It looks like just a small thing — an accounting change that led to a boost of $15.1 million in depreciation and amortization expense for Great River Energy last year.

Yet there was nothing trivial about it. Depreciation is up mostly because Great River decided changes in carbon emissions rules may make its biggest coal-fired power plants in North Dakota worth nothing by 2028. The biggest one had been expected to last until 2042.

"We are the first utility in the nation to do that," said David Saggau, Great River's CEO. "I am not aware of any others."

The evolution of carbon rules over the next 15 years is, really, anybody's guess. But responding now certainly seems like good thinking.

It also illustrates just how long-term the thinking has to be for power companies, and why the past few years have been challenging for them. Shortening a depreciation schedule to 2028 may not look like much of a decision in industries with almost daily technological change. On the other hand, most folks don't have to make decisions today on an asset that's meant to be used 45 years after they retire.

About 1.7 million people in our region depend on Great River making good choices for their electric power, too. Based in Maple Grove, Great River is one of those unusual companies that's both really big — about $1 billion in annual revenue — and low profile. It has no retail customers, generating and distributing electricity for 28 member electric cooperatives from northeastern Minnesota to the Iowa border.

Saggau said any conversation in December 2009 "would have filled the newspaper" with the challenges companies like his faced.

The Great Recession derailed the plans of nearly everyone, of course, but for power companies it takes years to plan and build a big power line or generating plant. It's almost impossible to start too early on a project if new capacity may be needed.

Before the recession, the worry was about capacity for growth. Saggau said Great River was forecasting an eventual need for 600 more megawatts of what's called "base load" generating capacity, meaning the minimum power that's needed every day.

Traditional thinking would have meant seeking permission, and the capital, to build a really big power generating station, maybe 800 megawatts. Instead, Great River decided on smaller ones. Great River broke ground on the first, Spiritwood Station, in North Dakota in 2007 — just as the ­economy was about to tumble into the Great Recession.

By the time construction on this 99-megawatt plant was all but finished, its capacity just wasn't needed. There was some grumbling among member customers about mothballing a new plant, but it certainly looks smarter than mothballing one eight times larger.

Spiritwood wasn't just a power generating station, either. It was designed as a combined heat and power facility. The idea was to use as much heat out of the coal being burned as possible, by piping steam to adjacent users.

Financing for an ethanol plant next door was derailed by the financial crisis. Great River Energy then decided it had to build it to make the whole operation more efficient. The power station went on the grid officially in November, and the ethanol plant will be operating next year.

Saggau, who was promoted to the top job in 2005 after a career in legal and regulatory affairs, attributes a lot of the careful decisions of the recent past to Great River's cooperative ownership structure.

Great River's board is made up of members from the 28 cooperatives. It meets monthly.

About two weeks after every board meeting is another meeting of the managing officers of the member cooperatives. And what this group of executives really cares about is the wholesale cost of electricity, closely followed by reliability.

Saggau used to work on "rate cases" for an investor-owned utility, the periodic application to a state's regulator to approve an electric rate increase. With the meeting schedule at Great River, he more or less now has two of them every month.

"Like a lot of co-ops, our wholesale power costs represent about 60 percent of our budget," said Robin Doege, CEO of Todd-Wadena Electric Cooperative and incoming chair of Great River's member managers group. "We like to see Great River Energy do things in a cost-effective manner. And it's been challenging."

The good news is that Great River now doesn't anticipate building more central station generating capacity for at least 15 years. As Saggau put it, "the incremental cost of new generation is so much higher than our embedded cost that we would just as soon not ever build anything more."

In addition to promoting ways to slow power usage growth, the company embarked on a program to install 19 solar projects throughout the state. Figuring out how to efficiently add generating capability like solar in its network is a priority.

Another problem, of course, is efficient power storage. On a recent December morning, a visitor to the Maple Grove headquarters could just about touch the clouds. The big solar arrays there were not throwing off much power.

Saggau said the challenge of efficiently storing power generated from intermittent sources such as solar and wind will be met. He simply doesn't know how.

He sounded pretty optimistic about the potential for electric cars, with their big banks of batteries that can be charged overnight when the wind is blowing and generating electricity is cheap.

He's less optimistic about clarity coming to emissions rules and other aspects of energy policy.

It's difficult to decide what to build for 2029 and beyond, he said, when underlying energy policy is fluid and can change rapidly. "We can manage to any certainty, Saggau said. "We just can't manage to uncertainty."

Actually, the record seems to show that the company probably does just fine with a little uncertainty.

lee.schafer@startribune.com • 612-673-4302