"We will become the largest green power consumer of any municipal government in Canada," Bronconnier said. "This is a landmark agreement and demonstrates our global leadership in reducing the impact of electricity generation on the environment."
The switch from coal-fired power plants to renewable energy will cut the city's greenhouse gas emissions by about seven million tonnes over 10 years, said the city.
The city has a target to bring corporate greenhouse gas emissions down to 50 per cent of 1990 levels, which were about 460,000 tonnes, by 2012.
Calgary's C-Train system already runs entirely on power generated from the wind.
"Alberta could go from 70 per cent coal-fired electricity, which is what we have today, to 70 per cent clean electricity in 20 years, so we have a significant renewable energy potential in the province," said Alex Doukas from the Pembina Institute.
"This is a great step that the city of Calgary is taking to push us towards that green energy future in the province."
The agreement will cost taxpayers $10 million a year for 25 years. Enmax plans to use the $250 million to build more wind farms to increase the long-term supply of green power. Enmax already has ownership in three wind farms in southern Alberta.
But the cost of the Calgary deal concerns at least one alderman.
"We were told that over the life of the contract it wouldn't cost any more to buy green electricity than it would brown, so I think that needs to be monitored," said Ald. Ric McIver.
City operations, which used about 400,000 megawatt hours in 2008, are expected to increase electricity consumption by about 40 to 50 per cent over the 25-year term of the agreement.