TORONTO -- It's as if the COVID-19 epidemic had tripped a circuit breaker, shutting off all power to a city the size of Ottawa.

Virus-induced restrictions that have shut down large swaths of normal commercial life across Canada has led to a noticeable drop in demand for power in Ontario, insiders said on Friday.

Terry Young, vice-president with the Independent Electricity System Operator, said planning was underway for further declines in usage, given the delicate balance that needs to be maintained between supply and demand.

"We're now seeing demand that is running about 1,000 to 2,000 megawatts less than we would normally see," Young said. "You're essentially seeing a city the size of Ottawa drop off demand during the day."

At the high end, a 2,000 megawatt reduction would be close to the equivalent peak demand of Ottawa and London, Ont., combined.

The decline, in the order of 10 per cent from the 17,000 to 18,000 megawatts of usage that might normally be expected, began last week, Young said. The downward trend became more noticeable as governments and health authorities ordered non-essential businesses to close and people to stay home. However, residential and hospital usage has climbed.

Experts say frequent hand-washing and staying away from others is the most effective way to curb the spread of the highly contagious coronavirus, which poses a special risk to older people and those with underlying health conditions. As a result, factories and other big users have reduced production or closed entirely.

Because electricity cannot be stored, generators need to throttle back their output as domestic demand shrinks and exports to places such as the United States, which is also being hit hard by the coronavirus, fall.

 "We're watching this carefully," Young said. "We're able to manage this drop, but it's something we obviously have to keep watching...and making sure we're not over-generating electricity."

Turning off generation, especially for nuclear plants, is an intensive process, as are restarts and would likely happen only if the downward demand trend intensifies significantly. However, one of North America's largest generators, Bruce Power near Kincardine, Ont., said it had a large degree of flexibility to scale down or up.

"We have the ability to provide one-third of our output as a dynamic response, which is unique to our facility," said James Scongack, an executive vice-president with Bruce Power. "We developed this coming out of the 2008 downturn and it's been a critical system asset for the last decade."

The upshot, Scongack said, is that the nuclear plant can ramp production from each of its eight reactors down and then up by 300 megawatts -- 2,400 megawatts in total -- in relatively short order.

"We don't see there being a scenario where our baseload will not be needed," he said.

The province's publicly owned Ontario Power Generation said it was also in conversations with the system operator, which provides direction to generators.

One clear shift in normal work-day usage with so many people staying at home has been the change in demand patterns. Typically, Young said, there's a peak from about 7 a.m. to 8 a.m. as people wake and get ready to go to work or school. The peak is now occurring later in the morning, Young said.

This report by The Canadian Press was first published on March 27, 2020