Turn On?

People often stop me in the street and say “Hey, Pete. Should I leave my computer on all the time, or turn it off when I’m not using it?”

Well, here are your answers. Once and for all. Real facts coming your way…

Q. *Won’t leaving my computer on all the time consume lots of power?*
A. Depends. If you left it working flat out on mathematical calculations, then yes – over £100 per year. If you leave it doing nothing with the monitor switched off, then about £15 per year. If you put it into “hibernate” mode, then it will consume sufficiently little power to be insignificant.

Q. *Doesn’t turning it on and off wear out the components?*
A. Yes, to an extent. However, you’d have to turn it on and off about a dozen times a day, every day to see any difference. The additional stress caused by turning it on and off twice per day isn’t significant enough to be worth considering as a factor.

Q. *Does leaving it on all the time wear out the components?*
A. Again, if you leave it on all the time when you aren’t using it, then you will shorten the life of the components, but really not by much at all. Very few home computers actually die because the components wear out – they are normally just abandoned because they become laden with spyware, junk or trojans, or they are replaced for a better model. Don’t let component life worry you.

Q. *So give me a good argument against leaving it on all the time.*
A. As long as you turn off the monitor to conserve power, the only argument I can think of is that while the computer is turned off, it can’t be attacked by miscreants. But then, as long as you’ve got a decent firewall, you shouldn’t really let that worry you.

Q. *In conclusion?*
A. Really, you can do what you like. As long as you aren’t bothered about £20 per year, there are no convincing arguments one way or the other. If you find yourself turning the computer on more than twice per day, then it may be worth leaving it on. Don’t leave the monitor on – that can waste a lot of electricity. If you want to save more energy, use hibernate mode.

Q. *Where do the numbers come from?*
A. A computer running at full pelt is about 200 watts, or 0.2 kilowatts. There are 8766 hours in the year. 0.2 * 8766 = 1753.2 kilowatt-hours. At 6p per kWh, we get £105.20 per year. When idling with the monitor switched off, the computer consumes about 30 watts, which is about 263 kWh in a year. This comes out at £15.78. These are only rough estimates, based upon an average computer and an average electricity tariff.

Q. *Thank you. I shall not take these figures as gospel. I shall just use them to get a rough idea.*
A. That’s the spirit.

**UPDATE:** As Lyle rightly points out in the comments, computers don’t like power cuts. Shame on me for omitting to mention this. If you live in an area with an unreliable power supply, then you should turn your computer off when you aren’t using it (though I expect that if you are in this situation then you have already bought a laptop). Also, if there is a storm brewing and you think that the power may go out, turn your computer off, switch it off at the wall, unplug it from the mains, and put the plug on a non-conductive surface (like plasticene or velvet).

**2008 UPDATE:** The numbers, of course, are prone to change. Three years later, electricity costs twice as much, and I found that my current computer draws about 70 W when idle. £15 becomes £50.

*Originally posted here*

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