"I think it's time to stop burning coal in Ontario, switch on to harnessing the power of the wind and the sun, as they've been doing in so many other parts of the world for decades," said McGuinty.
He also warned that scrapping such a huge contract could end up costing taxpayers a lot of money.
"They're being reckless with our tax dollars," he said.
PC Leader Tim Hudak tried unsuccessfully to get Energy Minister Brad Duguid to say exactly what, if any, penalty could be imposed for scrapping the Samsung deal.
McGuinty said wind and solar power account for what he calls a minuscule 3.2 per cent of electricity bills.
Samsung is investing at least $40 million to convert a former machining plant into a facility for making wind towers, as part of a province-wide deal with the Korean company. About 300 people will work there.
The premier's visit comes days after Hudak said he would kill the Samsung deal if his party wins the October election.
Finance Minister Dwight Duncan said the gloves are off.
"We're going to fight him on the closure of this plant, we're going to fight him on the elimination of the Green Energy Plan, and we're going to fight the lies he's putting out in the absence of his own platform," said Duncan. "We think it's wrong, we think it's dangerous to the province's future."