"Can Solar Reduce The Impact Of Two High-Profile Data Centers? Amazon Engineer Weighs In [Updated]"

Solar arrays may not be able to provide the power density needed by data centers, one expert argues. (Image credit: AFP/Getty Images via @daylife)

Solar power may be not be best way to reduce the environmental impact of sprawling data centers built by companies such as Apple and Facebook, James Hamilton, an Amazon vice president and distinguished engineer argued on his personal blog last Saturday.

“If we had $x dollars to invest in lowering datacenter environmental impact and the marketing department was not involved in the decision, I’m not convinced the right next step will be solar,” Hamilton wrote.

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The catch: Apple has said little publicly about how much power its Maiden, North Carolina data center uses. If Apple’s data center uses significantly less power than Hamilton estimates, the solar array at that facility is more efficient than Hamilton estimates — or both — then solar could become a useful tool for reducing the impact of

the growing number of data centers being built to support cloud services by companies such as Microsoft, Amazon, Facebook, Google, and others.

Hamilton, who has worked on both Amazon and Microsoft’s cloud-computing infrastructures, starts his analysis with a look at a small, experimental solar installation erected by Facebook at its Prineville, Oregon data center and a massive 171-acre solar array being built near Apple’s Maiden, North Carolina facility.

While Hamilton praised Facebook’s other efforts to run its data centers efficiently, he estimated the experimental 100 kilowatt solar array at Facebook’s Prineville, Oregon data center will contribute little to the facility’s energy needs (to Facebook’s credit, it has never represented otherwise).

“Using this solar panel output estimator, we can see that the panels at this location and altitude, yield an effective output of 13.75%. That means that, on average, this array will only put out 13.75 kilowatts. That would have this array contributing 0.055% of the facility power or, worded differently, it might run the lights in the datacenter but it has almost no measurable possible impact on the overall energy consumed….. As a point of comparison, this entire solar farm produces approximately as much output as one high density rack of servers consumes.”

Hamilton wasn’t very optimistic about the impact of a far larger solar array being built by Apple at its Maiden, North Carolina data center, either. Hamilton estimates the data center consumes at least 78 megawatts of power, but that Apple’s nearby solar array will only generate an average of 3.2 megawatts, or 4% of the data center’s typical needs.

“The solar array requires 171 acres of land which is 7.4 million sq ft. What if we were to build a solar array large enough to power the entire facility using these solar and land consumption numbers? If the solar farm were to be able to supply all the power of the facility it would need to be 24.4 times larger. It would be a 488 megawatt capacity array requiring 4,172 acres which is 181 million sq ft. That means that a 500,000 sq ft facility would require 181 million sq ft of power generation or, converted to a ratio, each data center sq ft would require 362 sq ft of land.”

While Apple wouldn’t comment on Hamilton’s estimate, Apple’s 2012 facilities report states Apple will meet “the energy needs of the Maiden facility with a high-percentage renewable energy mix,” and asserts Apple will increase the amount of renewable energy it uses as its data center expands: “Apple is committed to pursuing energy-efficient growth by increasing our renewable energy participation to match the growing needs of our data center.”

That mix includes both a solar array and a 5-megawatt biogas fuel cell installation. In its report, Apple asserts “[t]he facility is exceptionally energy efficient,” ticking off an array of power-saving features at the facility. If Apple can economically supply much of its data center’s needs with solar power, expect others building massive data centers to follow its lead.

This article has been updated with details from Apple’s 2012 environmental update.