How much does it cost to leave your computer on overnight?

[OS]

That 2 weeks number is flat out wrong. If it were true, you could leave a laptop on for almost two weeks after charging the battery while the computer was still on. Anyone who has owned a laptop before knows how incredibly false that is, most laptops never make it to 3 hours. And also, laptop owner would notice that their battery life would be nonexistent if one were to keep turning it on and off. But I've owned a laptop before and how many times I turn a laptop on and off has almost no effect on battery life.

Hmm, I see Eug did a far far better job explaining it than I did. Besides, I wouldn't trust any mac consultant, looking and pretending to be smart is different than actually knowing what you are talking about.

 

[Linux23]

I heard it equals to a year, not two weeks!

 

[Muerto]

If you think about it your computer has to do much more work when it's starting up than when it's sitting idle on your desk.

Your hard disks need to start spinning, putting an object into motion requires much more work than maintaining motion. If your hard disk spins at 5400 - 7200 rpm, and reaches that speed in a few seconds, think about how much energy is required.

Your CPU needs to retrieve all the files necessary to boot the system. Obviously none of them are in the system memory so they must all be found and loaded from the hard drive.

All of your other system components need to be initialized and checked during the boot sequence. So your computer is performing many complex tasks simultaneously and trying to complete them ASAP. This leads to an enormous power comsumption, much more than is needed to keep it running idle, especially overnight when it's not doing anything.

 

[RentaCow]

OMFG!!! I CANNOT believe how gullible and nieve some of you people are!

A computer DOES NOT use more power on boot up than it does in two weeks of regular continuous running...

I'd bet my life on that one.

For the sake of humanity, do this experiment if you even for a second thought what zippy was claiming is true. Take a regular AC amp meter and measure the current that your computer draws when it first turns on (including monitor). Then, continue to watch the amp meter until your computer is fully "on."

This is what you will find. Upon first turning it on (within 1/2 second of flippin' the switch) you will see the Amp meter surge up to a high value such as 3 amps at 115 volts. Then, almost instantaneously (less than one second after flipping the power switch) it will drop down to about 2 amps or less at 115 volts (depends on how much power your particular monitor and computer combo require, but two amps is a good number).

Even if we vastly overestimate the time required for this "surge" in current being drawn to be 1/2 second, that works out to be: 3ampsX115VoltsX1/2Second=172.5 Watt seconds of electricity used

In the following two seconds the computer draws: 2ampsX115VoltsX2Seconds=460 Watt seconds of electricity!!

Jezus people, a computer will draw more power in the two seconds following initial start up than in the initial startup period. Two weeks! Good grief!

Trust me I know what I am talking about... I'm an electrical engineer, and I have actually conducted this exact experiment before.

A computer does NOT draw considerably more power during boot up than at idle either. At idle, the only power saving feature likely to be running is the HALT instruction on your processor. Since processors these days don't draw anything more than 55 watts, you can't expect to save anymore than ~50 watts by running the HALT instruction near continuously (like at true idle). Considering that a whole computer plus monitor can easily draw ~200 watts, we arn't talking about TOO much of an overall decrease during idle/CPU HALT (compared to boot up where everything is running).

 

[Muerto]

RentaCow,

Instead of Watt Seconds why don't you just say Joules? They're the same thing aren't they?

 

[zippy]

Ok, I will call him tomorrow and ask for an explanation...this was my sister relaying this message...it is possible that she meant something else. I will figure out what is up, because I was (and still am) quite skeptical of it.

 

[luckynkl]

Leave the computer on. The initial start-up does consume more power than leaving it on. I'm sure after a period of time, leaving it on will eventually consume more power - if you use your computer once a month or something! But consider if you power your computer on and off each day. In a 2 week period, you will consume much more power turning it on and off each day than if you simply left it on for 2 weeks. That is the factor that you'all seem to have left out. You're only considering turning the computer on only once time during a 2 week period. So experiment:

Turn on computer. After it's completely booted up, turn off. Measure energy consumption.

