Unplug phones to save power

One other thing that caught my eye recently: a report from a mobile industry task force led by Nokia that extolls the virtues of unplugging your phone after it’s charged. The report claims that if 10 percent of mobile phone owners would unplug their phones when done charging…

it would reduce energy consumption by an amount equivalent to that used by 60,000 European homes per year.

Something about that seemed a little strange to me, so I did an experiment and some math. There are now 2 billion mobile phones used worldwide. Using a device called a Kill-A-Watt, I measured the power consumption of two different phones I had handy: a Samsung (3 watts charging) and a Treo 650 (4 watts charging). Both, however rounded off to 0 watts once the batteries were topped off.

Older power “bricks” feel like they have a hunk of solid iron inside because, well, they do. A transformer takes continuous current through its primary coil, quite independent from the device attached, if any. Newer power bricks–the lighter ones that feel almost hollow–use switching power supplies that are far more efficient.

Half a watt, say for an extra 8 hours a day, times (10% of 2 billion = ) 200 million phones is 800 megawatt-hours. Over a year, that’s 292 gigawatt-hours. Those billions add up fast.

To estimate how much power homes would use, let’s pick an easy figure of continuous average of 1kw. In a year that’s 24 x 365 = 8.75 megawatt-hours, and for 60,000 homes, it would be 525 gigawatt-hours.

So the numbers are at least in a similar ballpark. But statistics are tricky. To put it in perspective, my Dremel tool (with a transformer) consumes about six times as much power when fully charged. So if only 10% of mobile users would unplug their Dremels, it would conserve the power of 360,000 homes. Turning off one light for an extra hour a day: 1.5 million homes. If you really want to save energy, start with the bigger things. (But that doesn’t seem like a message likely to come from a group led by a handset maker. :-)

Is my math right? Let me know in the comments.

P.S. Not to be totally cynical, the task force is doing good things, including getting manufacturers to use less toxic heavy metals and nasty phthalates. -n

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