This is the third installment in a series of articles addressing PSU efficiency. Article one focused on a theoretical new server, article 2 on a typical desktop PC. This article will focus on a current real server, and introduces a new PSU — an 80+ platinum model.
The system spends a lot of time semi-idling (serving network and disk requests but not doing too much CPU work). I estimated that it would pull around 150W on average, and then calculated it below. It really did come out exactly like that!
|Base system Sempron LE-1100 (1.9GHz single-core) on nForce 630i / 7050 motherboard. 2Gb DDR-II||35W|
|2x Samsung F4 2Tb HDDs, 7x 1Tb Green HDDs inc. WD Green 1Tb, Seagate 1Tb and Samsung 1Tb, 1x WD 750Gb 7200rpm drive, 1x Maxtor 300Gb 7200rpm drive, 1x WD 200Gb 7200rpm IDE drive||108W|
|Areca 1220 RAID Card||5W|
|2x 120mm Case Fan||2W|
Out of interest, assuming a cost of £0.10 per kWh this system would cost a total of £131.50 a year to run even with a perfectly efficient PSU!
The ATX specification requires 70% efficiency. Below is a comparison between a bare minimum ATX PSU and a few highly efficient PSU’s.
The figure for the generic PSU is based on the minimum requirement and is therefore a worst case. I have calculated a best-case yearly saving, based on a kWh charge of 10p and assuming 24.7 usage.
|Make / Model||Efficiency at 150W||Est. A.C. power draw||Saving|
|ATX v2.2 250w ATX||70% (at 150W)||215W|
|Enermax Modu87+ 500w||88.5%||169W||£39.89|
|Kingwin Lazer Platinum 550W||93.3%||161W||£47.54|
|HuntKey Jumper R90 300W 80+ Gold||90%||167W||£41.74|
Conclusion: This is the first scenario where new higher-efficiency PSUs are reasonably price competitive based only on power usage. For such a system, a high efficiency PSU will pay for itself within approximately 3 years. If you plan to keep the system for more than 3 years a high efficiency PSU is a worthwhile investment as its TCO will be lower. As energy prices continue to rise this TCO advantage will widen.
Added the HuntKey Jumper R90. This PSU changes the conclusion conclusively. It produces savings of over £40, which is at least the price of the PSU! A payback period of 1 year, with an expectation that electricity prices will continue to rise is well worth the investment.
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