The Cost of Running Your PC
by Christoph Katzer on November 14, 2008 3:00 AM EST- Posted in
- Cases/Cooling/PSUs
Actual System Power Costs
On the previous page, we estimated the efficiency for each system as being 82%. Obviously, that's not a true way of calculating power requirements or efficiency. Now we're going to shift to the real world and see what the three sample systems end up costing on an hourly basis.
Before we get to the tables, it's important to remember that just because a power supply advertises 90% efficiency doesn't mean you'll always reach that level. You can look at any of our power supply reviews -- or just read Debunking Power Supply Myths -- to understand this better. The short summary is that all power supplies have an efficiency curve, which depends on the load you place on the power supply.
At lower loads and maximum load, efficiency is lower than if you run at a medium load (relative to the PSU's rated output). If you're just surfing the Internet, writing a document, or viewing pictures your system will largely sit idle. Playing a game, doing 3D rendering, encoding a video, or other complex calculations will place a higher load on your PSU. The following tables use actual efficiency with a real power supply to calculate power costs.
System 1
Our entry-level system, System 1, will utilize the Thermaltake TR2 QFan 300W power supply we recommended in our last article. System 1 consumes 90W to 140W of power, depending on load -- those are best-case/worst-case figures. We haven't posted our review of the QFan yet, but it achieves 82% efficiency at 90W load and 84% efficiency at 140W load. The hourly power costs are:
| System 1 Power Costs with Real Efficiency | |||||
| Load | Efficiency | Outlet Power | Cost/hr NC | Cost/hr CA | Cost/hr GER |
| 90W | 82% | 110 | $0.008 | $0.014 | €0.024 ($0.031) |
| 140W | 84% | 167 | $0.013 | $0.021 | €0.037 ($0.048) |
System 2
System 2, our midrange system, will use the OCZ ModXStream Pro. This system requires between 160W and 350W of power. The OCZ power supply runs at 84% efficiency for 160W and 85% efficiency for 350W. That gives the following power costs:
| System 2 Power Costs with Real Efficiency | |||||
| Load | Efficiency | Outlet Power | Cost/hr NC | Cost/hr CA | Cost/hr GER |
| 160W | 84% | 190 | $0.014 | $0.024 | €0.042 ($0.054) |
| 350W | 85% | 412 | $0.031 | $0.053 | €0.091 ($0.118) |
System 3
Lastly, our high-end system is running two graphics cards for maximum performance. This time we selected the OCZ EliteXStream 800W PSU. Note that even this beefy system still only requires 550W at maximum load, whereas it idles at 310W. In this case, efficiency is 84% idle and 83% at full load.
| System 3 Power Costs with Real Efficiency | |||||
| Load | Efficiency | Outlet Power | Cost/hr NC | Cost/hr CA | Cost/hr GER |
| 310W | 84% | 369 | $0.028 | $0.047 | €0.081 ($0.106) |
| 550W | 83% | 663 | $0.050 | $0.085 | €0.146 ($0.190) |
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Kyanzes - Friday, November 14, 2008 - link
I've kind of anticipated a calculator but still a nice read.JarredWalton - Saturday, November 15, 2008 - link
Isn't that what the spreadsheet is?vandaliser - Friday, November 14, 2008 - link
All you had to do is buy a Watt Meter which is kind of like a surge protector (but with a digital reader) where you connects your PC's power plug to the meter, then the meter to the main. (just go to ebay search Energy Meter and you will know what I'm on about)Take the reading in watts, divide it by 1000 to gives you the number of kwph. Finally, multiply it by the cost of one kwph on your electricity bill and numbers of hours you want to run it for.
I'm not sure about their expected cost of running, but it actually surprises many people that their PC uses a lot less power then what they expects.
Griswold - Friday, November 14, 2008 - link
Just that truly el-cheapo equipment will give you horribly wrong readings (cos-phi anyone?). Not saying a "watt-meter" must be expensive to give you acurate readings for home use, but there is way too much junk on the shelves out there.Souka - Friday, November 14, 2008 - link
Buy a Kill-a-watt meter of eBay.... I did years ago, still using it today.It'll show real time Amps, Volts, Watt load, KWhr used, and time.
http://energyseeds.com/2007/10/11/go-solar-and-kil...">http://energyseeds.com/2007/10/11/go-solar-and-kil...
I just pulled it out for a co-worker to try at her home. :)
DeepThought86 - Friday, November 14, 2008 - link
Given how little power even beefy systems consume, why is it that Anandtech continually reviews rediculously overpowered PSUs? What % of the market is made up of those 600W-1000W monsters? How about comprehensive reviews of the 300-500W marketanartik - Tuesday, November 18, 2008 - link
I would have to say that is a common misconception... There are reasons to buy more power than you "need". I bought "extra" for future upgrades and headroom. The problem with the calculator is most people plug in and come to the conclusion they need some fixed amount of power. All power supplies degrade in output over time with the cheaper ones faster (or use misleading claims as to output in the first place). If the calc says you need 400 and you buy 400 you’re in for trouble as the output deteriorates even quicker from running it at full capacity. The more you strain the PS the hotter its going to run and the louder its fans get. Plus you decide to run out and buy the latest power sucking hardware and voila you need a new power supply.I have a 4.3ghz E8500/X48 (SB w/bay,2 sticks DDR2, 2x drives,1 dvd burner and 3x120, 3x140) system and according to the calc I only need 462 with my current OC'd 8800 GTX. My old 550 Antec couldn't hang, screeched harmonics and was replaced with a Corsair HX1000. If I did a worse case upgrade... OC'd Q9550, more HD's, bluray burner and either a single 4870 X2 or possibly two and that power jumps to the range of 650-850 on paper. Factor in overages for peaks, efficiency, deterioration, percent utilization and it ranges from in the ball park to pushing it.
nilepez - Wednesday, November 19, 2008 - link
With all due respect, sites have been pushing large PSUs for years. As I posted earlier, people were trying to convince me I need 600w 3 or 4 years ago, when I built an Athlon 64 Rig with an X800XL: a rig that couldn't not possibly have used 300w, even when overclocked, from the wall, much less from the PSU.As for the idea of what you'll need down the road, by the time you need more PSU (esp due age), you could just buy a new quieter, more efficient PSU, with more bells and whistles of equal or higher quality with the money you saved.
Besides, in 20 years of computing, I've never had a PSU die. The worst thing that happened was a fan died. Bought a new fan and it worked like a champ, and that was some POS PSU that came with my Inwin Case (I think I still use that PSU, 10 years later!).
buying a quality PSU makes sense. Buying 750w+ PSUs only makes sense for someone running Tri or quad SLI, which means almost nobody. I've seen developers at work return 600W PSUs, because they feared that they'd need more to run to 8800GTs.
Those 2 cards pull at most 160w...add in a Core2 CPU, and you're looking a rig that is unlikely to pull 300W while playing far cry with Super Pi (just in case there's an idle cycle) running in the background.
It's almost all marketing hype.
Griswold - Friday, November 14, 2008 - link
I've been saying this since Chris' first (excellent!) review here at AT. I really wish he would push those insane power monsters with extra bling off his workbench and start reviewing those PSUs the majority actually buys.Christoph Katzer - Friday, November 14, 2008 - link
Next one up will be most probably the Thermaltake TR2 QFan series with 300, 350, 400, and 450W. Everyone cheer up! ;)