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I'm asking this here because this is primarily a huge office scenario and administrators will more likely have the answer I'm looking for.

Employees' desktop computers can be either left turned on for the whole night or switched off in the evening and turned back on in the morning. The latter will surely save energy. In the same time turning on and off is very harmful for the equipment - hardware often breaks specifically when turned on.

Both energy and hardware replacements cost money. With energy it's quite obvious - you pay every month according to what your power meter shows. With hardware replacements it's worse - you need qualified stuff to quickly diagnose the problems and once something breaks the affected employee will have to wait for some time while his computer is fixed/replaced and the data is recovered.

So the company has to choose between saving money on energy and saving money on computer maintaince and lost hours. Such decisions must be well though.

Is there any detailed study of how turning computers off each evening affects their lifetime and what losses are induced by it?

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Ford Motor Company is about to find out. –  kmarsh Apr 7 '10 at 12:51
"Wear induced by turning computers off in the evening" does not exist. Turning computers off at night actually decreases wear. On the other hand, the savings are real: for old-fashioned desktop PCs, your company may save ~$3-8 per month per desktop, depending on specific PC models and power costs in your area. One issue that actually is worth considering: you will need to have a system in place to "wake up" computers during normally idle periods for maintenance (especially OS updates). –  Skyhawk Jun 23 '10 at 18:42
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6 Answers

up vote 8 down vote accepted

I work for a large state government where we recently began implementing power management. According to our calculations based on metering a sample population shutting off PCs during idle periods saves about $35/PC per year for a mainstream business desktop with LCD monitor. Your mileage will vary, so do some testing yourself.

Laptops are generally provide for less savings, CRT monitors and workstation class devices increase savings.

We looked into the issue of hardware failure at great length, and based on research, testing, and a production implementation that's about 6 months old, I can find no evidence supporting the assertion that turning a computer on and off "wears out" anything or causes other hardware related issues. We've observed no statistically significant increase in hardware failure. (If anything, it has gone down slightly due to refresh of older equipment.)

You will find other issues, such as:

  • Annoyed end-users
  • Older PCs that don't like to resume properly
  • Misbehaving applications

These issues don't have magic bullet fixes. You need to communicate with end users, test your applications and test your older hardware.

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We went through a similar process last year. Most research we found didn't show a large difference in the life of the computer. Considering most computers are replaced after 4-5 years, you might as well save the $200 over the life of the computer. Also, we noticed the largest differences in power consumption by replacing old technologies (like CRTs) and simple 'fixes' like enabling stand-by after an hour, or turning off the monitor after 30 minutes. More reading: michaelbluejay.com/electricity/computers.html –  Chris S Jun 23 '10 at 18:45
+1 for "Annoyed end-users". We've tried power management, nightly shutdowns and scheduled morning BIOS power-ons. People still get upset (and I don't know why). We can't win. :) –  jscott Jun 23 '10 at 18:48
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First, if this is a "huge office scenario", you will hopefully have warranty contracts that covers most of the lifetime of the machines. In that case, if it breaks, it's the vendors job to repair it and you can just reap in the energy savings.

Beside that: While I would agree that there is a somewhat increased possibility that hardware will die during a power cycle, I consider this to be a problem of (really) old hardware and I can't see how one cycle every working day over a course of three to five years would cause a problem except on very crappy hardware that might die anyway whenever you look at it the wrong way.

One major issue remains, which decides the whole game in my opinion, and this is the harddisk. Desktop drives are not designed to run 24x7 and I personally experienced a significant amount of drive failures of non-raid-type drives used in 24x7 server scenarios.

So, in the end: Turn the machines off and save the energy. There is nothing else to gain.

