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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7Enigma - Monday, November 17, 2008 - link
I think you mean 1/2. Most of these charges are regardless of actual power used. Things like transmission charges, local/state taxes, "improvement" fees all will be the same each month whether you draw 100kW or 10. Where the savings *can* become more than stated is if your local utility uses a stepped price plan. That is to say you pay $X up to 500kWh's, then a higher rate after that level. This is how my bill is done unfortunately. I was under the impression there was some sort of peak hour price and another price for off-peak (as many places have). This can be taken advantage of by doing high energy tasks like the washer/dryer/dishwasher/ect. at night or early in the morning where you may be paying anywhere from 20-50% less for the same amount of power. With flat rate stepped plan you cannot benefit from using off-peak, and in general wind up paying more for your energy since they don't care if you used that 1000wh at 3am or 5pm.Everyone should check their bill statement and look to see how they are being charged. If you have a stepped plan like mine you may benefit more from being more energy conscious than if you have typical peak/off-peak pricing.
raWill - Saturday, November 15, 2008 - link
Infact I have thought about it - I'm so glad I got rid of my 8800GTS, what a pointless consumer of power when all I do is surf the net 90% of the my computer is on.Even worse is people that leave thier sli systems on whilst downloading torrents, etc.
By managing my standby power sources (turning them off every night before bed) and only downloading torrents and such whilst I am using the computer I saved about $20 a month in electricity. I live on my own too!
mongo lloyd - Friday, November 14, 2008 - link
PSU efficiency will always be higher in Europe than the US due to 240VAC. I didn't see you adjusting for this, but granted, I only skimmed the article because my electricity bill is baked into my rent.ggordonliddy - Friday, November 14, 2008 - link
It's okay, Osama will pay for it. I mean Hussein. I mean Obama.atm - Friday, November 14, 2008 - link
Thanks for posting this article. Without the monitoring equipment at home, I was in the dark about true system power draw.ytsejam02 - Friday, November 14, 2008 - link
I am all for saving energy. I have 3 computers in my house (laptop, desktop, and htpc), and both the htpc and desktop are running 45W cpu's with the Western Digital Green Power drives, and using the onboard graphics and sound. I run all the programs I need with that, so I hope I'm doing something right with these configurations, and that they are low power consumption.Now my problem. How much energy would be required to recycle a constant PSU turnover? I'm sure it wouldn't be constant, but I've no idea what it would cost, so I'm thinking in generalities at the moment.
Either way, I'm guessing that would eat into a large part of the overall global energy problem.
IcePickFreak - Friday, November 14, 2008 - link
I'm waiting for PC Power & Cooling to release their 10MW fusion reactor PSU. No longer will I be tethered to a power outlet or subjected to power outages.As a bonus, think of the m4D 9AM1nG 5ki11z I'll have when I sprout a third arm!
Carnildo - Monday, November 17, 2008 - link
I'm afraid you'll be disappointed, then. Fusion reactors don't cause mutations.chenedwa - Friday, November 14, 2008 - link
Could anyone estimate the cost of a typical laptop setup? Many will keep the laptop's adapter plugged-in 24/7 regardless of whether the computer is attached.strikeback03 - Friday, November 14, 2008 - link
Using a Kill-A-Watt for measurement, my T43 with 15" S-IPS screen, Pentium M 1.86, ATi X300 graphics, 2GB RAM, and 100GB 7200RPM HDD uses 11W at idle with the lid closed, 18-21W at idle with the screen on (depending on brightness) and about 40W under load. Other laptop reviews on the site here offer power consumption numbers as well.