Power Consumption for Our Two PC's Before and After Conservation Measures

The table below gives the details for power saving on our two PC's.

The total saving is a rather astonishing 1780 KWH per year.  This results in a saving of $178 in electricity costs and nearly 3600 lbs of CO2 emissions.

The current operating mode is as follows:

  1. During the day, we hibernate the computer when not in use, but do not turn peripherals.  I have the PC front panel on/off switch set to hibernate, so when I am not going to use it for a while, I just press the switch.  You can also set the PC to hibernate after some number of minutes of inactivity, but I find that this is not reliable on my PC.   When I want to use the PC again, I press the front panel switch, and the PC comes back from Hibernate quickly.
    The savings associated with this is 695 KWH per year for the two computers.
  2. For the night time shutdown, I put the PC's into hibernate, and power down all peripherals. 
    The peripherals for each PC are on a power strip, so this is just the flick of one switch. 
    We have a new gadget that I plan to try shortly that will automatically turn off the peripherals whenever the PC goes into hibernate.  This will allow some additional savings during the day, and save ALL THE WORK of flipping one switch at night :)

I don't know of any other way to save this much electricity so easily.

One of the key things to realize is that the PC peripherals (printers, scanner, speakers, router, ...) use  quite a bit of power.  As you can see from the table below, our peripherals use more power than the PC itself.   This means that its not enough to just set your PC to go into standby or hibernate -- this still leaves all your peripherals sucking power.

Table showing power consumption in the various modes as measured with a Kill-A-Watt meter:

Item Downstairs Office Upstairs Office
  On Steady Hibernate Off Mode On Steady Hibernate Off Mode
PC 74 1 0 90 0 0
Printer 11 11 0 7 7 0
Router + 21 21 0      
Scanner 10 10 0      
LCD Monitors 52 2 0 26 1 0
Speakers 4 4 0      
Phone + Intercom 2 2 0      
Total (watts) 174 51 0 123 8 0
Measured Totals 174 54 0 100 to 128 10 0


"On Steady" Mode means the steady state power consumption after all initial startups are done -- for printer it is NOT during printing

"Hibernate" Mode means that PC is placed in hibernate, and all other things are whatever they go into when PC hibernates (e.g. LCD's consumption drops a lot)

"Off" Mode means zero consumption (power strip turned off)

1 -- the LCD monitors use about 26 watts when displaying a picture, but go down less than a watt when the computer goes into hibernate.

Savings Calculation

Power Strip Saving  --

Assume 10 hrs per night with no power use --

Savings = (10 hr/night)(365nights/yr) (Steady On Power)/1000  =  1084 KWH per year

 Hibernate Saving --

 Assume 8 hrs per day of hibernate power use --

Savings = (8hr/day)(365 days/yr) (Steady Power -  Hibernate Power)/.1000 = 695 KWH per year

Total Savings = 1084 + 695 = 1779 KWH per year !!!!


Gary 3/31/07, updated/clarified Nov 7, 2007