clipped from: www.codinghorror.com Between my server and my Windows Media Center home theater PC, I have at least two PCs on all the time at home. Have you ever wondered how much it's costing you to leave a computer on 24 hours a day, 7 days a week?
The first thing you need to know is how much power your computer draws. The best way is to measure the actual power consumption. You'll need a $30 device like the Kill-a-Watt or Seasonic PowerAngel to do this accurately. Once you get one, you'll inevitably go through a phase where you run around your home, measuring the power draw of everything you can plug into a wall socket. For example, I learned this weekend that our 42" plasma television draws between 90 watts (totally black screen) and 270 watts (totally white screen). Based on a little ad-hoc channel surfing with an eye on the Kill-a-Watt's LCD display, the average appears to be around 150 watts for a typical television show or movie.
But I digress. Once you've measured the power draw in watts (or guesstimated the power draw), you'll need to convert that to kilowatt-hours. Here's the kilowatt-hour calculation for my server, which draws ~160 watts:
160 watts * (8,760 hours per year) / 1000 = 1401.6 kilowatt-hours
The other thing you'll need to know is how much you're paying for power in your area. Power here in California is rather expensive and calculated using a byzantine rate structure. According to this recent Mercury News article, the household average for our area is 14.28 cents per kilowatt-hour.
1401.6 kilowatt-hours * 14.28 cents / 100 = $200.15
So leaving my server on is costing me $200 / year, or $16.68 per month. My home theater PC is a bit more frugal at 65 watts. Using the same formulas, that costs me $81 / year or $6.75 per month.
So, how can you reduce the power draw of the PCs you leave on 24/7?