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Ontario's Supply Mix

Ontario has a diverse power supply mix. Its generation fleet continues to evolve, using greener forms of supply to safely and reliably meet the province's changing electricity needs.

The IESO oversees Ontario's electricity system. It forecasts daily demand for electricity and operates in real time to ensure an adequate supply is always available. This includes managing the diverse characteristics of Ontario's generation fleet, making sure power generating units or other sources of supply are ready to ramp up and down production as needed.

Ontario's Energy Capacity and Output

There are currently 36,070  megawatts (MW) of installed transmission-connected generation in Ontario's electricity grid.  The amount of power available at any given time depends on the availability of fuel, whether a generator is on outage for maintenance and operating limitations of the facility.

Each generation type has a role in Ontario's supply mix. Nuclear and large hydroelectric sites operate at all times and provide a steady output known as baseload generation.  Other generation types such as gas and some hydroelectric stations ramp up production during peak periods of demand. Variable generation, such as wind and solar, produce energy depending on how much wind and sunlight is available. Yet, these sources are also flexible and can also change output quickly.   

Installed Energy Capacity by Fuel Type (December 2016)        


Generating resources as of December 15, 2016, updated quarterly based on the 18-Month Outlook. Note that these figures do not include generators that operate within local distribution service, except for those that participate in the IESO-administered market. Most solar facilities in Ontario are currently connected to the distribution system. 

Ontario's Long-Term Energy Plan outlines how the province's energy needs will be met over the coming years. It is based on the principles of cost effectiveness, reliability, clean energy, community engagement, and an emphasis on conservation and demand management before building new generation.

5 images of generation in Ontario

Ontario's Electricity Generation Fleet​​ ​

Ontario's electricity grid draws power from a combination of different energy sources. Learn about the role that each one plays in contributing to the province's total power supply mix.


Nuclear power plays a critical and foundational role in the province's supply mix, representing 13,000 MW or over 30 percent of Ontario's installed generation capacity and about 60 percent of the electricity produced in Ontario.

Ontario's nuclear fleet provides long-term, emissions-free, baseload electricity generation, that operates 24 hours a day at relatively the same output level. The cost of nuclear power is regulated for Ontario Power Generation (OPG) and is established through a contract for Bruce Power.

One of the advantages of having nuclear power in a supply mix is that the cost and output is independent of seasonal water availability, weather conditions or fluctuating gas prices.

Read more about the role of baseload generation.

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Hydroelectric generation is the most widely used form of renewable energy in Canada and around the world. Its significant contribution to Ontario's supply mix dates back to the early 20th century when it fuelled massive economic growth.  It remains a major contributor to Ontario's supply mix today, both as a form of baseload generation and during times of peak demand on the system. Ontario has around 8,400 MW of grid-connected hydroelectric capacity.  

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Waterpower Energy Explained

An interactive tool.


Hydroelectric generation harnesses the power of falling or downward flowing water. Along with nuclear generation, it contributes to the province's baseload power supply given its ability to produce large and reliable amounts of clean energy on demand.

Most hydroelectric generating stations use the natural run of the river, or a dam to raise the water level, to provide the drop needed to produce electricity. The water is diverted into a tunnel, which picks up speed and spins a turbine connected to a generator. The generator converts the energy into electricity.

Dozens of hydro generating stations can be found across Ontario on its many waterways. The highest producing stations are the Sir Adam Beck GS on the Niagara River, the Saunders Power Dam on the St. Lawrence River, and Des Joachims GS on the Ottawa River. Ontario's north is also home to numerous hydroelectric stations, such as the Aubrey Falls and Wells stations on the Mississagi River near Sault Ste. Marie.

In 2013, the Adam Beck II Station introduced into service, a massive four-storey tunnel that travels underneath downtown Niagara Falls. The tunnel diverts water from the Niagara River above the Horseshoe Falls and carries it on a downward slope to the generating station over 10 kilometres down river, substantially increasing the station's generating capacity. The tunnel will deliver a low-maintenance, clean source of energy for the next century.

Natural Gas

The role of natural gas generation in Ontario's supply mix has increased in recent years with the phase out of coal-fired generation. Natural gas has approximately 10,000 MW of installed capacity. It is often used to ensure a reliable power supply during higher demand times.​

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Ontario has made significant efforts over the last decade to become a wind energy leader in Canada. Ontario currently has over 3,800 MW of installed wind capacity.

The IESO publishes an interactive Ontario Wind Map that visually displays the province's hourly wind forecast, as well as the last hour's total output from all transmission-connected wind facilities.

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Currently, most solar generation in the province is embedded on local distribution systems. Production ranges from small-scale generation by farmers, homeowners, and businesses to larger operations like the 97 MW Sarnia Photovoltaic Power Plant.

Solar Energy Explained

An interactive tool.

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Demand Response

The demand side of the system is taking on a more prominent role in the system. Read more about how consumers are contributing to system needs.

With coal generation phased out in Southern Ontario, Atikokan Generating Station has been converted from coal to biofuel generation. Thunder Bay has also been converted to biofuel. 

Biofuel is a renewable energy resource produced from the environmentally friendly breakdown of organic materials.  The province already has roughly 495 MW in other biofuel or waste wood burning generation facilities.