"When you're importing power every day – especially on the days when you're dealing with peak... demand – it gets more and more and more expensive," Tory said after speaking to an audience in Sarnia, Ont.
"There is nothing wrong with importing power but there is something that is unwise about being reliant at all times on imports to keep the lights on."
The Liberals haven't done enough to make Ontario self-sufficient by building up the province's homegrown energy supply, Tory said. The province has less generating capacity now than it did 12 years ago, he added.
If the Conservatives win the Oct. 10 election, Tory said he will spend money to fix the province's aging nuclear plants and expand financial incentives to encourage conservation.
"We're operating right at the edge now," he said.
But Energy Minister Dwight Duncan said Tory "doesn't know what he's talking about."
Ontario now actually exports more energy than it imports and is in good shape this summer, Duncan said.
Any talk about Ontario being vulnerable to blackouts this summer is just "blowing smoke," he added. Even with the loss of two units at Pickering, Duncan said the province has more power this summer than it did last year.
"Mr. Tory should start telling the truth," Duncan said, adding the Conservatives have opposed virtually every Liberal attempt to expand Ontario's power supply.
"Now, all of a sudden, they've had their conversion on the road to Damascus. Good for them. It's just unfortunate they didn't do it seven years ago. If they had, we wouldn't have experienced a lot of what we've experienced."
The Liberals have vowed to close Ontario's coal-fired plants by 2014, using refurbished nuclear power to bridge the gap while the province invests in cleaner energy sources and conservation.
Keith Stewart, manager of the climate-change campaign at the World Wildlife Fund, said the province's energy system is less vulnerable than it was several years ago because the Liberals have brought more generation online.
But he said all parties should learn not to rely too heavily on nuclear power given its history of cost overruns and delays which have reduced the energy supply.
"It's a lesson we should learn and not do over," Stewart said.
NDP Leader Howard Hampton said the province should look at reducing its reliance on imported, dirty coal power.
But he said Ontario can only do that if it gets serious about energy efficiency and conservation – something he says the Liberals have failed to do in their four years in government.
"We have huge possibilities in terms of using... less electricity to accomplish the same social and economic ends."