In its ongoing quest to convince businesses and individuals to abandon the archaic practice of operating their own servers and shift their IT operations to the cloud, Google has frequently asserted that cloud computing is more cost efficient than servers run on-premises.

Now Google can argue that the cloud is more energy efficient, too. Citing its own research, supported by related findings from the Carbon Disclosure Project and from a consulting professor at Stanford, the company says that Gmail is almost 80 times more energy efficient than in-house email.

Google green engineering product manager David Jacobowitz explained in a blog post that Gmail's superior energy efficiency is due to the fact that cloud-based services come from optimized data centers that utilize their servers more fully than in-house systems. Small businesses, he says, seldom build systems that operate as efficiently.

Google's report notes that for a 50-person office, choosing Gmail instead of a locally hosted server "can mean an annual per-user power savings of up to 170 kWh and a carbon footprint reduction of up to 100 kg of CO2." The gains for larger organizations, the report said, are smaller--enterprises already benefit from economies of scale--but still appreciable.

At a commercial rate of $0.10 per kWh, that translates to a savings of $17 per employee annually. That makes the already low price of $50 per user per year for Google Apps for Business look even more competitive.

Google also ran the numbers for YouTube and found that the server power required to play a minute of YouTube video comes to about 0.0002 kWh of energy. "To put that in perspective, it takes about eight seconds for the human body to burn off that same amount," wrote Jacobowitz. "You’d have to watch YouTube for three straight days for our servers to consume the amount of energy required to manufacture, package, and ship a single DVD."

However, the cloud math for businesses may be more complicated than solving the email equation for a green variable. What's the cost of surrendering control and having valuable data guarded by a third party? That answer isn't obvious for every organization.

And the clear merits of cloud computing become muddier when "greenness" is defined not just by energy efficiency, but by whether the energy comes from a clean source, a consideration Greenpeace supports. The IT industry's "failure to commit to clean energy in the same way energy efficiency is embraced is driving demand for dirty energy, and is holding the sector back from being truly green," the environmental group said in a report in April.

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