CALGARY -- Wind power, often called a laudable but expensive energy source, may actually cost less than half the price of traditional coal-fired electricity when health and environmental costs are considered, a U.S. study has found.

The report published in today's issue of the journal Science calls for government promotion of this largely untapped yet emissions-free energy resource. That may in turn spur private investment in wind power, the authors said.

"Shifting from coal to wind would address health, environmental and energy problems," wrote Mark Jacobson and Gilbert Masters, both civil and environmental engineering professors at Stanford University in California.

Coal-powered energy costs between 3.5 and 4 cents (U.S.) a kilowatt-hour, according to the U.S. Department of Energy. But once factors such as smog, global warming and respiratory diseases are included, the price jumps to between 5.5 and 8.3 cents a kilowatt-hour, the authors found. That compares to between just 3 and 4 cents a kilowatt-hour to generate pollution-free electricity from large wind turbines, according to the study.

In assessing the social costs, the authors included, for example, the U.S. federal black-lung-disease benefits program, which has cost that country $35-billion since 1973. Black lung is caused by the long-term inhalation of coal dust.

Alternative-energy proponents said they are not surprised by the study, but that it does not mean high-tech windmills will start going up around the world.

"From the point of view from society as a whole, sure, wind's a lot cheaper. But the utility [company] doesn't care about society as a whole," said Jack Gibbons of the Ontario Clean Air Alliance.

The wind-power capacity appears to reflect that sentiment in some countries.

Last year, less than 1 per cent, or 140 megawatts, of Canada's power supply was wind-generated. That compares to the United States, where 2,554 megawatts, or less than 0.1 per cent, of the nation's electricity supply was wind-generated. Meanwhile, Denmark produced 14 per cent -- 2,300 megawatts -- of its domestic energy supply from the wind and Germany -- the world wind leader -- produced 6,113 megawatts last year.

(One megawatt, or a single large wind turbine, would produce enough electricity for about 1,000 average Canadian homes.)

Critics of traditional so-called dirty-energy sources say governments need to step in to encourage green energy if they want to avoid the long-term costs the U.S. study outlines.

In the United States, federal tax breaks are available for every wind farmer. And as electricity deregulation moves forward, quotas for renewable energy have been established at the state level.

Canada, however, has no comprehensive scheme to support wind power, said Andrew Pape-Salmon, director of the sustainable-energy program of the Alberta-based Pembina Institute.

"If there is one single thing we could do in Canada to support wind, it would be to create a financial mechanism in the marketplace or through government that recognizes the social and environmental values of wind," he said.

The Ontario Clean Air Alliance has proposed that strict emissions caps be placed on coal plants as a way to phase them out, force the development of cleaner energy sources and make wind power economically attractive.

Otherwise, Mr. Gibbons said, the wind-power costs calculated in the study are not realistic for new turbines to go up in Ontario. He pegs the cost in the range of 10 cents (Canadian) a kilowatt-hour.

Still, he said, the U.S. study could have an impact around the world.

"For governments that want to do the right thing, it certainly gives them the ammunition to justify their case and to help stand up to the industry lobby."