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On or Off? How Much Energy Does it Cost?

Cheryl from OH writes:

A friend of mine told me she turns her monitor off, but leaves her tower run at night. Is there an advantage to this?

The practice of leaving a computer on, but turning the monitor off is mostly used in the office/corporate environment, because many updates/system upgrades are done by IT departments later on at night when the PCs are on, but very few (if anyone) is in the office. While Windows does automatically schedule some system tasks (like disk defragmenter) to run late at night, it’s not the best idea to leave your tower on all the time.

turning off pc=time+money

Why not? If companies do it, then it can’t be too bad, right?

1.) Money. If your PC consumes 150 watts of power while it’s on – ¬†and let’s say you use it for a total of 8 hours during the day – then the remaining 16 hours in the day uses 2400 watts of extra power. Over the course of a year that’s 876,000 watts of power. Let’s say your average cost per kilowatt-hour for electricity is 14.9 cents. That would total $130.52 over the course of a year of wasted money.

2.) Wear and tear on the computer. A computer contains many different kinds of components, some which have almost infinite lifespans, and others which have limited lifespans. A hard drive, for example, spins and has only an average number of hours of spinning before the motor normally fails.

This MTBF (mean time between failure) is usually quite long, but the more hours the hard drive is up and spinning the less hours it has left. Your computer also has ball bearing fans that cool the various system components (which also have motors) and the more air they move the more dust they collect. All of these considerations lower the total time the computer is likely to run for and increase the risk of failure.

Are these reasons enough to turn off your PC at night? It depends on what you value. If you’re someone who prefers the instant on response of a PC which is always ready, then it may be worth the $130 a year plus extra wear-and-tear. If you don’t mind waiting a little for the computer to boot up, then you may want to turn it off every night when you’re done using it.

P.S. A good middle ground is the hibernate function, which writes everything in your computer to the hard drive and turns off your computer. Once you power it back on, Windows restarts right where you were. You gain the ability to go right back to what you were doing without leaving the PC on all night. The downside is it’ll take Windows time to boot back up and load back to where you were – about a minute or two.