Computer off at night
Does it make sense to shut down and unplug my computer every night?
In my office a lot of my colleagues don't turn their computer off at night - it runs continuously 24 x 7, sometimes even when they go on vacation for weeks at a time. I've heard that it takes several coal power plants in the US alone just to keep people's computers powered when they're not using them. What are the facts here? I'd like to be able to argue to my workmates why they should turn their computer off at night and over the weekend but I don't want to give them a patchy argument for it.
Also, I know one reason people don't shutdown or hibernate when they leave work is that it takes a few minutes to reboot (or wake up from hibernate) when they get back the next workday. At the very least I guess they could set their computer into standby or suspend mode. How much electricity does that save?
Answer from Green Energy Efficient Homes
Turning a computer off at night or whenever you're away from it for more than a few hours is definitely a good idea from an energy and environmental perspective. To understand the impact let's consider a couple of types of computer: a small laptop and an older desktop (I don't know a lot of people who use newer desktops - most new computers seem to be laptops, but people do keep older desktops around and sometimes they stay on for long periods of idle time).
A modern laptop that is ENERGY STAR qualified typically consumes a modest amount of power - 15-40 watts from its power supply - while it's running. If the computer is relatively idle (which it usually is when not in use, and often is even when used for non-CPU intensive tasks like word processing or e-mail), it is still probably using substantially less than 40 watts. Assuming an 8 hour workday where the laptop uses, for argument's sake, an average of 20 watts, that works out to 20 x 8 = 16 watt hours, or 0.16 kilowatt hours per day. Since a kilowatt hour can be generated by burning approximately 1 pound of coal (see my energy saving facts page for more interesting numbers on energy equivalents), using your laptop for 40 hours a week and shutting the computer off at night or on weekends means burning about a pound of coal a week (and producing about 3 lbs of CO2 emissions a week). Over the course of a year that could work out to 50 pounds of coal burned, or 150 lbs of CO2 emissions.
Putting the laptop in standby mode instead of shutting the computer off at night means the laptop will consume just a few watts when not used - perhaps 4-5 watts on average (since the battery will lose some power in standby mode, so a little power is required to keep it charged). That adds roughly another 0.6 kilowatt hours per week if you turn the computer to standby, instead of shutting it down or hibernating it overnight.
Leaving the laptop on continuously for 168 hours a week works out to perhaps 3 kilowatt hours per week - 150 pounds of coal per year or 450 pounds of CO2 emissions. (168 x 20 watts / hour = 3360 watt hours or 3.36 kwh / week.)
You shouldn't find it too hard to convince your colleagues to turn their computer off at night if you can show them that a simple gesture twice per work day (power-up in the morning, hibernate or shutdown in the evening) can cut their CO2 emissions by 450 pounds per year. That's more than 2 lbs of CO2 emissions per workday - for a five minute delay in startup. Just tell them to spend those five morning minutes chatting with colleagues or grabing a coffee. That seems to me a pretty reasonable compromise for people to make.
The stakes are even higher for turning a desktop computer off at night. Desktop computers use quite a bit more electricity than laptops. Older ones and ones lacking the ENERGY STAR label can use upwards of 100 watts of power when turned on, even when not in use. For example, if you have a 3D screensaver running, the 3D manipulations it does actually consume a fair bit of CPU power and can increase the power draw. Even if the computer is just sitting there idle, it still draws power, as evidenced by all the heat coming out the fan vent.
If you do decide to turn your computer off at night by hibernating it, as opposed to shutting it down and later rebooting it, you may still find it needs to be rebooted every few days. In my experience, even leaving your browser open for long periods can cause large amounts of memory usage (this is caused by 'memory leaks' where the program forgets to properly free memory it is done using), and the more memory being used (whether for good purposes or because of a leak) the longer hibernation and wake-up take, because to hibernate the computer has to write out all used memory to a file on disk, and on wake-up it has to read all that data back into main or virtual memory.
