Ontario approves $1.5-billion underwater electricity cable from Darlington to Toronto

Ontario approved construction of the Third Line, a roughly 65-kilometre underwater transmission cable from Darlington Nuclear Generating Station to Toronto, estimated at about $1.5 billion and designed to carry roughly 900 megawatts.

Ontario's government has approved construction of a new underwater transmission line that will link the Darlington Nuclear Generating Station to a terminal in Toronto's Portlands district. Known as the Third Line, the project is planned to run about 65 kilometres along the bottom of Lake Ontario. Officials described the cable as having about 900 megawatts of transmission capacity and said it is intended to support expected growth in Toronto's electricity needs. The province gave a high-level cost estimate of roughly $1.5 billion and said procurement and construction steps will follow. Key details: - The line would span about 65 kilometres under Lake Ontario from Darlington in Clarington to a terminal in the Portlands east of downtown Toronto. - Officials said the cable would have a transmission capacity of about 900 megawatts, roughly matching the output of three planned 300-megawatt small modular reactors at Darlington. - The government cited a high-level cost estimate near $1.5 billion, and officials noted an overall range of $750 million to $3 billion. - A competitive procurement process is planned later this year; officials said construction would begin next year and continue for seven to ten years, with the line to be in service by 2037 at the latest. - The Independent Electricity System Operator (IESO) told officials the underwater option would provide greater long-term capacity than two land-based alternatives and would meet demand scenarios "well into the 2050s." The IESO said land options would meet needs only until about 2040. - Officials said the subsea cable would be more resilient to storms and extreme weather than overland lines. The IESO has also reported that Toronto's peak electricity demand could nearly double within 20 years and that winter peaks may arrive as soon as the early 2030s. Summary: The approval advances the Third Line into procurement and early construction planning, with officials aiming to select a builder later this year and begin construction next year. If completed by the target date, the 900-megawatt underwater cable is intended to add long-term transmission capacity for Toronto and reduce local reliance on the Portlands natural-gas plant, though the IESO noted the gas station may still be needed for some peak conditions. Undetermined at this time.