It also helps that it is a technology-driven company willing to invest in energy-saving ideas. It brought its first solar farm online in December, generating 650 kilowatts of power, and it plans to install Bloom fuel cells later this year that will provide up to 6 megawatts of power.
The software, hardware, operations and finance teams at eBay are working together on the project, Nelson said. In one experiment, its software developers adjusted the memory utilization for a pool of servers, allowing it to eliminate 400 machines and save a megawatt of power, he said.
PUE was controversial when it was introduced by the Green Grid Forum six years ago, Nelson said, but it has since been adopted widely.
Like PUE, the "miles per gallon" data isn't necessarily useful in and of itself, but it could give companies a benchmark to measure progress moving forward.
"We averaged 46,000 transactions per kilowatt hour last year. Was that good? We don't know, we have nothing to baseline it against," Nelson said.
This year, eBay -- and everyone else -- will be able to see how it's doing.