Computer energy usage

How to reduce computer energy usage while the computer is left on

So your computer runs all the time. How can you cut computer energy usage while it's on? Assuming there really is a good reason to keep it running, what can you do to save the most energy?

Let's say you're downloading a large piece of software you have purchased, and the download is running slowly. Or you're running BitTorrent or Limewire to download a file. There are a number of reasons why you might feel you have to leave the computer on overnight. How can you cut computer energy usage in these cases?

The first thing you need to ask is whether this is really necessary. For example, consider the case of illegally downloading a movie on BitTorrent. As a published author and website owner I do not condone violating anyone's copyright, but people do it all the time. If you really want to cut your computer energy usage, perhaps ordering the movie to be mailed to you makes more sense. Consider this:

A download that takes 8 hours, running on a desktop computer, could use up to 130 watts of power continuously counting the computer, cable/DSL modem, and router assuming both modem and router are required. Over an 8 hour period that works out to over 1 kwh of electricity. If generated from coal, that's the equivalent of burning a pound of coal to fuel that download.
Keeping your computer on for those 8 hours, if you weren't doing anything else with the computer, also means wear and tear on computer components, especially the hard drive. Movie downloads involve constant reading and writing of snippets of a large movie file, and those snippets can be scattered all over a hard drive, which means the head is bouncing all over the place. A good way to shave years off the life of your hard drive, which means in the long run downloading the movies will cost you even more.
You'll also increase fragmentation on your hard drive, which means more defragmentation runs, again using more energy and causing more wear and tear on the drive.
Finally, don't forget that your own time has value. If you are constantly searching for new movies to download, checking whether what you downloaded actually worked (and is what it says it is), and trying a new torrent when the one you got 80% of turns out to be useless, you could well use up much more time than it would take you to walk to the local video store and rent the DVD.

As you can see, I don't think the economics of downloading movies make much sense, unless you don't pay anything for your electricity, someone else pays for your computer, and your time isn't worth much. I guess that's why so much downloading is done by teenagers - their parents pay the costs, and the kids' time may not be worth much money if they're not working.

Anyhow, let's assume you're doing something legal and necessary that requires you to leave the computer running overnight or for long periods, and you want to cut computer energy usage while doing so. What can you do? Here are five tips:

1. Choose the lowest power setting in your Control Panel > Power Settings choices, but don't have the hard disk turn off after idle. You may need the hard disk active in order to read or write data while the program you are running is slowly churning away. If the activity your computer is doing is waiting on the network (e.g. downloading files) your CPU can be slowed down. Slow it to the minimum, it really doesn't take much CPU activity to download a file at a transfer rate of a few kilobytes or even 100 kilobytes per second, since it's mainly I/O.

2. Set your screensaver to blank. Don't have any animations. I've done measurements of some of the screensavers and they actually increase power consumption slightly because the CPU has to do more work to animate the screen. This is true even if the monitor is turned off - the screensaver is still writing the animation to the screen buffer even with no monitor on. That takes CPU cycles that cost extra energy.

3. Close any applications that periodically access the network or do backups to disk, such as e-mail applications or word processors / spreadsheets. They will use a bit of energy (we're talking tiny, tiny amounts here.)

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4. Unplug the power supplies for all peripherals not needed for the activity that requires your computer to stay on, including speakers, printer, scanner, etc. For network activities you would need your cable/DSL modem and your router of course, but you'd save even more if you just plugged your computer straight into the modem and turned off the router, assuming you don't need it for another device. Remember that power supplies (AC/DC converters) may use energy when plugged in, even if the device they are attached to is turned off. Using an Ethernet connection instead of a wireless connection will probably also save you a bit of energy.

5. Check the computer periodically to see if the activity requiring the long runtime is complete, and power off when it's done. There's no point in doing all the other stuff if the computer winds up staying on for hours after the long-lasting run finishes, and isn't being used for anything else. In fact if you want to get totally into cutting your computer energy usage to the minimum, you could check the estimated completion time of the long-running task, and set your power options to have the computer go into hibernation one hour after the estimated completion time of the task you're running.

6. Turn off your display! If you're just running a download you don't need to keep the display on. Note that if you do have the display on because you are using it, you can also save energy by lowering the brightness of the display, or for a CRT monitor, you can also use darker backgrounds which use less energy. For LCD displays, the energy consumption of the display is not affected by the colors being displayed, because LCD display energy use comes from the backlighting of the display; the Liquid Crystals in the Display just determine which colors of light to let out. Whether your LCD has a black or white background it will use the same amount of electricity.

You can measure your computer energy usage with an electricity usage meter such as a Kill-a-watt meter, which you plug into the wall, then plug your computer power bar into that. I used mine to test all the different parts of a desktop computer to see where the most energy use was, and to test different power settings, screen savers, etc. This is only about a $25 investment and can be used all over the house; it almost always pays for itself in savings within a year.

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