Green Hands USA: America Volunteers

If you're buying a new computer, and you want to make sure you choose the most energy-efficient model, there are three things you need to consider: power use when idle, during sleep mode, and when off. (Yes, even computers that are "off" continue to use power.)

How will you find this information? It's not exactly printed on the side of every computer, is it? Well, no worries. The UK energy-efficiency site sust-it.net has benchmarked dozens of computer models for you, and come up with a great list of desktop, laptop and all-in-one computers that lists their exact energy costs.

So who makes the most energy-efficient computers? It depends on which type of computer you want, but Apple ranked very highly on all three lists. The top four most energy-efficient desktop computers were all Mac Minis, as were two of the top four laptop computers. Apple also did well in the all-in-one category, with two iMac models in the top ten.

Unfortunately, not every Apple computer proved to be energy efficient. Apple also had several computers at the bottom of each list, proving that there can be a huge range of efficiency among models from the same brands.

How did other computer manufacturers fare? Asus makes four of the top ten energy-efficient desktop computers, as well as four of the top ten all-in-one computers. Dell has four of the top ten energy-efficient laptop models, including the two most efficient laptops. Dell and HP also had some of the least efficient laptops.

Give sust-it.net's full list a good review if you're in the market for a new computer. It will tell you not only which machines are the most efficient, but the estimated annual electricity cost for each model (in British pounds), as well as the estimated amount of greenhouse gases that energy will release. Let their research be your guide to a greener computer.