Energy Resources: How They Work

Ontario's electricity grid draws power from a variety of different energy resources. Learn how they work.

Collage of generation resources

Wind power

Wind generating stations use moving air to create electricity. As the wind passes through the turbines, it moves the blades that spin a shaft that is connected to a generator. The amount of energy generated is determined by the speed of the wind. Wind speed is usually strongest during cold winter months and at night, but can vary depending on geography and the time of year. Wind is a suitable complement to solar generation which produces higher production values during hot spring and summer days.

Wind generators can change output very quickly. The IESO is able to instruct transmission-connected wind facilities to increase or decrease output in response to system conditions, such as when there is more generation from baseload resources than needed, or to reduce congestion along transmission lines in certain areas. See hourly forecasts and real-time output of Ontario wind facilities on IESO’s Wind Power in Ontario map.

Did you know?

Ontario is the wind energy leader in Canada with more than 4,300 MW of installed capacity through both transmission-connected and distribution-connected (embedded) wind generators.

Solar photovoltaic

Solar generation is a renewable energy source fuelled by the sun. Large panels made of 'solar cells' collect sunlight and convert it directly into electricity. Similar to wind power, solar generation is a variable resource as it is reliant on the weather, time of year and time of day. Its contribution is particularly important in the summer months when peak demands occur midday as solar panels reach their height of production. Output ranges from small-scale generation by homeowners, farmers, community groups and others to larger-scale operations connected to the transmission grid. Currently most solar generation is embedded within local distribution systems. 

Did you know?

Most of Ontario’s solar power is produced by small scale generators within the local distribution system.


Hydro, also referred to as hydroelectric or waterpower, is a renewable source of energy produced by the falling or moving of water. Most hydroelectric generating stations use the natural drop of the river, such as a waterfall or rapids, or a dam to create the driving force of water to turn the blades of the turbine that is connected to a generator. The water, having served its purpose, exits the generating station where it rejoins the main stream of the river. Hydro is a major contributor to Ontario’s supply mix, both as a form of baseload generation and during times of peak demand. Hundreds of hydro generating stations can be found across Ontario on its many waterways.

Did you know?

Hydroelectric generation is the most widely-used form of renewable energy in Canada and around the world.  


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. Ontario’s three nuclear facilities typically produce about 60 percent of the province’s electricity. In nuclear power production, the splitting of uranium atoms, in a process called fission, creates heat to make steam that drive turbines to make electricity. Ontario's nuclear fleet provides long-term, emissions-free, baseload electricity generation, that operates 24 hours a day at relatively the same output level.

Learn about the role of baseload generation in helping to support a reliable power system.

Did you know?

  • Nuclear power has been a staple of Ontario's supply mix for more than four decades.
  • Each site uses Canadian-developed CANDU nuclear reactors.
  • Bruce Nuclear Generating Station is the world’s largest operating nuclear facility.

Learn more about Ontario’s nuclear power generating stations.

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 makes up approximately 10,000 MW of the province’s installed capacity. It is often used to ensure a reliable power supply during times of higher demand and can provide needed flexibility in response to conditions on the power system. Natural gas can be used to generate electricity in a variety of ways. Many of the new natural gas fired power plants are known as ‘combined-cycle’ units which feature gas and steam turbines. The gas turbine generates electricity using natural gas fuel, while the steam turbine generates electricity using waste heat from the gas turbine. The process is extremely efficient since exhaust heat is re-used that would otherwise be lost through the exhaust stack.

Did you know?

Natural gas is the cleanest of the conventional fossil fuel types.


Bioenergy refers to the conversion of energy from organic matter (biofuel) to produce electricity. Ontario has plentiful sources of biofuels including residual materials from forestry operations that are left to decay on the forest floor, waste matter from agricultural production and animal livestock activities, by-products of food-processing operations, and municipal waste from landfills, compost, and water treatment facilities.

Biomass materials such as plants and animal waste are burned in their original form or in pellets to generate electricity. Biogas is made by fermenting organic materials such as manure and other agricultural waste to produce methane gas which is then combusted to create electrical energy. The production-and-use cycle is continuous and is considered to be carbon neutral.