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I seriously doubt warranty will cover lost hours. –  sharptooth Apr 14 '10 at 8:38
Again, you are talking about a "huge office scenario". For me, this means having replacement machines available, automatic deployment etc. etc, with maybe a 30min time for replacing a dead machine. And as I said, keeping systems running actually increases the chance of a hardware failure. So, in my book there are no two choices between saving energy and saving money on maintenance and lost hours, because you get both by turning machines off. –  SvW Apr 14 '10 at 9:59
If you're in a "huge" office and have dedicated IT staff, a PC failure should not be an event that takes hours to recover from. You should be seeing 3-5% failure rates already, and have procedures for dealing with them. –  duffbeer703 Apr 30 '10 at 17:23
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Not switching PCs off may cause overheat which decrease hardware lifetime.

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True, but if a computer has problems with heat it will incur enough damage even during a normal 9-hours day. I agree that 9-by-5 is much less then 24-by-7, but still I'm asking about normal functioning. +1 anyway - an important factor to consider. –  sharptooth Apr 7 '10 at 7:46
Actually a lot of desktop hardware is only rated for 9 hour cycles, not for 24/7... For that you are expected to buy "server" hardware. –  pehrs Apr 7 '10 at 8:08
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Sorry but I didn't get you where you say "hardware often breaks specifically when turned on." Does turning computers off and on damage them ?

Further, I would suggest having the machines to be put into suspend mode, if it is not possible to switch them off completely, so that at least some power is saved :)

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Yes, turning any piece of electronics off and then on several times usually causes more damage to it than just running it for several minutes. –  sharptooth Apr 7 '10 at 8:15
Hmm...interesting, didn't ever think of that :) BTW, A google search took me here...maybe something in this maybe useful for you. federalelectronicschallenge.net/resources/docs/oandm.pdf –  Knight Samar Apr 7 '10 at 20:30
No, turning electronics on and off does not damage the hardware. (At least not in the context of energy management.... abusive behavior like rocking the power switch back and forth obviously isn't a good idea.) –  duffbeer703 Apr 30 '10 at 17:17
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How much does it cost in power to run the PCs 24/7? This is a question most companies can't answer off the bat. However, it should be considered that of 168 hours in a week, each PC will be used around 40 hours, or however long your working week is (at most, there's still lunch break and not everybody does all work on the PC all the time). This means you quadruple energy consumption by not switching them off.

My office desktop draws 250 W, so I use 1 kWh every four hours, or 42 kWh per week, if I left it running all the time. If you pay $0,15 per kWh, this means more than $300 a year, of which $225 are just waste. At that rate, the damage done by a power cycle every weekday would have to decrease the MTBF quite drastically to get economically meaningful.

I switch my PCs and laptops off whenever I know I won't use them for the next 30-60 minutes. I have used them for many years that way. In fact, I have never even heard of a PC breaking by switching it on and off.

In working as an energy consultant for businesses, I've seen this theme pop up over and over. Not just the PCs, your whole building is only used 25% of the week. The amount of energy that's used outside those hours, for all kinds of things, is astonishing, to say the least.

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I wish I had detailed data, especially the type of numbers you want.

You might simply need to do A/B testing to see which is better.

However, I would say that the harm of turning stuff on-and-off is kind of hypothetical sounding to me:

The latter will surely save energy. In the same time turning on and off is very harmful for the equipment - hardware often breaks specifically when turned on.

First, what is the lifetime of a PC? Lets say it is 5 years. Turning it off and on again once a day really is not a lot. I remember, in my childhood, we turned off Apple's, IBM PC's and Atari class systems a dozen times a day, for years. Computers have only gotten more reliable since then.

Second, I doubt a higher failure rate can be can be uniquely associated to the daily-power down. Even if you leave your computer on all the time, you still have to reboot for system updates. In my experience, that is the source of most of my boot-time problems.

Third, the relative costs will continue to diverge over time. If you have to assume, the safe assumptions are probably: energy costs will continue to rise over time, hardware costs will decrease over time. So, even if this is break even now, this is a behavioral/cultural change, you need to start now so people will be doing it when the price benefits arrive, rather than suffering from a lag time.

The real costs to a power-down is that you have to close up all your windows and save your work. On my Macs, almost all my applications have an auto-save feature. For Windows, I usually use "hibertnate".

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