Google released a study (PDF) today concluding that using cloud-based email is more energy efficient than running email in-house. The company isn't the first to preach the green advantages of cloud computing, but Google stands to gain from successfully working the case as it looks to make Gmail converts out of shops running Microsoft Office and other rivals.
The underlying theory that cloud computing is more energy efficient than on-premises hosting is pretty sound, generally speaking: Cloud service providers have the advantage of economies (more users per server), as well as shared power and cooling resources. Additionally, their business model is based on providing services as efficiently as possible.
For the study, Google determined the average amount of energy necessary to run email in-house at a small business with 50 email users, a medium-size business with 500 users, and a large business with 10,000 users. The study assumed that the small and medium-sized businesses would require 2 servers (a primary and a backup), whereas the large company would require 12 (10 plus 2 backups).
All told, combining the costs of powering and cooling the servers along with the other IT infrastructure necessary to deliver email to a user's PC, Google determined that providing email to a single user at a small business uses 175 kWh (kilowatt hours) per year (70 kWh from the two 200W servers and 105 kWh from power, cooling, and the like). A user at a midsize business would use 28.4 kWh per year (16 kWh from operating two 400W servers and 12.4 kWh from cooling and such). Finally, the large-business user would burn through approximately 7.6 kWh per year (4.7 kWh from 12 450W servers and 3.1 kWh from the non-IT resources).
Tthese figures point to the energy-efficiency gains that can be reaped through higher scalability, increased users per server, and shared power and cooling. In that vein, Google assumed at PUE (power usage effectiveness) of 2.5 for the small business, 1.8 for the medium-size business, and 1.6 for the large business.
By comparison, Google claims that, thanks to its various feats of data center efficiency, it is able to provide Gmail at an annual energy-per-user rate of less than 2.2 kWh. Google attributes this to its highly efficient servers, its server-optimized software, and a PUE of 1.16.