How reliable is Ontario’s electricity supply?

This month marked the 15th anniversary of the infamous 2003 Northeast Blackout. Though not caused by issues in Ontario, the blackout showed how crucial a reliable supply of electricity is to our economy and current way of life. Concerns about not having enough power to maintain reliability played a significant role in the province’s decision to invest in: 1) new generation; and 2) electricity conservation programs in the mid 2000s.

This image shows states and provinces that experienced power outages from the 2003 Northeast blackout. Not all areas within these political boundaries were affected. Source: Wikipedia.

Ontario’s experience of the Northeast Blackout of 2003

On August 14, 2003, a technical glitch at an Ohio-based generating station resulted in a domino effect that led to this massive power outage. More than 100 power plants shut down along the northeast, including in Ontario, leaving close to 50 million North Americans in the dark for up to 2 days. Ontario lost 18.9 million work hours, and the whole affected area (over 24,000 square kilometres) lost an estimated $6.5 billion in economic earnings.

Our power struggle in the early 2000s

The province’s ability to adequately and reliably provide electricity at all hours to Ontarians, especially during peak hours, was of concern before the blackout. Supply struggled to keep up with growth in demand. Between 1996 and 2003, Ontario’s generation capacity fell by 6% while demand grew by 8.5%.

Investments in new generation were modest during these years; less than half of what is spent today was being used to maintain and upgrade transmission and distribution assets. By the early 2000s, rolling brownouts and public appeals by Ontario’s Independent Electricity System Operator (IESO) to conserve electricity during peak hours were common on hot summer days (see example of appeal issued in June 2005 during a period of high demand in Ontario).

Investments to improve reliability and meet requirements

After the 2008/2009 recession, Ontario improved its reliability to meet peak demand for electricity by growing supply as the annual peak demand remained flat (shown in the graph below). However, as the gap between generation capacity and actual peak demand has grown, people have raised concerns that Ontario overinvested in supply and conservation, increasing electricity bills.

Actual peak demand vs. installed capacity for Ontario, 2009-2017 Source: “Media: Year End Data”, online: Independent Electricity System Operator [Accessed 6 March 2018].


Ontario currently does have enough electricity to meet demand at all hours due to its investments in conservation and electricity generation, as explained in Q5 of our 2018 Energy Conservation Progress Report, Making Connections, However, the amount of electricity supply available to meet Ontario’s peak demand is adequate, but not excessive, for the following reasons:

1. The province must have sufficient capacity to meet high demand at all times.

Our electricity grid must have an adequate electricity supply during all hours of the day, especially when demand is the highest – even if peak demand is for only a few hours. The difference between the highest and lowest demand in a year can be as much as 13,000 MW, as shown in the figure below.

Hourly electricity demand patterns over a week in January, April and July-August of 2017. Note: Actual hourly demand is slightly higher than shown here, particularly during the daytime in summer hours, because some demand is served by embedded generation (primarily solar) connected to local distribution systems. See Q5 to read more about the impact of solar generation in reducing peak demand. Source: “Data Directory: Hourly Data 2002-2017” online: Independent Electricity System Operator.

2. Not all of Ontario’s generation capacity is available at all times of the day or year.

Solar generation is low on cloudy days, natural gas plants lose efficiency under hot conditions, and nuclear plants need to be shutdown for maintenance. For these scenarios and more, the province needs to have a good mix of generation options and backup to reliably supply electricity to Ontarians.

3. Electricity generation must be sufficient at all times to meet regulated requirements.

The 2003 blackout demonstrated that an issue in one part of a regional electricity system can easily cascade into a large event. Being part of an interconnected northeastern electricity grid, Ontario must meet a cross-jurisdictional mandate to ensure the adequacy of its portion of the grid, including implementing a reserve margin (about 18% over and above its own highest capacity), to be able to respond to unexpected events.

Ontario’s electricity supply going forward

Ontario now has an adequate electricity supply to meet its demand at all hours of the day – but this situation could be short-lived. Electricity demand will need to increase if we are to lessen our reliance on fossil fuels and reduce our greenhouse gas emissions, and the province’s large nuclear plants will go offline for refurbishment in the next few years, making electricity conservation even more crucial. To learn more about the steps that Ontario has taken to improve the reliability of its electricity supply, please see Q5 of Making Connections.

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