How Much Does It Cost To Run Your PC?

Do you know how much it costs to run your PC each month? Until recently, I didn’t. In the past, I had speculated that running my PC 24/7 may cost about 10 dollars per month. However, with increasing fuel / electricity prices, my new estimation may surprise you.

Testing Strategy

Using simple readily available equipment that some of you may already own, I was able to reasonably measure the actual power consumption during run-time. I used a standard APC battery backup-unit and the ‘Power Chute’ utility that it came with. Other UPS (uninterruptable power supply) units may also have this capability.

Please note that I have manually modified the image below by enclosing in red the power usage in order to make it easier to identify. This measurement is an estimation of the average load on the battery backup unit itself due to the devices plugged into the non-interruptible power outlets.

Pic

APC Power Chute Utility 1

Note: An alternate method would be to locate the manufacturer’s specifications for all of your components and add up the theoretical power consumption values (watts) and perform the following math using those figures. However, that probably won’t yield a good average because your PC probably spends most of its time in power savings mode with many of the peripherals either turned off or in a low power state.

The Test

Using the configuration shown below, I was able to determine that my PC consumes approximately 196-210 watts while idling, 240 watts while running a Sisoft Sandra CPU test, 246 watts while playing Unreal Tournament 2004 with a resolution of 800 x 600 with 32-Bit color, and 256 watts with a resolution of 1920 x 1200 / 32-bit color. In both cases all possible graphical effects were enabled.

The above UT2004 figures correspond to playing the game through the Geforce 6800GT. None of these figures include the power consumption for the monitors, Ethernet switch, USB hub, web cam or other USB devices since that are plugged into alternate UPS for load distribution reasons.

However, by moving power plugs between both UPS units, it can be shown that the 2405FPW draws 50 watts, while the 2407FPW draws 72 watts. In total, all three monitors and external peripherals draw about 320 watts. This does not include two external Maxtor One-Touch drives which draw about 30 watts each. The complete test configuration is shown below:

Computer System Test Configuration

  • PSU: 500 Watt
  • Motherboard: Asus A8N-SLI-Premium
  • CPU: Athlon X2 4400+ (2 x 1MB cache)
  • RAM: 2 GB OCZ
  • Video Card 1: Geforce 6800 GT, 256 MB
  • Video Card 2: Geforce 7300 GT, 256MB
  • Hard drives: 3 SATA: 250, 300, 300 GB
  • Sound Card: Creative X-Fi
  • DVD RW(s): Two, various brands
  • Floppy: Existing
  • USB Hub / Devices: Web cam, USB dongles etc
  • Displays: Three 24″ Dell 2405/2407 FPW
  • External Hard Drives: Two, Maxtor One-Touch – Not Included

So, if we add everything up and assume that most of the PC’s time is idling (since web browsing and email are not very computationally intensive) then we have the following total:

Average Power Consumption

Device
Power Consumption

Computer System
210 watts

Displays and External Devices
320 watts

Total

530 watts!

Power Consumption Under Reasonable Load

Device
Power Consumption

Computer System
256 watts

Displays and External Devices
320 watts

Optional External Hard Drives
60 watts

Total

636 watts!

Calculation

If the PC is running 24/7, then the number of runtime hours, assuming 30 day months, can be computer as:

(24 hours per day) * 30 days = 720 hours

Given the cost of electricity to be 12 cents per Kilo-Watt hour, the cost to run the PC 24/7 under the Average Power Consumption is:

(0.530 KW * 720 hours * 12 cents per KW/h) = 4579.2 cents = $45.79 / month!

The cost to run the PC 24/7 under the Reasonable Load Power Consumption is:

(0.636 KW * 720 hours * 12 cents per KW/h) = 5495 cents = $54.95 / month!

Conclusion

It is quite expensive to run a reasonably high-end PC 24/7. Unfortunately, I rely on the services that my PC provides when I am not in front of it and therefore cannot shut it off while away from keyboard. However, I could shut it off while sleeping, which would save $15.27 / month in the Average Power Consumption state, and $18.32 / month in reasonably loaded state.

These savings assume 8 hours of sleep and that your PC is relatively idle while not actively being used. There are of course some exceptions depending on your required background services and or running applications.

In conclusion, I am surprised at the relatively low power consumption levels for the PC. I was under the premise that the CPU would draw 90 watts or so on its own, plus 20 or so for each stick of RAM (4 sticks, 80 watts), 30 watts per hard disk (90 watts total), and so forth. However, given these results, perhaps Windows XP’s power management algorithms are doing a better job saving power than previously thought possible. If this is the case, than bravo to Microsoft, because if all devices were under full load all of the time, I would expect my electric bill to be considerably higher.

PS: Here’s a link to a PSU Calculator which can estimate your power needs based on what peripherals are included – very hand! Don’t forget to hit “Calculate” when finished.

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