Features

Not surprisingly, the most energy-efficient computer of all isn't a desktop, but a laptop. According to our tests, a notebook typically consumes one-quarter the power of the average desktop system, and its power-saving capabilities are likely to be more comprehensive. The price is no longer prohibitive - even business laptops are cost-competitive with desktops and, thanks to Turion X2 and Core 2 Duo, there's no need to sacrifice performance.

If you must have a desktop, buy sensibly. Look for energy-efficient processors (Core 2 Duo processor or the specially marked energy-efficient Athlon 64 and Athlon X2 CPUs), low-rated power supplies (between 250-300W) and passive or intelligent cooling systems (which alter the speed of fans according to the temperature of the system). You'll not only get a more energy-efficient system, but a quieter one too. If you need more power for video editing or games, a Core 2 Duo processor will provide maximum performance for less drain, and there are settings available to keep down your power consumption. Don't overclock, either - it can dramatically increase the power drain of your CPU.

Think smarter about your peripherals. Buy an all-in-one instead of a separate printer and scanner - you'll only have one power supply to feed, not two. And while replacing CRTs with TFTs makes sense (a 19in TFT consumes less than half the power of its CRT equivalent), bear in mind that a bigger screen consumes more power. That 120W 24in widescreen monster could push you back into CRT territory.

Determining which equipment is most energy efficient should become easier later this year with the introduction of the new Energy

ADVERTISEMENT

Star specification. According to Catriona McAllister, senior consultant for AEA Energy & Environment, the key point is that the new Energy Star label will be more demanding, covering power consumption on (idle) and off (standby) modes, and asking manufacturers to fit 80% efficient power supplies. Current PSUs, often provisioned for worst-case scenario power loads, are so inefficient that only as little as 20% to 70% of the energy consumed is actually utilised. McAllister calls this "a big step in the right direction", stating that "the new revision of the Energy Star specifications has been developed so that only 25% of the market (at time of definition) will be able to meet the requirements. This means that in 2007, the Energy Star label will provide a differentiator for consumers between products on the basis of energy efficiency."

Of course, she adds, it would help if power management was enabled on all PCs when delivered. Why is this not the norm? Partly because, as McAllister admits, "There are technical issues with power management, which need to be overcome through co-ordination between software and OS developers and hardware manufacturers to ensure all PCs successfully go to sleep and wake rapidly when required by the user." Interestingly, for instance, while Dell enables power management on all Optiplex desktops and all its notebooks, less than 15% of the Dimension desktops sold in fiscal 2005 shipped with power management fully enabled. Why? Dell claims a change to standby mode in Windows XP MCE required the end user to physically push the "sleep button to activate standby mode", so it couldn't pre-enable power management.

Carbon-free computing

For the ultimate green PC, energy efficiency is only the start: carbon-free computing is the hot topic. This works on the concept of planting trees to offset the energy used by your PC. It's an idea that's slowly gathering momentum. In October, VIA announced the C7-D: the first "carbon-free" CPU. For every one of the low-drain processors (20W at 1.8GHz) sold, VIA would plant four trees to offset its power consumption. To put this in perspective, had Intel done the same for the Pentium 4 each CPU would need 31 trees planted, according to VIA.