Apple has revealed new details about the operations of its huge data center in Maiden, North Carolina, including plans to build a 20-megawatt solar power facility to support its operations. Apple also plans to use a fuel cell powered by biogas that could generate up to 5 megawatts of power.

The Apple facility would be the largest solar array dedicated to data center operations, surpassing a 14 megawatt array being built to support the McGraw-Hill data center in East Windsor, New Jersey. Apple disclosed its renewable energy ambitions in Maiden in the company's latest environmental report.

Although Apple's solar plans are making headlines, the report also sheds light on many aspects of Apple's data center operations. Until now, the company has made general statements about the efficiency of its data center, without discussing specific techniques used within the facility. Apple's approach includes:

Apple uses a "free cooling" system that employs water-side economization, in which cool outside air is incorporated into a heat exchanger to supply cold water for the data center cooling systems. The company estimates that it will be able to use the economizer system for about 75 percent of the year.

When it is too warm to use the economizer, Apple will use a chiller, a large system that refrigerates water for use in cooling servers. Apple will use a chilled water storage tank to reduce its power bill by running the chillers at off-peak hours, when electricity rates are cheaper. Chilled water from the storage tank can then be used during peak hours, reducing the overall energy cost.

Apple says it is using a high-voltage power distribution system, which increases efficiency by reducing power losses due to conversions to step the power down within the data center. Similar designs have been used by Google and Facebook in their data centers.

Apple is using containment "pods" in which airflow is regulated using variable speed fans, allowing the company to closely match the fan speed to the temperature and pressure inside the containment area.

None of these technologies are new, but they represent important best practices in the operation of large-scale facilities like Apple's 500,000 square foot first phase in North Carolina. "Our new data center in Maiden, North Carolina, demonstrates our commitment to reducing the environmental impact of our facilities through energy-efficient, green building design," the company said in its environmental statement (PDF).

Apple disclosed that the facility has earned Platinum, the highest level attainable under the LEED ( Leadership in Energy and Environmental Design) rating system for energy efficient buildings. The company used 14 percent of recycled materials in its construction process, and diverted 93 percent of construction waste from landfills. Apple also sourced 41 percent of purchased materials within 500 miles of the Maiden site, which reduces the environmental impact from trucking materials over long distances.

"We know of no other data center of comparable size that has achieved this level of LEED certification," the company said. "Our goal is to run the Maiden facility with high percentage renewable energy mix, and we have major projects under way to achieve this — including building the nation’s largest end user-owned solar array and building the largest nonutility fuel cell installation in the United States."

Apple said the 5 megawatt fuel cell facility, located adjacent to the data center, will be powered by 100 percent biogas, and provide more than 40 million kWh of baseload renewable energy annually. The facility will be among the largest data center initiatives using fuel cells, Last year AT&T said it would install Bloom Energy fuel cells at 11 sites in California to generate 7.5 megawatts of power. A T-Systems data center in Germany has been using biogas in a fuel cell in its data center since 2009, and a similar system is being used by Infinity in the UK. The primary barrier to use of fuel cells in data centers has been the economics and the up-front cost of the units.