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Backgrounder - Factors Affecting Demand

Demand patterns in Ontario are impacted by factors like weather, holidays and major events. As part of its responsibility to maintain reliability, the IESO incorporates these influences into its demand forecasts.


Temperature, wind, and precipitation all have a significant impact on electricity demand, sunflowers.gifas consumers react and adjsut their lighting, heating or cooling needs in response:

  • On extremely hot days, electricity demand increases due to air conditioning usage.
  • During heatwaves, energy use tends to increase over subsequent days, even if the temperature does not.  As heat builds up in homes and buildings, air conditioners need to work harder to maintain cooler temperatures.
  • Each degree above 16�C raises demand by 150 MW to as much as 450 MW per degree at 35�C, as air conditioners draw increasing amounts of energy from the grid.
  • Each degree below 10�C raises demand by 50 MW to as much as 250 MW a degree at -20�C, mostly due
    to iSnowstorm.jpgncreased electricity use from furnaces.
  • Cloud cover in the summer can reduce demand by as much as 1,000 MW by creating a shade protection from the sun. If it's too cloudy, however, that will increase lighting load.
  • In winter, cloud cover and snowfall contributes to increased lighting load by as much as 750 MW.
  • Wind can cool equipment, having the same impact as reducing the temperature by five degrees. Strong winds (30 km/h and up) on very cold days can increase demand by 800 MW.
  • Thunderstorms on hot summer days can reduce temperatures by as much as 10 �C, bringing demand down by over 1,000 MW.

Statutory Holidays

Canada flagPublic holidays bring lower demands as many businesses close and Ontarians take time off to relax. Typical demand reductions seen on statutory holidays include:

  • Victoria Day:  -2,400 MW
  • Canada Day:  -1,700 MW
  • Thanksgiving: -2,500 MW
  • Christmas Day: -4,400 MW

Major Events

Major television and public events that change Ontarians' consumption behaviour can have a direct impact on demand patterns. Recent examples include:

  • So many Ontarians watched the Men's hockey finals at the Vancouver Olympics that the opening faceoff and the moment of Sidney Crosby's winning goal can be seen just by tracking Ontario's surges in demand.  Energy use rose during intermissions and dipped again when play resumed.

Ontario Electricity Demand - February 28, 2010 


  • Ontario demand typically drops 300 to 350 MW at 11:00 a.m. every Remembrance Day as Ontarians pause for a moment of silence.
  • When clocks revert back to Eastern Standard Time (EST) in fall � the peaks in the evening can become quite steep. With night falling earlier in the evening, the need for more home lighting and energy to prepare dinner plus the "Nintendo" load (when kids come home from school) all combine to increase the evening peak by 750 MW.