TORONTO - Ontario's electricity transmission giant is launching the largest expansion to the province's transmission system in 20 years which will give it access to enough electricity to power about 1.5 million homes by 2011.

Hydro One said it will spend $600 million to expand the transmission system between the Bruce power plant and a switching station in Milton, Ont.

Energy Minister Dwight Duncan said Monday the expansion will help boost the province's accessible renewable and nuclear electricity supply from the Bruce region by 3,000 megawatts.

The new line will help the province tap into renewable energy projects underway in the region, as well as into two nuclear reactors at Bruce Power which are scheduled to go online in 2009.

"It gives us a real opportunity for a lot more cleaner, greener power that will be emissions-free," he said. "This is the largest transmission project we've done in 20 years."

The 180-kilometre expansion, which is still subject to environmental assessments and the approval of the Ontario Energy Board, is expected to be completed by December 2011.

The plan also affects about 400 properties along the 180-kilometre corridor but Duncan said only 30 of those are impacted in a "profound way."

"It's already along an existing hydro corridor," he said, adding consultations with landowners will begin shortly.

Shawn-Patrick Stensil, energy campaigner with Greenpeace, said the province has left itself little wiggle room to complete the transmission line.

According to documents obtained by Stensil under a freedom of information request, the government signed a deal with Bruce Power which could leave taxpayers on the hook for $1 billion in penalties.

"The government signed this deal ... knowing they didn't have enough transmission capacity," he said. "There is no saying they're going to do it in time."

With tight deadlines, Stensil said the government will likely skimp on much-needed public consultations.

The government said the new transmission lines will carry clean, renewable energy, but Stensil said it will primarily transmit nuclear-generated power to the Toronto area.

Acting CEO Laura Formusa said in a statement that Hydro One "is sensitive to concerns of property owners, aboriginal communities, local municipalities and stakeholders impacted by the project."

"(We) will work to ensure that we manage their concerns in a manner that is fair and responsible," she said.

The announcement comes the same day as the Ontario Power Authority recommended Hydro One move forward with the expansion.

In a report last fall, the authority said a new line was required to tap into the increased energy production from the Bruce region.