Home > Ontario's Power System

Ontario's Power System

​​​​​​Ontarians use more than 140 million megawatt hours of electricity a year. Ensuring that there is enough energy to meet that demand is an ongoing and highly-complex process, requiring the close co-ordination of all parts of the system. The IESO is at the centre of it all, directing the flow of power across the province. This section provides an overview of Ontario's power system— from the first flick of a light switch to the final statement on the electricity bill —  ​and everything in between.

Ensuring A Reliable System

Photo of IESO Control Room and Operators

The IESO ensures that Ontario's power system operates reliably so that power is available when and where it is needed. Ontario's supply outlook remains positive, yet maintaining flexibility for both supply and demand is key to ensuring efficiency as the power system continues to evolve.


Demand forecasts help the IESO assess whether there will be adequate generation and transmission facilities to meet those needs. These assessments are regularly published in the ​quarterly 18-Month Outlook.

The IESO works to ensure the reliability of the power grid at all times by being ready for emergency situations and potential system events.  It oversees emergency preparedness for the province's electricity system through extensive planning and coordination with market participants and regional counterparts.