I have an energy monitor called the Kill A Watt meter that lets me measure how much electricity a plug-in device uses. My very old desktop PC actually used about 30 watts when plugged in, even when it was completely shut down, because it was a cheap clone with a power supply that was always on. Higher quality desktop PCs don't typically have this problem - they draw no power at all when shut down - but they will still draw some wattage when in standby mode. (A desktop PC that is ENERGY STAR qualified is your best bet here as they have to meet strict energy consumption levels for each of their on, standby, and off states.) Obviously if you step away from your computer for an hour or two it's more convenient to put it in standby mode but if you're leaving work for the day it's more efficient to shut it down completely.
One way to help your office mates understand the value of turning their computer off at night is to plug their computer into a Kill A Watt meter and let them see how much electricity the computer consumes overnight. (Unfortunately they'll have to shut down or hibernate their computer before you can plug it into the Kill A Watt meter, which sits between the device being measured and the wall outlet. They can reset the Kill A Watt meter so it starts measuring kilowatt hours consumed from the moment they leave at the end of the day.) Assuming a regular 40 hour work week, and that you measure the computer energy usage from quitting time until the start of the next morning, you can easily figure out how much energy they are wasting by leaving their computer on overnight.
The other thing to point out to your office mates is the impact of their actions when multiplied by hundreds of millions of other office workers. Turning one computer off at night may only save a hundred kilowatt hours a year, but that 450 pounds of CO2 emissions, when multiplied by the hundreds of millions of office workers in the world, turns into a vast amount of unnecessary emissions - perhaps 100 million tons of CO2 emissions that could be eliminated by not leaving computers running constantly. (We are of course assuming, for argument's sake, that all the electricity to run these computers comes from coal-fired power plants, but in many US states it is the case that most or all electricity is generated from coal.)
If someone told me I could easily be part of an effort to cut a hundred million tons of CO2, just by taking my morning coffee break at the start of the business day while my computer started up, I'd be game!
Reader comments
G.S. Hudson - Nov 8 2009: While I applaud the effort of the answerer of this question, his numbers are not consistent with what I have measured. My Kill-o-watt indicates my PC uses:
- 240 watts when booted up
- 180 watts in "Standby"
- 25 watts in "Hibernate"
- 25 watts when "Off"
- 0 watts when turned "Off" at the powerstrip.
If 100 million Americans set their computers to Hibernate overnight, it works out to 288 million kWh of electrical waste every day.
My Dell takes only 15 seconds to come back after hibernating, so I don't even have time to get coffee.
Keep up the great work!
Robin from Green Energy Efficient Homes - Nov 13 2009: Thanks for your Kill a watt readings, G.S. I guess it depends on the computer. I lent my Kill A Watt meter to a friend a while back and he has misplaced it during a home reno, so I can't do an actual reading of my IBM ThinkStation desktop right now, but I did do readings of a number of PC's at work a few years back, and 50 watts for the computer itself was pretty typical. (If you add in a monitor, printer, router, and modem, and all of them are left on, you can easily get to 250 watts though.)
If your reading is for your PC only (not the screen or peripherals) it seems to me that you have a rather inefficient PC. A computer that consumes 25 watts when off probably has a cheap power supply; a good power supply should consume nothing or at most 1-2 watts when powered off. And 180 watts in standby sounds much too high as well. As for 240 watts when booted up, you could probably do considerably better with a more energy efficient power supply.
On the other hand, most people will buy the cheaper of two PC's with the same performance features, since energy price tags aren't included in the up front cost and people don't even realize how inefficient some PCs are, so it may well be that the majority of North Americans have juice-guzzling PCs that use quite a bit more than what I've measured. I would recommend everyone by an ENERGY STAR qualified PC as these should have much lower consumption in each mode (running, standby, hibernate, off) than what you read above.
Either way (your readings or mine) the fact remains that there's a lot of energy wasted leaving computers on, and the amount of electricity wasted (and coal needlessly burned) is rather tragic.
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