Peak demand is the fleeting surge in electricity usage that occurs generally on hot summer days when air conditioners are running full out. Peak demand is costly in two ways. First, Ontario often increases the use of dirty coal-fired generating stations to meet this surge in demand, making air quality even worse on some of our poorest air quality days. Second, building new power plants and transmission lines just to deal with demand levels that may last for less than 100 hours per year is extremely expensive. The proposed gas-fired peaking plant in Northern York Region, for example, is expected to cost approximately $365 million (for more on better solutions to meeting York Region's power needs, click here.) Reducing electricity usage in peak periods through conservation or shifting power consumption to off-peak periods is a far more cost effective solution.

What is driving peak demand?

Peak electricity demand on summer days is largely driven by air conditioning. with residential and commercial air conditioning systems consuming roughly 40% of our total electricity production in peak periods. Lighting is the next biggest use at approximately 13%. According to the Ontario Power Authority, it would cost up to $1.64 per kilowatt hour to meet this peak demand with new supply sources, roughly 16 times the cost charged to residential consumers. That's why reducing peak demand is not only good for our environment and health -- it is also good for our economy.

When does peak demand occur?

Ontario's peak electricity demand usually occurs on hot summer days when air conditioners are running full tilt. Demand is generally at its highest between 12 p.m. and 9 p.m.

The interesting thing about peak demand is that it is fleeting -- there were only roughly a dozen high peak demand days over the four warm weather months in 2008 and on each of these days, this high demand lasted for only a few hours. That's why it is far more effective to work to knock down these spikes in peak demand by conserving electricity and shifting some uses to off-peak periods than to try to meet this demand with increased electricity supplies or dirty coal.