Turn on computer leave on for 2 weeks. Measure.

The latter will consume more energy. And you'll get to actually use your computer.

The former will consume less energy - but hope you didn't actually want to use the computer!

OIC, you actually wanted to use your computer! Now turn it on and off each day and watch that ole electric bill rise!

Let's consider the simple light bulb. Ever have one simply burn out while you're right in the middle of reading a book? I never have. Light bulbs burn out when you turn the switch on and then pop! Power surge! BTW, Tom Edison's original light bulb does still work. They had to mess with it or they wouldn't have made any money!

Most electronics you want to run as much as possible such as your TV set, etc... The exanding and contraction due to heat and cold from turning it on and off does adversely affect electronics - and your computer. I've actually blown a few computers turning them on and off all the time. The ones I leave on last forever.

Same thing with your car. The more you run the car (as long as you properly maintain it) the better for the car. The heat burns off all that crap out of your engine. The last thing you want is a car from that little old lady from Pasadena that only took the car out for a mile each month. The gunk that has accumulated in the engine will make the car short-lived.

 

[WoundedWallet]

It seems like the voice of wisdom has spoken.

 

[ThunderbirdsAreGO]

So you leave your car running in idle during the night, to minimize fuel consumption and wear, and to be able to drive away immediatly in an already warmed up car in the morning?
There has to be a break-even point, but two weeks?

 

[Jhhnn]

How much does it cost to leave your computer on all night? Depends... on a lot of things. Enabling APM on windows machines and adjusting it for maximum savings cuts the power consumption way down, and ACPI is supposed to do an even better job. The only scientific way to tell is to use an a/c amprobe and measure the line cord amperage in whatever power saving mode you use, and multiply it out by the price and time period. I would guess that it costs a few cents per night if you are properly set up. Your local electric utility likely has excess capacity at night, its not like you're going to cause a brownout.

 

[zippy]

I'll be calling him at around 3PM EST (he should be home then)...it is quite possible that he meant this for the average user. The average computer user is on their computer for an hour or two a day...if they let it hibernate (just enough power so it can come back on) till the next time the use it...

I think it does make sense, but not to us geeks who are on the computer 4-9 hours a day play Q3a, UT, HL TFC, with 3403 case fans and an alpha in our machine to suppress our highly overclocked chips.

 

[Relf Lauren]

Hey zippy...

My computer has that "power saving" feature too.....HDD spins down, less CPU usage, etc...

I am wondering, with all of the above factors AND turning the monitor off, the computer should almost "no" power at all, right?



Relf Lauren

 

[zippy]

I would think so.

 

[Terp]

My sister told me it was cheaper to leave everything on, so I now never turn off the radio, TV, computer, stereo, vacuum cleaner, light fixtures, oven, etc, etc....Sure, it's a little noisy around here now, but I'll do anything to save a buck

 

[Sir Fredrick]

Yes, there is a break even point. With a car it's 20 minutes. Yes, you consume as much gas starting your car as you do letting it run idle for 20 minutes. Where did I learn this? In the sunday paper quite a while ago...from Beakman and Jax (don't laugh).

 

[Terp]

That analogy is true, Sir Fredrick, but not the same for electricity...a car has to consume more gas to turn the engine over as opposed to running idle...the gas has to make it's way from the tank, to the carb/fuel injectors, cylinders, etc....and takes some serious cranking power to get the juices flowing. With electricity, however, the power is there at the outlet already waiting...

...apples and oranges

 

[Sir Fredrick]

Ok, how about an analogy that uses electricity. At my school (Eckerd College, located in St. Petersburg, FL), they leave the air conditioning running all year round, even though they could make the students happy and turn it off for the winter (it does get cold down there in the winter...), they have decided to leave the AC on all year, because it uses less energy than it would if they turned it off when it got cold.
I had to tape up my vents because it was so cold with the AC.

