TORONTO -- Ontarians will soon be paying more than twice as much for electricity during peak demand periods than off-peak times.

Starting May 1, the price for peak periods -- weekdays from 11 a.m. to 5 p.m. -- will be 16.1 cents per kilowatt hour, compared with 8 cents for off-peak hours on weekdays from 7 p.m. to 7 a.m., and all day on weekends and holidays.

The mid-peak rate of 12.2 cents a kilowatt hour will apply weekdays from 7-to-11 a.m. and from 5-to-7 p.m.

The Ontario Energy Board estimates the change to a 2:1 ratio between peak and off-peak rates will add $5.71 to the average household electricity bill.

But the board says the change to a higher peak rate gives consumers more of an opportunity to lower their electricity bills by doing laundry and dishes at off-peak times.

The opposition parties say Ontario's already high electricity rates will "go through the roof" if the Liberals proceed with their plan to sell 60 per cent of Hydro One, the province's giant transmission utility.