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On or Off? How Much Energy Does it Cost?

Friday, May 25th, 2012 by | Filed Under: System Tune-Up Help

Cheryl from OH writes:


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.


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8 Responses to “On or Off? How Much Energy Does it Cost?”

  1. Harold Robinson says:

    The Nextar GPS I just bought from Worldstart will not work. Tried to contact http://WWW.Nextar but they are no longe in business. Went to ask nextar tech, they wanted 24 to 40 dollars to answer question.
    Problem: Charged battery, when i turn it on, goes to first screen, (Navigator, Music, Photos, Setup). When I touch anything on screen, it cuts off. Turn off with switch on back, comes back on, but goes off when I touch screen.
    It will stay on as long as I don’t touch screen.
    I tried wirh it connected to car, computer, and to nothing. Does the same.
    Can you tell me what the problem is and how to fix it or do I need to return it to Worldstart?
    Harold Robinson

  2. ru says:

    …you mean 150 watts PER HOUR, right?

  3. robertpri says:

    I agree with the tip. Hibernate is best if you want to resume where you left off. However, two things: with the rapidly increasing number of laptops, I would doubt if they consume 150 watts/hour. My high end Asus uses 80 at max. And towers would be a lot higher than 150, so perhaps the tip is using a sort of average.

    The second issue is one that my company has debated for years with no solution. Does keeping a motorized device [hard drives, fans, etc] running full time last longer than turning it off every day? And then endure the high mechanical demand of restarting and coming to speed?

    We found that it works both ways. We have thousands of motored devices, not just computers, and found some will last longer if allowed to run 24/7. Unfortunately, the tests were not conclusive. We never did get an answer.

    [as a side note, I mentioned this to my wife who insists on running our room fans 24/7, only switching to low at night. She has proven to me they last longer]

    • K.Vee.Shanker. says:

      Hi Robertpri,

      I’m not sure how your wife has proven the extended longevity of fans through the non-stop operation. Any such theory needs extensive scientific study before conclusion. Additionally, what is the saving after power consumption? Until then, I’ll go by the proven idea that any mechanical device is subject to wear and tear with use. Longer the use, more the wear. It even applies to electronic devices, which may be just passive displays. The other extreme is the disuse. Business/critical situations do go over economy for other important considerations. They are not to be generalized with normal uses.

  4. robertpri says:

    My wife bought the fans for several rooms here in hot Stockton for over 35 years. Although not a scientific test, the ones that were shut down every night did not last as long. After a few seasons, those would not start again come summer. The ones she ran 24/7 would last several seasons. They were only switched on and off once a year. I have an ohmmeter and verified the cost at less than a dollar a month. Saving the fans for additional years saved the cost of buying new ones too soon.

    And I would challenge the notion that switching a device off and on every day is less wear on mechanical devices. Some yes, some no.

    This has been debated for years, and I have never found conclusive proof either way. That said, I’m retired from Trans World Airlines and they spent enormous time and effort studying this dilemma. We had thousands of mechanical devices around the world. This began when we left hanger lights on 24/7 and they lasted longer. This was confirmed by American Airlines and Pan American Airlines who followed our maintenance plan. Of course, this was due to heat, getting hotter and then colder caused the lights to fail early.

    The concept was then spread to hundreds of mechanical devices throughout the company world wide. Airlines do stick together, at least in those days. We exchanged maintenance records with the other airlines. After doing this for many years with thousands of devices, there was no conclusive proof either way.

    It seemed to vary with the device. So, some we left on 24/7, and some we turned off every day.

    Hard drives used to be have an MTBF of 100,000 hours. Not exactly a concern for any of us.

  5. robertpri says:

    I should have mentioned that global airlines have reliability teams that do nothing but try to improve the longevity of everything from copy machines to 53,000 #fn Pratt & Whitney engines. That is all these people
    did. When you have thousands of devices, every dollar counts.

    I was on various aircraft Reliability Teams but had years of interface with the other teams. The Office Teams learned that the computers in
    Reservations, Cargo, Maintenance, and terminal counters that ran 24/7 lasted just as long, and some times longer, than office machines that were turned off every night. But some didn’t.

    After detailed studies by three major airlines, it was not conclusive
    either way. So, the issue became time and wasted energy.

    As noted, I use hibernation every night and have for some time. I like to resume where I left off the night before, and save the energy.

    But it’s simply not a proven fact that switching off an electrically driven motor device every day will positively result in longer life.

    It might, or it might not. It’s been debated for years.

    • K.Vee.Shanker. says:

      Hi Robertpri,

      It is very nice of you to have shared so much with us, especially about detailed studies. As regards to fans(old models) at homes, I’ve seen fans functioning for ages that were switched off more than once a day. May be, it depends on design and quality too.Probably, it is a bad idea to switch on & off without complete cool off for the motor/gear. I’m not sure either.As you say, it is difficult to generalize.

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