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Who We Are The Power System Demand & Price Conservation Electricity Pricing in Ontario


The IESO is responsible for co-ordinating emergency planning for Ontario's power system.

The IESO and its market participants are required to plan for all types of potential emergencies and test these plans in annual drills. This planning process also includes working with Emergency Management Ontario to address public health and safety issues.

A power emergency can be caused by a variety of factors. An outage may take place as a result of problems with distribution or transmission systems, such as lightning or trees hitting the lines. If your lights do go out, contact your local utility. Most utilities have 24-hour outage information telephone lines that provide updates on the status of an outage and when power is expected to be restored.

In the event of a major outage or disruption in the power supply, the IESO can take a number of actions. These include:

  • Issuing a public appeal asking Ontarians to reduce their electricity use.
  • Directing certain large volume users to cut consumption.
  • Reducing the voltage of electricity on the transmission lines by 3-5 per cent. This stretches the available electricity to meet higher demand. A voltage reduction of this amount would not be noticeable by most consumers.

In extreme situations, the IESO would implement rotating blackouts. This involves cutting power to parts of the province for a short period of time on a rotating basis. These actions preserve the overall integrity of the power system, avoiding a system-wide outage.

The U.S.-Canadian Task Force that investigated the causes of the August 14, 2003 blackout confirmed that its cause did not originate in Ontario. The blackout resulted from rapidly cascading outages that began in Ohio as a result of a number of deficiencies in specific practices, equipment and human decisions. The IESO has been advocating mandatory reliability standards throughout the North American power system, similar to the ones already in place in Ontario.

The August 2003 blackout was a clear example, however, of the importance of maintaining that balance between supply and demand. Surges in power along the system caused the transmission lines to automatically disconnect so that equipment wouldn't be damaged. Then, IESO staff, working with generators, transmitters and local utilities, co-ordinated the restoration of the power grid, bringing the power back to communities as it became available. Throughout this process, demand for electricity had to be carefully balanced against the available supplies, to maintain the integrity of the system.

In the event of a power emergency, the IESO works closely with provincial authorities to ensure that the latest information is available to the public. This information is made available on this Web site and through the news media.

Public Appeals

There may be times when extreme weather or unexpected transmission or generation outages stretch the system's ability to provide enough electricity to meet demand and required reserves. Ontario's IESO has a number of options available to maintain reliability of the system. For example, we can arrange emergency imports of electricity and call on specific companies who have agreed to cut back on their electricity use on short notice. We may also choose to issue a public appeal to all businesses and consumers to reduce their consumption. The appeals help to smooth out spikes in demand during high-peak periods.

Weather conditions affect the demand for electricity considerably, which is why Public Appeals are often issued during extreme cold spells and heat waves. For example, each degree above 16°C creates an additional 380 MW of demand. And that's not counting the impact of humidity, which can also have a significant impact on demand.

Appeals to reduce consumption are issued to the news media. These appeals and tips on how to conserve energy are also posted on the IESO website.


Voltage Reductions

Public Appeal Archive

Energy Saving Tips

If a power outage does occur, your local utility will be able to provide you with up-to-date information about the affected areas and expected restoration times.

Effect of Weather on Demand for Electricity