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The government agency that manages the supply and demand of electricity in Ontario is preparing for an 800-megawatt drop in power consumption during Earth Hour – the equivalent of turning off eight million household light bulbs or shutting down a medium-sized coal plant.

It also works out to about 4.25 per cent of total electricity consumption in the province, compared with what we consumed last Saturday between 8 p.m. and 9 p.m.

But Paul Murphy, chief executive officer of the Independent Electricity System Operator, said it’s impossible to predict with precision exactly how much electricity consumption will be cut as Ontarians voluntarily go dark tonight.

"We haven’t had anything like this before in the province," said Murphy, though he assured that it’s part of his agency’s job to anticipate hour-to-hour changes in electricity use. "The difference here is that it won’t follow the normal Saturday night pattern."

Following patterns plays a huge role in forecasting, but just as important is keeping an eye on special events that could lead to sudden spikes – or unexpected drops – in electricity demand.

A classic example is Tiny Tim’s Dec. 17, 1969, wedding on The Tonight Show Starring Johnny Carson. What amounted to a publicity stunt unexpectedly attracted 40 million viewers, causing an abnormally high number of power-hungry television sets to be turned on and a spike in electricity demand.

The final episode of M*A*S*H in the late 1980s and the funeral of Princess Diana in the late 1990s also caused power swings. Television events such as these commonly lead to anomalies in power use, which can amount to as much as 100 megawatts during commercial breaks when viewers open and close their fridges to get a drink.

A million fridge lights going on, or a million toilets flushing, can collectively suck up a lot of electricity – the latter at pumping stations no fax payday loan. Playoff games in professional sports are also disruptive of typical power-consumption patterns. "At least when the Leafs are in the running," said Murphy.

And it’s not just TV – weather is also an important consideration. Something as simple as a large cloud moving over the GTA can potentially, during the day, shed tens of megawatts in demand from the system.

There are two general approaches to balancing power needs as Earth Hour kicks in, Murphy explained. If the drop in electricity consumption is gradual, as it was in Sydney, Australia, when it participated in Earth Hour last year, then it’s possible that less coal-fired power will need to be dispatched.

If the drop is sharp, then the system operator may have to rely on its hydroelectric plants, which, compared with other sources of generation, can be called into action or taken offline much more quickly. The same reasoning applies at the end of Earth Hour, when there could be a sudden spike in lights going back on.

Murphy assured that the system is designed to accommodate any scenario, and that beyond keeping a closer eye on Earth Hour itself, he expects tonight to be a typical evening for his staff. As for making a more accurate prediction in 2009, he said, "after this year we’ll have a better idea."

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