Kate's Comment

People keep going around and around in circles on the debate of whether you should replace servers and desktops sooner rather than later when you take into account the improvements in energy efficiency in recent years combined with the embedded energy cost of manufacture of computers. So, I decided to get out my calculator and made some interesting conclusions.

Materials, manufacture and distribution of an average PC currently in use today is is between 750 kilo Watt hours (kWh) for the most modern “green” PCs, and 1,300 kWh for machines of a few years go. You then have to add on about 300kWh for a LED screen (500kWh for a CRT screen). Even if we take the best case scenario we are still looking at a minimum of 1,000kWh for a desktop system, and laptops will only be a little less (most of the energy in PC manufacture goes into making the small, complex components such as chips).

An average PC made within the last few years, with its screen, uses about 100W when powered up and 3W when in hibernate mode. If we assume that the PC is on for 8 hours per day, 5 days per week, and is hibernating overnight we get 200kWh/year “on” usage and 20kWh/year standby usage.

So, a 3-4 year old PC probably used 1,200kWh to make and uses 220kWh/year to run, whereas a modern super-green PC might use 1,000kWh to make and burn 150kWh/year. To look at it financially, you will save about £7/year by switching to a super-green PC. Therefore it makes neither financial nor environmental sense to swap out old PCs before about 6 years. If you need to update the software, then switch to some sort of virtual desktop infrastructure instead and use the PCs as thin clients.

The same sums applied to servers on 24/7 are quite different though. An average £1,000 1U rack-mount server bought 3-4 years ago probably “cost” about 1,000-1,500kWh to make and uses 120W at moderate load, which over a year is 1,050kWh, or at least 1,500kWh when data centre cooling is taken into account. The latest equivalent “green” servers use as little as 80W, so swapping to energy efficient servers will save 400kWh/year in electricity and get you 2-4 times more performance.

With good use of virtualisation to consolidate existing applications onto a smaller number of machines (thus taking advantage of the performance improvements) it makes clear environmental and economic sense to replace machines after 2-3 years. Alternatively, if IT is not your core business activity then you could always consider outsourcing your server infrastructure to a carbon neutral IT host such as Memset of course.

As for the old servers, why not give them away to Africa via Computer Aid International, where our “outdated” hardware is much needed and will be put to good & efficient use (ie. it will only be on when they need it).

Addendum June 2009: There are some very cool technologies like Very PC’s Greenhive (a hybrid between PCs and thin client) which are changing the argument around replacing desktop PCs.

Thin client is also reaching maturity now that you can get a decent amount of bandwidth from ADSL and that Windows Server 2008 includes most of the functionality of Citrix at no extra charge. Thin client is definitely the future I think.