Exactly when the unit will come back online is not known at this point, though media reports suggest the unit will return in about a week.

The 880 MW combined cycle Goreway station, which entered service in 2009 and cost more than $1 billion to build, uses natural gas to turn combustion turbines to generate electricity.

Combined cycle plants increase efficiency by blending two methods for generating electricity.

The first cycle burns a fossil fuel, such as natural gas, directly into a gas turbine that generates power.

The second cycle uses waste heat from the first cycle to boil water, and the resulting steam is used to turn a turbine that also produces power.

Compared to a coal-fired plant, the facility generates 97 per cent fewer noxious gases and next to no sulfur emissions.

Sithe sells the power from Goreway to the province's Ontario Power Authority under a 20-year purchase agreement.