Last October, we reported that Apple was secretly clearing land in North Carolina for an unknown sized solar array to power its mammoth $1 billion, 500,000 square-feet data center there.

Now we know more. In Apples "Facilities Report: 2012 Environmental Update," it says the data center will be surrounded and partially powered by a BIG 20 megawatt (MW) solar system spanning 100 acres.

The system, which comes online this year, is Americas largest solar array dedicated to powering an end user (as opposed to a utility solar array).

Also powering the data will be a 5 MW fuel cell installation which runs on biogas, the "largest non-utility fuel cell installation in the US.

The data center is certified LEED-Platinum. "We know of no other data center of comparable size that has achieved this level of LEED certification," says Apple. 

Some of its energy-efficient design elements are:

• A chilled water storage system to improve chiller efficiency by transferring 10,400 kWh of electricity consumption from peak to off-peak hours each day
• Use of "free" outside air cooling through a waterside economizer operation during night and cool-weather hours, which, along with water storage, allows the chillers to be turned off more than 75% of the time
• Extreme precision in managing cooling distribution for cold air containment pods with variable-speed fans controlled to exactly match airflow to server requirements from moment to moment
• Power distributed at higher voltages, which increases efficiency by reducing power loss
• White cool-roof design to provide maximum solar reflectivity
• Real-time power monitoring and analytics during operations

Greenpeace, which last year placed Apple at the bottom of the list for its industry because of its "dirty" data centers in "How Dirty is Your Data Center, didnt even rate Apple in its recent Cool IT Leaderboard," because "it hasnt demonstrated leadership or elected to pursue market opportunities to drive IT energy solutions that many of its competitors have, despite record profits and large cash reserves."

Last week, we reported that North Carolina is becoming a hotbed for solar because of its supportive policies, but it still has one of the dirtiest energy mixes in the country, with only 4% of electricity coming from renewables (coal (61%) and nuclear (30.8%).

Greenpeace points out that Apples North Carolina data center could consume up to 100MW of power, about the amount to supply 80,000 U.S. homes, and most of that will still come from dirty energy.

Beyond that, Apple says in its report that only 2% of it total greenhouse gas emissions comes from corporate facilities. The vast majority is produced by manufacturing, transporting and use of its products made in the now infamous Foxconn in China. 

Apple says its goal is to achieve net zero energy for corporate facilities worldwide. Facilities in Cork, Ireland, Munich, Germany,  Austin, Texas, and Elk Grove, California run 100% on renewable energy, they say.