Google has finally opened up about its datacentre technology and has claimed that its server operations are "the most efficient in the world."

Up until now, the search engine giant has remarkable secretive about what goes on inside its datacentres, but the claim was made in a blog post from Urs Hölzle, its senior vice president of operations, when it published the results from internal studies.

While some of what it does, like designing its own servers, isn't practical for most businesses, other tricks could be replicated by other companies, albeit for an upfront capital cost.

Its announcement coincides with a speech about energy given by Google CEO Eric Schmidt, in which he called for the use of alternative energy sources such as drilling for geothermal energy, as well as utilising solar and wind, in order to reduce America's oil dependency.

Google uses a metric called PUE, or Power Usage Effectiveness, to measure its datacentre efficiency. It gives a ratio of the total power consumed by a datacentre to the power consumed by the IT equipment used in the facility. For example, a PUE of 2.0 indicates that for every watt that directly powers the IT equipment, an additional watt is used to cool and distribute power to that IT equipment.

In a report to the US Congress in 2006, the Environmental Protection Agency estimated that the typical enterprise datacentre had a PUE of 2.0 or higher. It also forecast that by 2011, datacentres employing "state of the art" techniques such as liquid cooling could reduce their PUEs to 1.2.

Google said Wednesday that it has achieved that PUE as the average across all of its datacentres, and that one of them operates with a PUE of 1.13. "Today we are operating what we believe to be the world's most efficient datacentres," Hölzle wrote.

That's no small claim given that many of its competitors are also experimenting with datacentre designs to improve efficiency. Microsoft and HP has been packing servers into shipping containers, creating a closed environment that allows it to manage cooling more efficiently. Microsoft said recently it had achieved a PUE of 1.3 in one of these containers. They are not widely in use yet, but Microsoft plans to put more than 200 of them at a new datacentre in Chicago.

Google starts its energy push with designing better servers, which typically waste a third of the energy they consume before any of it reaches the components. The company uses highly efficient power supplies for the servers and efficient voltage regulators on the motherboards. It said it also strips out components that it doesn't need, like graphics chips, and designs computers and server racks to use as little fan power as possible.

The company says it saves $30 (£17) and 500kWh per year for each server, and puts 300kg less carbon dioxide into the atmosphere.

For its datacentres it focused on cooling, which can account for up to 70 percent of the overhead in energy use. It uses water evaporation to minimise the use of its chiller equipment, which is basically a large air conditioner for the datacentre. It showed a photograph of a large cooling tower in Oregon that it uses for water evaporation.