PCs with an ENERGY STARŪ label come with a power down feature for the CPU and monitor. ENERGY STAR-labeled computers have the capability to power down to a "sleep" mode, in which they consume 15 Watts or less power, which is around 70% less electricity than a computer without power management features. ENERGY STAR-labeled monitors have the capability to power down into two successive "sleep" modes. In the first, the monitor energy consumption is less than or equal to 15 watts, and in the second power consumption reduces to eight watts, which is less than 10% of its operating power consumption. These features allow you to set a time of inactivity at which the PC and monitor will power down into the "sleep" mode. Make sure you have the power down feature set up on your PC through your operating system software. This has to be done by you, otherwise the PC will not power down. If your PC and monitor do not have a power down feature, and even if they do, follow the guidelines below about when to turn the CPU and monitor off.
Note that screen savers are not energy savers. They may in fact use more energy than not using one, and the power down feature may not work if you have a screen saver activated. In fact, modern color monitors do not need screen savers at all.
The cost-effective time for when a PC should be turned off when you will probably be using it for most of the day is mainly a question of how much your time is worth. If takes a long time shut down the computer and then restart it later and get back into working mode, the value of your time will probably be much greater than the value of the amount of electricity you will save by turning it off. Most PCs reach the end of their "useful" life due to advances in technology long before the affects of being switched on and off ten or more times a day are likely to have a negative impact on their service life. They use about the same amount of energy to startup as they use when they are on for about two seconds. The less time a PC is on, the longer it will "last." PCs also produce heat, so turning them off reduces building cooling loads. (On the other hand, PCs are not a cost-effective source of heat during the winter.) Also, there is no more effective security firewall than not having the PC on.
A rule of thumb for energy saving is that if you are not going to be using your PC for more than about 20 minutes, turn the monitor off. If you are not going to be using your PC for more than around two hours, turn the CPU and monitor off. If you use your computer most of the time over say an eight-hour period, but have breaks for longer than 20 minutes up to an hour, just turn the monitor off when the PC is not in use, and be sure to use the power down feature! You should definitely turn everything off if you won't be using the PC for more than four hours.
The exceptions are if the PC has a very old hard drive, if the PC operates or monitors some other device such as phone/fax, printer, or home security system, and/or if the PC is part of network file sharing operation.
Make sure your computer is on a power strip/surge protector. When the PC is not in use for extended periods, turn off the PC with the switch on the power strip. Even when you turn some PCs off with the switch on the PC itself, it may consume a small amount of power. If you don't use a power strip, unplug the CPU and monitor.
Environmental Benefits
The environmental benefits of turning computers off are dependent on the source of the electricity you consume. Coal fired power plants produce about 50 percent of the electricity in the United States. Natural gas fired power plants provide about 15 percent, nuclear plants about 18 percent, hydro dams about 10 percent, and the rest is from oil (about 3 percent) and "renewable" sources such as biomass, geothermal, wind, and solar power plants. Fossil fuel combustion power plants (coal, gas, and oil) emit carbon dioxide, sulfur dioxide (mainly from coal and oil fired power plants), nitrous oxides, and particulates and heavy metals such as mercury (coal fired power plants). Regardless of the source of electricity, if you consume less, you are reducing the impact you have on the environment.
This fact sheet was reviewed for accuracy in March 2003.
Source: U.S. Department of Energy
