# How much electricity is used?

In each of the following cases, please label the electricity used as (A) very little (less than 1 dollar a month), (B) moderate (between 1 and 5 dollars a month), (C) high (between 5 and 10 dollars a month), or use your own words.

1. Leave my computer in standby mode.
2. Leave my computer in hibernate mode.
3. Turn off my computer but the cord remains plugged.
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What are electricity prices in your area? – AndrejaKo Jan 6 '11 at 23:37
Why do you make this sound like a homework problem? xD – Shinrai Jan 6 '11 at 23:40
@Andreja. About 11.35 cents per KWh. @Shinrai. Being a teacher before, I tend to write a question like a homework. But this is of course not a homework. – TCL Jan 6 '11 at 23:59
Damn! I was just about to measure power consumption and then I remembered that I don't have a working desktop computer... – AndrejaKo Jan 7 '11 at 2:02

Since I don't have a good computer to use for direct measurement, I'll use Wikipeda and compreviews.about.com as my sources for power consumption calculations.

First, in my area a "month" is considered to be a period of 30 days, so I'm going to use that for calculations. So 30*24=720 is the number of hours in a month. Next step is to determine power consumption of a device in watts and multiply.

So they say that on PC which is Energy Star certified (and I don't remember when I've seen one which isn't), power supply can't use more than 2 W when in stand-by and more than 4 W when in sleep. I'll take 4 W for calculation purposes.

So 4 W * 720 h = 2880 Wh = 2.88 kWh. We multiply that by the energy price, so we get:

2.88 kWh * 0.1135 \$/kWh = 0.32688 \$.

That means that all answers are A), since hibernate and power-off can't spend more than sleep.

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If the cord is unplugged then it cant be pulling any power. Hibernate also doesn't require any power since the machine saves your state to disk.

Standby requires power to keep data in memory, although it is the fastest state saving option due to memory access tims vs disk I/O times.

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I made a mistake. I meant "remains plugged" not "unplugged". – TCL Jan 6 '11 at 23:15
If you leave the cord plugged in, it will still use some power. Not as much as standby but enough to power the motherboard LEDs =) – John T Jan 6 '11 at 23:21
According to this article Hibernate uses power, or at least the motherboard does, because the power cord is plugged in, If you disconnect the power cord after you hibernate, then it is 0...terranovum.com/projects/energystar/standby_v_hiber.html – Moab Jan 6 '11 at 23:46
Hibernate mode itself does not require power. You can unplug the machine from the wall after entering hibernate and plug it in elsewhere to return it's state. Most motherboards nowadays will use power for the LEDs whether the machine is on or not. intel.com/support/motherboards/desktop/sb/img/led300.jpg – John T Jan 6 '11 at 23:54
It also uses a small amount of power to power things like the network card to support thinks like Wake On LAN if it is enabled on the motherboard. – Scott Chamberlain Sep 4 '13 at 14:07