Should I switch my computer off at night?


This is an extract from an article by Monte Enbysk on the Microsoft Small Business Centre website.

(note: for comparison, a normal light bulb in your home uses between 40 and 100 watts)

Here are some consumer "myths" that are worth addressing:

  • Turning your PC off uses more energy than leaving it on. Not true. The small surge of power you use when turning it on -- which varies per PC make and model -- is still much smaller than the amount you use in keeping it on for lengthy periods.
  • Turning your PC on and off wears it out. A decade ago, there was something to this, but not today, say Hershberg and others. It used to be that PC hard disks did not automatically park their heads when shut off, and that frequent on/off cycling could damage the hard disks. Today's PCs are designed to handle 40,000 on/off cycles before a failure, and that's a number you likely won't reach during the computer's five-to-seven-year life span.
  • Screen savers save energy. Not true. Screen savers, at a minimum, can use 42 watts; those with 3D graphics can use as much as 114.5 watts, according to Don McCall, a Dell product marketing manager who does power measurement studies for the PC manufacturer. "It's absolutely wrong thinking that a screen saver will save energy," he says.
  • Your computer uses zero energy when "off." That's true only if it is unplugged. Otherwise, the PC utilizes "flea power," or about 2.3 watts, to maintain local-area network connectivity, among other things, McCall says. In "hibernate" mode, your PC uses the same 2.3 watts; in "sleep" mode, your PC uses about 3.1 watts. Monitors do use zero energy when turned off.

Lab tests done by Dell show that a PC running Microsoft Office Small Business 2007 uses 42.7 watts, McCall says. If it runs continuously at that rate for 365 days, at 7 cents per kilowatt-hour, the power consumption costs would be $26.18 for the PC and $45.99 for a regular monitor, for a total of $72.17 for the workstation.

Flat-panel monitors use less energy (22 watts when left on, 3.3 watts in "sleep" mode) than regular monitors (75 watts when left on, 5 watts in "sleep" mode), McCall says. So the same workstation with Microsoft Office running for a year would use $39.67 in power with a flat panel.

Meanwhile, if a PC was kept in "sleep" mode for 20 hours, for every four hours "on," as Dell recommends, the annual energy costs per PC would total $16.17 with a regular monitor and $9.88 with a flat panel. Using "hibernate," the costs would be slightly cheaper.

So what should I do?

  • If you are not going to use your computer in the next 24 hours, or longer, shut it down and switch off at the wall plug, or unplug it completely.
  • If you are not going to use it for a few hours, or are shutting down for the night, and you want to resume with all your programs running, use the hibernate or sleep modes, which consume very little power, but allow you to get going again quickly. If you have a separate monitor, switch it off.

What is "Hibernate" mode?

In Hibernation mode, the current state of your computer (ie. all open programs & files) is saved to disk and the PC is powered off. There is no electricity consumed if you also switch off at the wall or unplug it. When you power it back on again, it boots much faster and your previous state is restored so that you can continue working as before.

You can select "Hibernate" from the shut-down screen on your computer (Windows 95, 2000, XP or Vista)

Hibernate from shut-down screen

What is "Sleep" mode?

Windows Vista has an advanced hibernate mode called Sleep mode. In Sleep mode, the power supply to non-essential and non-critical component is withheld, and most system operation is shutdown and stopped. All data in physical memory (RAM) is still kept, and the whole system is placed in stand-by mode, which can be woken up and used almost immediately. In Sleep mode, the power load is reduced considerably, saving a lot of energy. However, the power must not be cut off, and must be continued to be supplied to the computer in order to preserve the data stored in memory. Once out of power, the system will have to start again just like a freshly booted computer.

Windows Vista has an enhanced sleep mode so that on laptop / notebook computers, sleeping computers will automatically hibernate when battery power level is low. It also has a built-in Hybrid Sleep mode which ensures that the system state is preserved when power is lost.