 

[HaVoC]

Analogies to cars and AC systems are not valid. They are totally different systems. My personal opinion is that starting the computer does consume more power than constant run, but not 2-weeks worth. With todays high-power processors, fast HD and large monitors, I think it is worth turning your computer off at night. I read somewhere that with modern components, there is no concern about power cycling problems, etc, as long as it is reasonable.

Turning off the monitor is probably the single most energy savings, and this is good because leaving the monitor on also reduces the life of it. Sleep mode or hibernate is good as well.

BTW, I've taken a trip to Europe and seen how efficient the Germans and other Europeans are when it comes to per-capita energy usage. Though sometimes it gets ridiculous (timed light switches that turn on for 10 secs and then leave you in the dark climbing steep stairs...arrgg. :|) but generally I think it is sad us Americans consume so much power.

 

[Terp]

I would opt for a garden hose analogy, as household water is much like household electricity insofar that it is at your disposal the second you plug something in, or turn on the faucet...since it takes extra water to fill up the hose, much like the extra power to power a computer for the first boot cycle, would you argue that one would consume less less water by leaving the garden hose on for two-weeks, or turning it off when you are done with it?

 

[Sir Fredrick]

Terp, the water stays in the hose when you turn it off. A better analogy would be if every time you wanted to water your lawn, you had to fill an empty olympic sized pool with your garden hose, and ocne that was done you could proceed to water your lawn. Then it might be more efficient to leave it on for 2 weeks straight, especially with flow regulators that would allow you to have it just drip a little or flow full stream depending on your needs (i.e. sleep mode)

Anyway, that's a much worse analogy than the car or AC.

I agree though that none of the analogies quite match up, but it does show that it takes more energy to start somethign up than it does to leave it running. Same applies to computers, though obviously the amount of energy used for startup is going to be very different.

 

[Terp]

1.) I never leave water in my hose 2.) If I wanted to water my lawn, why would I fill a swimming pool?

Okay, okay, I give....going to fire-up the grill, shut my computer down for the night, and save some energy!


....should I leave my grill on when I am done with it, since I'll be using it again in a few days?

 

[Eug]

Do the math guys. Simple high school math.

I have a simplistic calculation above, because it is a simple problem. I'd be surprised if bootup used 1/3000th of the power of 2 weeks idling (with no power-saving features).

RentaCow said it most succinctly. If the 2 week analogy were true, you'd be able to leave your laptop on for several months. Indeed, with a 4 hour battery life, with the completely illogical 2 week analogy, you wouldn't be able to even turn on the laptop once. You may say, well, it has enough juice to turn it on and then run four hours. Well then, the battery would not be able to turn on the laptop twice. Sheesh.

 

[Terp]

Yea, what he said!

This sounds like a question for Maxwell Smart, the author of an old book entitles, "Straight Dope." He claims to be the leading authority at answering questions out of the ordinary...everything from "What came first, the chicken or the egg" ...to why the shower curtain always pulls in when you turn the hot water on in the shower ....and my favorite, "Can you kill a female from blowing into her v*gina." The answer is yes, the air could get trapped and cause an aneurysm in the bloodstream, although it is very rare....if he doesn?t know the answer offhand, he'll research it and get back to you within a few weeks...I'll ask him and post back here, although most of us know the question is a rhetorical one.

 

[OS]

What is with this fetish for finding analogies? There simply isn't an analogy that works for this situation, geez, drop the analogies already. And for those you who still think what zippy said is true, call your electric company and ask them to lend you an ammeter (I hear they do it for free) and see if it's true.

 

[eelw]

I work at the local hydro company, (not as a power engineer but in the IS dept.) They have portable power metres available for customers to test appliances at home. I decided to borrow one once. As RentaCow mentioned, there is only a minor power surge as you power on your computer. The biggest culprit is of course the monitor. The wheel in the metre went crazy when you power on the monitor. It spun at least 5 times the normal operating speed, lasted only about 2 seconds. So take it from someone who has actually tested this, there is no significant difference in power consumption if you turn off your computer many times during the day. FYI, I tested the power consumption of my clothes iron. My iron used more power in 10 minutes of use, than my computer plus monitor during a day of use.