Ontario has almost 500 MW in bioenergy capacity. Approximately one-quarter of Ontario’s bioenergy capacity is produced at the distribution system level in small scale projects.

Did you know?

Two of Ontario's former coal generation stations, Thunder Bay and Atikokan, have been converted from coal to bioenergy.

Energy storage

Emerging energy storage technologies are allowing electricity to be captured and stored and then re-injected back into the grid when it is required. Energy storage technologies vary considerably in terms of: their size and scale, how the energy is stored, how long it can be stored and the technology’s response time. The IESO has contracted for a variety of energy storage technologies in order to understand how storage can be integrated into the power system and used to support day-to-day operations of the system and market. Learn more about these energy storage projects

Read more about energy storage technologies

The examples below illustrate various energy storage concepts and may not necessarily meet the definition of energy storage used in IESO procurements and various regulatory instruments.

Energy storage batteries

Battery energy storage systems are able to convert chemical energy into electrical energy. The electrolytes allow ions to move between the electrodes, allowing currents to flow from the battery to provide energy. During charging, the reverse reactions happen and the battery is recharged by applying an external voltage to the electrodes.

Capable of changing their output in less than one second, some types of batteries are now being used by grid operators to quickly balance variations in load to regulate frequency. Battery systems are also often found at the distribution system level and at individual customer sites. Other forms of battery technology are at various stages of technological development and show promising future potential.


A flywheel stores kinetic energy in a rotating mass. When electricity demand is low, the flywheel uses power to drive a motor that spins the flywheel at high speeds, allowing excess energy to be stored. When energy is needed, the spinning force drives a device similar to a turbine to produce electricity, slowing the rate of rotation. A flywheel is recharged by using the motor to increase its rotational speed once again. Like batteries, flywheels can both store and quickly release energy as needed.

Compressed air energy storage

Compressed air uses off-peak energy to pump air into a containment area such an underground cavern or over ground tanks, where it is held until needed. It is then released through an expansion turbine. In some cases, this may be done in conjunction with natural gas fuel, which increases the efficiency of the generator to provide more efficient energy during peak hours. Conversely, vacuum air storage systems are the mirror image of compressed air arrangements, where off-peak energy is used to create a vacuum, which is later re-pressurized, creating an airflow used for power generation when needed. 

Electric vehicles

Electric vehicles−and their batteries−can be considered as both controllable load during periods of lower demand and a source of supply during times of higher demand with the appropriate technologies. Using smart electric vehicle charging stations, customers would supply the grid or use the electricity to meet their own energy needs.

Thermal energy storage

Not all stored energy necessarily comes directly back to the power grid as electricity. Off-peak energy can be stored as thermal energy, which can then be used to supply heating and/or hot water needs, reducing electricity consumption during on-peak periods.  Increasingly, solar thermal systems are being used around the world to supplement or replace the electrical energy drawn from the grid for such uses.  Ice storage systems do just the opposite where off-peak energy is used to make large blocks of ice to help cool buildings during peak hours. Other more sophisticated, high-temperature thermal storage systems can also be used to generate steam for electricity production to supply back to the grid.

Fuel production

Electricity can be used as an input in the production of other types of fuels such as hydrogen and biofuels. These fuels act as an energy storage medium and can be used to generate electricity. Off-peak electricity can also be used for compressing natural gas−an emerging usage in the transportation sector.   

Magnetic energy storage

Magnetic fields are capable of storing electrical energy, and when coupled with superconductors, the storage potential can be significant. Some pilot projects involving superconducting magnetic energy storage are currently under development at various laboratories and utility equipment providers around the world. However, the future success of these new forms of energy storage devices is highly dependent on the cost of the superconductors themselves. Magnetic energy storage is suitable for short-term storage.

Pumped Storage

Pumped storage is essentially hydroelectric power that takes advantage of lower-priced periods to pump water into a reservoir, and then releases the water when needed. Presently, it is the most established and widely used form of energy storage in the world. Ontario has one large-scale pump generation project: Ontario Power Generation's pump-generation facility in Niagara, which has been operating since 1957. This 174 megawatt facility has helped meet peak supply, manage surplus conditions, provide regulation services, and operating reserve.