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How much power do (relatively new) computers consume while in sleep mode? By sleep mode, the computers' fans are turned off, producing no noise; and the LED on the power button blinks.

Do I need to be concerned about the power used in this state (keeping memory intact and the blinking of the LED)? Is it true that the electricity bills from leaving the computer in sleep mode overnight for a year amounts to a price greater than the cost of the computer?

Thanks.

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4 Answers

up vote 12 down vote accepted

I have a power/watt meter handy, so I thought I'd measure the family PC in various modes. It's an old 1.8 GHz AMD Sempron eMachine. This is just the box, and not the monitor or any other peripherals.

  • Off (just plugged in): 3.0 W
  • Stand-by (everything off, LED flashing): 4.5 W
  • On, but idle: 75 W

Like all device that don't use a hard, physical switch (TVs, DVRs, etc.), you will get some power draw on the order of 1-to-5 watts per device. The costs of these "ghost loads" over a year depends entirely on how many you have and what your kW-hr billing rate is.

Being a power miser, I use a power strip on the family PC, attach everything to it, and then flip the main switch off when not in use.

EDIT: I did the math for this machine while "off". My rate is 8-cents per kWh, so:

3W * (1kW / 1000W) * (24h * 365) * $0.08/kWh = $2.10

This is an absolute lower bound on the cost of having the machine plugged in for a year. With typical use it will be much more.

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You're eventually going to have to replace the battery that is used to power things like the internal clock and other similar things, but the cost of that is not going to be anything near what that 3.0W costs you. –  Kevin M Jul 1 '09 at 16:57
    
+1 for going the extra mile! Especially for a dubious initial question –  Izzy Jul 1 '09 at 16:57
    
+1 as well -- nice answer .. informative! –  tomjedrz Jul 1 '09 at 17:30
    
@Kevin - CMOS batteries cost $4 at the time of this writing, and they will probably last around 5-7 years, so given the lowest cost number above you'd pay off the cost of the the battery in 2-3 years, w/shipping. :-) –  J. Polfer Jul 1 '09 at 17:44
    
I have heard, though, that hard drives can get damaged by daily power cycling. I have nothing to substantiate it though, so it's likely an urban legend. –  J. Polfer Jul 1 '09 at 17:45
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If you're really concerned about the consumption either power down or hibernate the machine and then unplug it. I personally just hibernate and accept the few milliwatts the machine draws in that state (because Wake-On-LAN is active). Sleep mode allows the machine to come back up quicker but uses more power and runs the risk of losing the current state, and possibly damaging the file system due to improperly closed files, if the power drops.

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<joke>I suspect that rumor was started by the folks who make the Kill A Watt </joke>

These devices cost around USD $25.00, and can be used for any devices which use a Type-A or Type-B power connectors (the American 2 or 3-prong plugs).

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I wish those were around when I bought my $300 Brand Power Meter ten years ago. Even so, I think the knowledge gained by the meter has paid for itself several times over in that time, so it was money well spent. –  Geoff Fritz Jul 1 '09 at 19:03
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If you don't want to use ANY power but still have the computer at a somewhat-ready state, I always put it into hibernation. Of course you'll need a couple gig's of HDD space to enable hibernation. Just a thought.

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