Ontario needs substantially more electricity, but the first gap it will face is not a massive shortage of peak generation capacity; it is a shortage of annual clean energy. Electricity demand reached 145.6 terawatt-hours in 2025, an increase of 4.4% in one year, while the reference case scenario of the Independent Electricity System Operator of Ontario (IESO) reaches 250 terawatt-hours by 2050. However, the forecast range extends from 207 to 297 terawatt-hours, a disparity that significantly changes the scale of infrastructure required.
According to the analysis, after accounting for projects already under construction, the province will face a shortfall of more than 8 terawatt-hours of annual energy in 2032, and more than 12 terawatt-hours in 2035. The additional summer capacity gap does not appear until 2035, and initially amounts to only about 950 megawatts. The author therefore argues that the priority should be adding clean electricity year-round, rather than immediately seeking massive quantities of new peak capacity.
Energy and flexibility are different products
The analysis emphasizes that the word “capacity” does not describe the same function for every grid resource. A wind plant generates electricity when the wind blows, while a battery adds almost no net annual energy but shifts electricity to the hours when it is most useful. Hydroelectric power can provide both energy and flexibility, while transmission allows electricity generated in other areas to be used. Demand response can also reduce peak consumption without generating additional electricity, while nuclear generation provides large quantities of low-carbon electricity and dependable capacity for decades.
Accordingly, treating these resources as though they sell the same product could lead to an unsuitable investment mix. The author proposes that Ontario begin with the resources that can be added most quickly and are best able to address the near-term gap, then determine the scale of new nuclear expansion based on the remaining needs that persist afterward.
Wind and solar procurements return
Ontario has resumed procuring wind and solar power after more than a decade without a major procurement of new renewable-energy projects. The first energy window under the LT2 program resulted in contracts for projects with a combined capacity of 1,115 megawatts, expected to produce approximately 2.37 terawatt-hours annually.
IESO said the initially selected project prices were 21% lower than those in the previous comparable large renewable-energy procurement. This does not mean that wind and solar alone can solve all of the grid’s problems, but it shows, according to the analysis, that Ontario can add a meaningful amount of clean electricity within a few years without deciding the full shape of its generation fleet through 2045.
Storage and reducing reliance on gas
The province has also expanded its procurement of resources that help it use more wind and solar without excessive reliance on gas. The latest capacity window under LT2 added approximately 640 megawatts of batteries, raising contracted storage to more than 3.5 gigawatts by 2030. Prices in this round were 36% lower than in the first expedited procurement for long-duration batteries, and 16% lower than in the first regular procurement.
The author considers the decline in prices with repeated procurements to give planners real information about current storage costs, rather than requiring them to estimate its costs two decades from now. But adding clean energy alone is not enough, because gas performs around-the-clock operational functions, including providing reserves, following changes in load, and responding to frequency.
Gas- and oil-fired generation connected to the transmission grid rose from 9.7 terawatt-hours in 2020 to 31.4 terawatt-hours in 2025, at a time when nuclear generation declined because of refurbishment work and outages. Gas’s share of generation connected to the transmission grid also rose from 7% to 19.3% over five years. The analysis argues that reducing this share requires replacing the functions gas performs hour by hour, not merely adding another large source of annual low-carbon energy. Batteries, hydroelectric power, transmission lines and interconnections with other grids, and controllable demand can perform increasing portions of these functions.
Nuclear refurbishment does not mean ordering new reactors immediately
The analysis does not call for shutting down existing reactors. Ontario’s nuclear fleet is one of its most important low-carbon assets, and the record of recent refurbishment work is positive. The refurbishment of Darlington Station was completed ahead of the overall schedule and under budget, while Unit 3 at Bruce Station returned to service seven months ahead of schedule and under budget.
The author distinguishes between extending the operating life of existing reactors at sites that already have transmission lines, trained workers, and operating institutions, and deciding to build a large number of new reactors in the 2040s. According to the analysis, the small modular reactors at Darlington represent a riskier path than the refurbishment program because they rely on GE Hitachi’s BWRX-300 boiling-water reactor, a design Ontario has never operated before, with a fuel cycle and supply chain different from those of the CANDU fleet.
The province also has not built a new reactor in decades, so it cannot simply be assumed that the institutional capabilities that built the original fleet remain ready. The first four units may provide useful evidence, but they should be treated as a high-risk initial nuclear program in terms of design, cost, and schedule, not as proof that small reactors have already solved the problems of building nuclear plants.
Long-term decisions need better information
Wesleyville may eventually accommodate up to 10 gigawatts of generation, while the Bruce C project is advancing through the pre-development stage. The author considers it sensible to keep these options available, particularly given that IESO’s demand scenarios differ by approximately 90 terawatt-hours in 2050. Committing now to building all of this capacity is not equally justified.
If demand approaches the high scenario and a large clean-generation gap remains after adding renewables, storage, and flexible demand, major nuclear expansion may become appropriate. But if demand approaches the reference or low scenario, and the costs of renewables, storage, and flexible demand continue to decline, Ontario may not need new nuclear construction economically.
The author’s recommendation, in summary, is to deploy the fastest resources first, continue refurbishing reactors that demonstrate their value, learn from the small reactors under construction, and keep the larger nuclear sites available. Once better information is available, costly and long-lived decisions about new nuclear generation can be made. The author also criticizes turning renewable energy into a political issue for years, while warning against replacing one predetermined political answer with another; the standard, in the author’s view, is the mix that provides enough clean electricity, replaces gas’s flexibility, and leaves the smallest costly gap for new firm generation.