While Apple partially powers its North Carolina data center with coal, that facility will operate exclusively on renewable energy by the end of the year, the company says.

The tech giant based in Cupertino, Calif., vowed this month to do the same for the data center it’s building in Prineville.

A few miles away from its 20-megawatt data center in Maiden, N.C., Apple is building what it calls the largest privately owned solar installation in the country, with two 100-acre arrays capable of generating 84 million kilowatt hours per year.

Biogas-fed fuel cells near the data center will contribute an additional 40 million kilowatt hours per year.

Between the fuel cell and the solar installations, Apple will generate on site 60 percent of the energy it will need in order to store, send and receive information from users of its iCloud and other digital services. Apple will buy the rest of the energy it needs for the data center from local and regional sources, according to its website.

Apple announced on May 15 that it would exclusively use renewables for its Maiden data center, two days after the environmental group Greenpeace staged protests in Cupertino over Apple’s use of power in North Carolina from Duke Energy, most of which comes from coal.

“All three of our data centers will be coal-free, which is an industry first for anybody of our size,” Peter Oppenheimer, Apple’s chief financial officer, told Bloomberg News, referring to its data centers in Prineville, North Carolina and Newark, Calif.

Greenpeace in 2010 brought up the same issues about Facebook’s planned partial use of power from coal at its data center in Prineville, across the highway from Apple’s future data center site. A solar array was running when Facebook officially opened its data center in April 2011.

Apple purchased 160 acres for its Prineville data center in February. It “will be every bit as environmentally responsible as our Maiden data center,” Apple states on its website.

“At Prineville we have access to enough local renewable energy sources to completely meet the needs of the facility.”

So far, though, it’s unclear exactly how the company will do so.

Apple spokeswoman Kristin Huguet declined to comment.

But plans for Apple’s North Carolina facility could suggest how the company will power its operations with renewable energy in Central Oregon.

In addition to Apple’s North Carolina data center, other facilities it has in Austin, Texas; Elk Grove, Calif., Munich; and Cork, Ireland, all run off renewable energy sources, the company said in a report released earlier this year.

The push to run data centers on renewable energy has increased among American companies in the past three or four years, said William Tschudi, an employee in the Environmental Energy Technologies Division of the Lawrence Berkeley National Laboratory in Berkeley, Calif.

“Some companies, like Intel, claim to have most, if not all, of their energy supplied by green sources,” Tschudi said. “Some companies are being really aggressive about that.”

BendBroadband’s 30,000-square-foot Vault data center in Bend, which opened last year, runs with zero carbon emissions, thanks to a solar array, an efficient cooling system and purchases of carbon offset credits and Pacific Power’s Blue Sky renewable-energy program.

Apple uses a similar three-pronged approach to reach its goal of net-zero energy use: generating renewable energy on site, buying renewable energy elsewhere and minimizing the amount of energy its equipment needs.

Under a sunlight-reflecting white roof, the North Carolina facility uses motion sensors for lights and variable-speed fans for servers, among other energy-conserving tools. It also takes in cold air from outside to cut down on using its chillers to keep servers cold, just as Facebook does at its Prineville data center, less than a mile away from Apple’s.

Facebook has said the dry, cool air in Central Oregon was one motivating factor for locating in the region.

Details are not yet publicly available for Apple’s Prineville data center. But according to its website, the company will buy geothermal, hydroelectric and wind power from two utility companies.

Geothermal potential could be as close to Prineville as Powell Buttes. A handful of geothermal exploration wells were drilled on the buttes in 1980, according to records from the state Department of Geology and Mineral Industries.

Companies continue to apply to generate hydroelectric energy in Central Oregon. South of Prineville, Portland General Electric has expressed interest in installing a hydroelectric unit at Bowman Dam, although the presence of a wild and scenic river boundary has blocked the project.

And wind power could be available about 30 miles south of Prineville, where the 104-megawatt West Butte Wind Power Project was approved last year.

In addition, utilities and other companies operate or have proposed 29 wind farms in Gilliam, Morrow and Sherman counties about 150 miles north of Prineville, according to a list from Renewable Northwest Project, a nonprofit in Portland.

Between 2006 and 2011, Portland-based PacifiCorp, Pacific Power’s parent company, increased its wind-power capacity by more than 1,400 megawatts, according to a handout from the utility. Ninety percent or more of the power Redmond-based Central Electric Cooperative Inc. provides comes from the Bonneville Power Administration’s hydroelectric facilities, said CEC’s member-services director, Jeff Beaman.

In the immediate area of the Prineville data-center facility, Apple has 160 acres to use, although an unmanned 2-megawatt, 9,300-square-foot data center is being built now. At least one more building will be constructed, if Apple is to hire 35 workers by December 2013, as outlined in its enterprise zone application.

Apple could build renewable-power generators on its Prineville land, as it is doing in North Carolina. It would need more land than it owns now to locate two 100-acre solar arrays, as it’s doing in North Carolina.

However, a company would pay about 1 cent less per kilowatt hour of solar energy in Central Oregon than it would in the middle of North Carolina, according to an estimate using a performance calculator from the National Renewable Energy Laboratory. The calculator takes into account monthly solar radiation, the angle of solar panels, array size and other factors.

Assuming the same amount of solar generation in Prineville, that one penny’s difference could add up to an $840,000 savings per year.

“Central Oregon is a wonderful resource for renewable energy. We obviously have sunshine,” said Paul Israel, president of Bend-based Sunlight Solar Energy, which installed solar panels for Facebook and BendBroadband’s Central Oregon data centers.

But one incentive for investing in renewable energy has been drastically reduced.

The money available for state tax credits for renewable-energy projects fell last year from $300 million to $1.5 million per year, according to The Bulletin’s archives. The change could decrease the appeal of building a project, Israel said.

“If Apple has the appetite and the financial wherewithal, then, yes, we probably do (want to bid) on it, design it and build it,” Israel said.