Apple says it will use 20 megawatts of power at full capacity in its North Carolina data center, about one-fifth the amount estimated by Greenpeace in a report that is sharply critical of Apple and other data center operators for relying upon "dirty" energy sources to power their cloud computing operations.
Apple's statement raises questions about the credibility of the estimates in the Greenpeace report, and illustrates the difficulty of seeking to estimate data center power usage - a detail that many companies are unwilling to disclose on their own.
Greenpeace has estimated that Apple will use 100 megawatts of power at the facility in Maiden, North Carolina. Greenpeace's Gary Cook used that estimate to downplay the significance of Apple's substantial investment in on-site renewable power in Maiden, which includes a 20 megawatt solar array and a biogas-powered fuel cell with a 5 megawatt capacity.
"While much has been made of this announcement, it will cover only 10 percent of their total generation for the data center," Greenpeace said in its report, How Clean is Your Cloud?, which has received widespread media attention today. But Apple says that isn't the case at all.
"Our data center in North Carolina will draw about 20 megawatts at full capacity, and we are on track to supply more than 60% of that power on-site from renewable sources including a solar farm and fuel cell installation which will each be the largest of their kind in the country," Apple said in a statement. "We believe this industry-leading project will make Maiden the greenest data center ever built, and it will be joined next year by our new facility in Oregon running on 100% renewable energy."
Greenpeace has also assumed that Apple would use coal-sourced power in its Prineville, Oregon data center and factored that assumption into its Clean Energy Index ranking of 15.3 for Apple, far below the scores given to Facebook (36.4), Google (39.4) and Yahoo (56.4).
Apple would clearly receive a much higher score if Greenpeace used a 20 megawatt base to evaluate its coal-sourced power. In effect, the current score whacks Apple for 80 megawatts of "dirty" power that it's not using.
So how could Greenpeace have been so far off base? For its starting point, Greenpeace's math is based on the $1 billion Apple has said it will invest in the facility in Maiden, North Carolina. After Apple released its statement, Greenpeace's Cook posted a response:
"We made estimates of power demand using fairly conservative industry benchmarks for data centre investments: 1MW of power demand from servers for every $15 million, though the number is often closer to $8 million for many companies. Thus, a $1 billion investment should net Apple 66MW of computer power demand. Assuming a fairly standard energy efficiency factor for new data centres for non-computer energy demand of 50% gives you a 100MW data center. While Apple is well known for making more expensive consumer products, if Apple's plans for the $1 billion investment only generates 20MW in power demand, that would be taking the 'Apple premium' to a whole new level."
An obvious gap in that logic is that it doesn't account for Apple's investment in the solar array and fuel cell technology being built to support the iDataCenter - costs that are atypical for data center construction and not included in comparative metrics. In developing its clean energy index for Apple, Greenpeace appears to have failed to account for the cost of the company's clean energy.
Some approaches to data center power estimation use the square footage of the data center as a starting point. This can also result in apples-versus-oranges comparisons, as data center workloads can vary widely in the density of their compute infrastructure, which is guided by the applications the facility is supporting.
Data centers also use different amounts of space for non-compute infrastructure such as the power and cooling equipment. While Apple's Maiden data center is 500,000 square feet in total area, about 184,000 square feet of that is dedicated to data halls for servers, compared to 262,000 square feet of space supporting mechanical and electrical systems.