Ontario's supply and demand of electricity must be kept in balance every minute of the day. The IESO forecasts hourly demand to ensure that sufficient generation will be available to meet that peak. The level of demand is primarily influenced by factors like weather, hours of daylight, business hours, school holidays, and daily consumption patterns. At certain times of the year demand in the middle of the night can go lower than 11,000 megawatts (MW) and then rise by more than 10,000 MW later the same day.
Here are some historical demand numbers that illustrate the variety of demand conditions experienced in Ontario.
Forecasting Demand - Peak and Energy
The IESO forecasts demand for electricity in the province for the next 18-months and assesses whether the existing and proposed generation and transmission facilities are adequate to meet those needs. Normal Weather forecasts represent a typical peak for that time of year, while Extreme Weather peaks reflect severe weather conditions, such as humidex of 50°C.
Numbers shown here are as of December 2016. Read the
18-Month Outlook to find out more about the demand forecast.
Total Annual Ontario Energy Demand
Megawatt (MW) is a unit of electrical power equal to one million watts. (A typical light bulb uses 100 W of power). A
Megawatt-hour (MWh) is the measure of one million watts produced or consumed in one hour. For example, one MWh is enough electricity to power 10,000 light bulbs for an hour. A
Gigawatt-hour (GWh) is equal to 1,000 MWh. A
Terawatt-hour (TWh) is equal to 1,000 GWh.
Electricity Demand Records
The all-time record for Ontario demand was set on Tuesday, August 01, 2006, when peak demand for electricity reached
Here are the top twenty record demand days for the Province of Ontario:
Ontario Demand (MW)
1||Tuesday, August 01, 2006||27,005|
2||Wednesday, July 13, 2005||26,160|
3||Monday, June 27, 2005||26,157|
4||Monday, July 31, 2006||26,092|
5||Monday, July 17, 2006||25,898|
6||Tuesday, June 28, 2005||25,861|
7||Monday, July 18, 2005||25,857|
8||Wednesday, August 02, 2006||25,816|
9||Tuesday, August 09, 2005||25,816|
10||Tuesday, July 12, 2005||25,808|
11||Tuesday, June 26, 2007||25,737|
12||Thursday, August 02, 2007||25,584|
13||Monday, July 11, 2005||25,506|
14||Wednesday, June 27, 2007||25,467|
15||Thursday, July 21, 2011||25,450|
16||Tuesday, August 13, 2002||25,414|
17||Wednesday, August 01, 2007||25,402|
18||Thursday, July 21, 2005||25,383|
19||Thursday, July 14, 2005||25,362|
20||Monday, August 12, 2002||25,349|
More Demand Records
The record minimum electricity demand set on April 4, 2010 was 10,618 MW.
The winter peak for electricity demand set on December 20, 2004 was 24,979 MW.
The summer peak for electricity demand set on August 1, 2006 was 27, 005 MW.
Peak Demand Across the Province
For some communities, peak demand occurs in the winter, while others are in the summer. Peak demands for select communities across the province are shown below.
Typically a summer-peaking province, Ontario experienced the first annual winter peak in a decade in 2014.
Local data taken from the Ontario Energy Board's
Download Data (.csv)
For a complete listing of reports, see