Google has signed a 20-year purchase agreement to buy all the power generated by a 100-megawatt wind farm to be built near one of its data centers in Mayes County, Oklahoma, Google announced in a blog post Thursday.
It's Google's second investment of this type in the past year. Both were made by a subsidiary company, Google Energy, which is certified to buy and sell power on the U.S. wholesale market.
"These purchases represent long-term, meaningful actions to reduce our carbon footprint and power our operations with clean electricity," Google said.
The company also published a white paper Thursday that explains the complexities of trying to use renewable energy to run a data center. For regulatory and other reasons, Google can't take the power generated by the wind farms and apply it directly to its data centers.
"At our data centers, Google is a retail customer -- we have no way of taking power off the grid wholesale and applying it to our load," it says in the white paper. "We have to buy power just like you do: from our local regulated utility."
Instead, Google sells the power it agrees to purchase back to the grid at local, wholesale prices. The purchase agreements provide the financial incentive for the wind farms to get built, it said, and Google gets to collect Renewable Energy Credits for the wind power it sells. RECs are akin to carbon offsets, except Google says they are more effective because they represent renewable power that has actually been produced.
"Even if we can't legally or physically transfer the [wind] power to our facility, being in the same power market ensures we are contributing to greening the grid where we operate," the company said.
Both the wind farms are being built by NextEra Energy, in which Google has made an investment. It said the Oklahoma facility will be operational by late this year.
Google made its announcement at GigaOm's GreenNet conference in San Francisco. Greenpeace was also there, to step up its campaign against Internet companies that it says rely on power from coal-fired plants to run their data centers.
A new Greenpeace report, "How Green is Your Data?" criticizes Facebook, Google and Apple for building data centers in North Carolina, where it says "cheap and dirty coal-powered electricity is abundant."
"The IT industry points to cloud computing as the new, green model for our IT infrastructure needs, but few companies provide data that would allow us to objectively evaluate these claims," Greenpeace says.
Greenpeace argues that big Internet firms should locate their data centers where the local utility companies are producing renewable energy, in order to reduce their carbon footprint and encourage further investments in renewables.
It also credits Google for its efforts, however.
"Of the 10 brands graded, Akamai, a global content distribution network, earned top-of-the-class recognition for transparency; Yahoo had the strongest infrastructure siting policy; Google and IBM demonstrated the most comprehensive overall approach to reduce its carbon footprint to date," Greenpeace said.
Google, in its white paper, suggests running a data center on renewable energy is more complicated than Greenpeace implies.
"We know from Kirchoff's circuit laws that electricity generated in one spot cannot be directed to a specific user over the electricity grid," Google said. "Once you put electricity on the grid there is no actual way to say 'the energy from wind farm X is going to my data center Y.'"
