How to Buy an Energy-Efficient Personal Computer
Information about energy-efficient personal computers in this section includes the following:
| Efficiency Recommendation Cost-Effectiveness Example Where to Find |
 |
Buyer Tips Usage Tips For More Information |
Also provided is a portable document format version of How to Buy an Energy-Efficient Personal Computer (PDF 67 KB, 2 pp). Download Adobe Reader.
| Efficiency Recommendation | |
|---|---|
| Maximum Continuous Power Supply Rating (or system type) |
Recommended "Sleep" ModeaPowerb |
| <= 200 watts | 15 watts or less |
| 201-300 watts | 20 watts or less |
| 301-350 watts | 25 watts or less |
| 351-400 watts | 30 watts or less |
| >400 watts | <= 10% of maximum power supply rating |
| PC/Monitor (all in one) | 35 watts or less |
a "Sleep" mode refers to a low-power standby condition, which is entered automatically after a set period of inactivity. The computer's active mode is restored when the user touches the mouse or the keyboard, or in response to a network signal.
b For computers shipped with networking capability that require the processor or memory to be involved in maintaining the network connection during sleep mode, the recommended sleep mode is 15% of the maximum power supply rating.
| Cost-Effectiveness Example | ||
|---|---|---|
| Performance | Base Model (No Power Management) |
Recommended Level (Power Management Enabled) |
| Annual Energy Use | 252 kWh | 133 kWh |
| Annual Energy Cost | $15 | $8 |
| Lifetime Energy Costa | $53 | $28 |
| Lifetime Energy Cost Savingsb | — | $25 |
a Lifetime energy cost is the sum of the discounted value of annual energy costs based on average usage and an assumed computer life of 4 years. Future electricity price trends and a discount rate of 3.4% are based on Federal guidelines (effective April, 2000 to March, 2001).
b These savings do not include the benefit from reduced air-conditioning costs, which depend on location and building type.
Cost-Effectiveness Assumptions: Computer model used for above example: Desktop PC, 500+ MHz, 300W Power Supply. Annual energy use calculation is based on typical office operating practices, including a 9.5 hour work day (in active use 4 hours/day) and 250 work days per year. Model assumes that 76% of personal computers are turned on during a typical business day and 35% left on overnight and on weekends. Assumed electricity price: $0.06/kWh, the Federal average electricity price in the U.S.
Where to Find Energy-Efficient Personal Computers
The Federal supply source for energy-efficient computers is the General Services Administration (GSA). GSA's on-line ordering system, GSA Advantage!, can be used to select and order computers. Make sure that the model you order qualifies for the ENERGY STAR® label. All ENERGY STAR® computers meet this efficiency recommendation.
When contracting or buying from a commercial source, specify or select a model with the ENERGY STAR® label. Visit the ENERGY STAR® Web site for a list of complying models.
Buyer Tips
Make sure that your PC power management features have been enabled by the supplier or installer, and are compatible with your monitor, software, and network (see LBNL's User Guide).
Laptop PCs offer many of the same features as desktop models, plus portability. However, combining a laptop with an external monitor or docking station will increase power use.
Usage Tips
Use your computer software to set the "idle time" delay to the shortest period consistent with your needs (for example, switch to sleep mode after ten minutes).
Even for PCs with a low-power sleep mode, you can save more energy and possibly extend your computer's lifetime if you manually shut it off completely at night, on weekends, and during long periods of non-use during the day. If your networked computer(s) must stay on and connected at night for file backup or other purposes, make sure the monitor is shut off. Look for network features that provide a timed shutdown, automatic shutdown after file backup, or alternatively, auto-boot-up before backup. Using sleep and off modes will not shorten your PC's lifetime.
Plug-in power supplies for laptop PCs typically use 15 watts or less but cannot be shut off completely. To save energy, unplug your power supply after the laptop battery is charged, or use a power-strip with an on-off switch.
Many laptop PCs (and some desktops) offer a "hibernate" or "bookmark" feature, which saves active programs and files before shutting off, then restores the same status when the PC is turned on. This added convenience encourages users to shut off their computers when not in use.
For More Information
- Environmental Protection Agency (EPA) has ENERGY STAR® product listings. EPA's ENERGY STAR®-labeled office equipment home page has several downloadable guides to help users optimize energy savings from office equipment.
Phone: (888) STAR-YES (782-7937) - TCO is a labeling program for computers, monitors, and other office equipment that includes energy efficiency, environmental and ergonomic criteria, as well as low electro magnetic emissions.
Phone: (312) 781-6223 - Lawrence Berkeley National Laboratory publishes the User Guide to Power Management for PCs and Monitors (PDF 207 KB, 72 pp). Download Adobe Reader.
Phone: (510) 486-7089 - Lawrence Berkeley National Laboratory provided supporting analysis for this recommendation.
Phone: (202) 646-7950