Maybe the future of climate friendly energy won't have as much to do with wind and solar energy as current booms in those technologies suggest.

Clouds and calm days could make the alternative energy stars bit players in a clean power future where round-the-clock dependability is critical.

That was one message from Microsoft Corp's deep thinker, Chief Research and Strategy Officer Craig Mundie, whose view stirred controversy among energy executives.

We should undoubtedly increase research and investment in alternative and renewable energy resources such as wind and solar but equally we need to be clear, at least in my mind, that I don't think these are ever likely to be a substitute for today's primary resources, particularly if world demand at least doubles over the next 20 years, Mundie said in a speech to utility executives this week.

As the world rushes to combat climate change, developing wind and solar power have become top priorities, since they do not produce carbon dioxide or other gases which stoke global warming. But neither works around the clock -- solar panels shut down at night and windmills only work when wind blows.

Wind accounted for 42 percent of new power installed in the United States last year, just behind natural gas's 46 percent. There is enough wind for the resource to one day supply 20 percent of all U.S. generation, American Wind Energy Association Utility Program Manager Jeff Anthony said.

But it's not just a question of when the wind blows.

Steve Snyder, president and chief executive of Canada's TransAlta Corp. aims to cut his firm's dependence on carbon-heavy coal to 5 percent of power by 2025 from about 50 percent today. The switch will mainly be a move to natural gas, and coal use could ramp up again if technology succeeds in economically cleaning carbon out of coal smoke.

Both wind and solar use huge amounts of land, and solar in particular really is economic in the southern latitudes. So here in the northern latitudes it's not just amounts of daylight, it's the intensity, Snyder said in an interview.

COAL FOR SOLAR

But the largest U.S. coal burner sees a bright future for solar. It's short-sighted to say it can't be baseload, said Dennis Welch, executive vice president for environment at American Electric Power Co Inc, known as AEP.

Dependable sources of power are called baseload, as opposed to peak demand plants -- often called peakers -- that can ramp up and down when needed. Solar works best at midday during peak demand, but like wind it is seen as intermittent.

Wind and solar can be baseload once the storage exists, said Welch, who said that AEP's trials of batteries to smooth availability worked technologically -- but were too expensive.

If grids of wind and solar were linked over vast distances, gusts in Colorado could be used to help California get through a cloudy patch, but people don't like to look at power lines.

Support for wind energy is not support for transmission, Peter Delaney, chairman, president and chief executive of Oklahoma utility OGE Energy Corp, told the conference.

U.S. regulation being considered could make it economically viable for his utility to aim for 20 percent wind by 2020. Before we were dealing with mandates that looked like our optimal amount was 10 to 12 percent of our capacity, he said.

The answer to solar and wind's future will be tested in Hawaii, which has one of the most aggressive clean energy goals. Overwhelmingly dependent on oil today, it aims to get 40 percent of its power from renewable sources by 2030.

Dick Rosenblum, president and chief executive of Hawaiian Electric Co, dismissed the idea that solar, wind, even wave energy would not be significant power sources. I don't think that's true at all, he told Reuters.

But we're going to have to do a fair amount of technological work to be able to integrate them successfully so that their intermittency is not visible to our customers because our customers want their lights on all the time, he said.

Like Mundie, he saw utilities gaining the ability to moderate demand as homes became smarter -- so a refrigerator could be turned up few degrees for a few minutes when clouds moved in and the utility started up a natural gas plant.

But he also said that the future would be one of many, many fuels -- not just the top two so far. Biomass, geothermal, even fuel-producing algae are the future, he said.

(Reporting by Peter Henderson; Additional reporting by Braden Reddall and Bernie Woodall; Editing by Richard Chang)

(For more environmental news see our Environment blog at blogs.reuters.com/environment)

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