What is “efficiency”?
Efficiency is the ratio between the useful output of an energy conversion device and the input. For example, if your computer uses 300W, but pulls 400W from the wall, then the efficiency is 300W/400W, or 75%.
Computer power supplies are typically 75% efficient, especially those units included with computer chassis or units made more than a couple of years ago before power supply efficiency was made such a priority. The BFG GS, LS, MX and ES power supplies are typically 80% efficient or better.
Why is efficiency important?
Quite simply, if your power supply is more efficient, your computer will use less power. Depending on how much you pay for power from your utility company and how much power your computer typically uses, you can save anywhere from $1 to $10 per year, per computer… perhaps more!
Furthermore, because any AC power that is NOT converted into DC power is exhausted as heat, a more efficient power supply inherently runs cooler. Not only does this mean your office is going to be cooler, but also allows the power supply manufacturer to use a slower, quieter fans to cool the power supply.
Aren't higher wattage units less efficient at lower loads?
With all things being equal, yes. But you can't always compare brand A with brand B and assume that because brand B is a higher wattage that it's going to be less efficient at lower loads.
It is true that most power supplies are only at their most efficient when the load on them is 20% or more of their capability. So with conventional power supplies, you pretty much have to throw any kind of green initiative out the window when trying to buy a power supply that will allow for future expansion; like buying a second graphics card for SLI or adding more hard drives to run a RAID array.
Of course, even conventional power supplies vary from unit to unit, and since the initiative to be more efficient is a relatively new concept be aware that even if a modern day computer power supply is only 80% efficient from loads of 20% and up, it may be 77% or 78% efficient at a 10% load and this may still be much more efficient than the power supply you're replacing, even at it's best efficiency!
What is 80 Plus?
For a fee, 80 Plus will test your company's power supply to confirm that is over 80% efficient at 20%, 50% and 100% loads. Recently, 80 Plus expanded to include bronze, silver and gold certifications for power supplies that are over 82%, 85% and 87% respectively. Naturally, because of multiple PSU companies sharing the same platform and the cost of certification, the list is not all inclusive... but it's a heck of a brilliant start:
http://80plus.org/manu/psu_80plus/psu_join.php
03-28-2008
Power Supply Efficiency FAQ
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