by 2035. All four SMRs will be located on the Darlington nuclear generator station (NGS) site, and combined represent 1200 MW of new system capacity. Based on previous assessments, Hydro One and OPG had begun initial development work to connect the first SMR to the 230 kV system, at Clarington TS, rather than the 500 kV network. However, recent studies, including the IESO’s Pathways to Decarbonization study completed in late 2022 and the subsequent direction from the Province’s Powering Ontario’s Growth report in July, 2023, identified a number of system changes that will impact anticipated flows on the 500 kV network between Bowmanville and Pickering. As a result, the connection arrangement has been revisited in this report.

Based on the revised outlook for the future system, the IESO recommends a phased connection through the 500 kV system, including the development of a new expanded switching station at Bowmanville SS, and the initiation of a bulk system study to identify the scope of future transmission expansion to the 500 kV system that may be required in the Eastern GTA. View the report.

Gatineau Transmission Corridor

A Bulk Planning Initiative has recently been completed in Eastern Ontario for the Gatineau Transmission Corridor. The study, published in December 2022, examined options to address transmission equipment reaching end-of-life (EOL) in this corridor along with forecasted reliability concerns in the areas of Ottawa and Peterborough to Quinte West (which are supplied by the circuits located within this corridor). Among the outcomes of this study is a recommendation to build a new double-circuit 230 kV transmission line into Dobbin TS (in Peterborough) from either Cherrywood TS (in Pickering) or Clarington TS (in Oshawa) with a planned in-service date of 2029.

As indicated in the study report, the option to terminate at Cherrywood TS may have the added benefit of improving the load meeting capability in the GTA East region, namely within northern Pickering and Whitby. This would be achieved by providing additional circuit capacity in the vicinity of anticipated growth, potentially allowing for the connection of an additional step down station without the need for additional system upgrades. Elexicon Energy (the LDC for Pickering and Whitby) has indicated to the IESO through regular conversations between planning cycles that higher than anticipated growth is being observed within these areas, which may trigger the need for new capacity within the medium term. Consistent with the Gatineau study findings, the IESO has acknowledged that the Cherrywood connection option for the new line could be an option to address capacity needs in the area, and encourages this additional benefit to be considered along with other factors in the development of a preferred route for the transmission line.

This information will be carried forward into the next cycle of regional planning, scheduled to be initiated in Q3/4 2024.

Additional information on the Gatineau Corridor End-Of-Life Study.