Toronto Mayor David Miller and residents in the city's east end have lost their fight to stop a large power plant from being built on Toronto's waterfront.

The Ontario Power Authority inked a deal last week to purchase power from the Portlands Energy Centre, which will see the construction of a 550-megawatt gas-fired generating station on the shore of Lake Ontario.

The $730-million plant will be located near downtown Toronto in the city's Portlands district, close to the now-defunct Hearn generating station.

Officials refuse to say how much the owners of the generating plant, TransCanada Energy Ltd. and Ontario Power Generation, will receive for the electricity they produce, saying that's commercially sensitive information.

One source told CBC that the government has guaranteed them a fixed return every month. If electricity prices rise, the company will receive less of a subsidy, and if the price falls, the owners will get more.

The owners expect to make a seven to eight per cent return on their investment, the source said.

Mayor David Miller had thrown his support behind a rival bid by Constellation Energy, hoping a smaller plant would be built in the area and the difference in energy would be made up through conservation.

Miller and area residents wanted to see the area developed as housing and parkland.

However, the agency managing the province's power supply, the Independent Electricity System Operator, warned that Toronto faces rolling blackouts as early as the summer of 2008 if the city fails to find new energy sources.

The generating plant is scheduled to begin running at half the generating capacity, about 330 megawatts, by the summer of 2008.

It will be shut down that winter while construction is completed, then reopened the following summer as a fully operational 550-megawatt station.