Have you ever thought about how much it cost to run your PC -- the one you're using to read this article? What does it cost to play games, surf the Internet, or download files? It all costs money -- money that you, your parents, or whoever is in charge of the monthly electricity will have to pay. Those of you in charge of paying this bill will surely be interested in keeping costs down, which is why you might want to pay a little more attention to what sort of hardware you are using in your computer.

Many users -- especially computer enthusiasts -- put together a new PC that can easily handle any task, without much thought for power efficiency. If you intend to use the computer primarily for gaming, buying a high-end processor and graphics card makes sense. Likewise, if you intend to do complex three animations or movie encoding, you'll probably want to have as much processor power as possible. If all you're going to do is watch movies, run Microsoft Office, and surf the Internet, you're not going to put a big load on any of the components. In that case, your PC will typically be idle and waiting for user input, while any high-power components will still go merrily along sucking down extra power.

We recently looked at the topic of power consumption for each component in the PC. Of course the numbers were merely a rough estimate for our specific setup, programs, and tasks, so that article could serve as a baseline for the amount of power your system might require. We also discussed how power requirements affect the type of power supply that you will want to purchase. In this article, we want to focus more specifically on the costs of running a computer (not counting anything like broken components and upgrades). We look at electricity prices in the US and Europe to calculate how much various types of PCs actually cost to run. Perhaps you're one of those people with multiple systems -- one for gaming, one for office work, maybe one or two for the kids, and perhaps a few extras running distributed computing tasks 24/7. We will look at several different workloads to see how much various types of systems actually end up costing on a hourly, daily, and yearly basis.

KWh prices in the U.S and EU

When we started researching prices of electricity (measured in kilowatts hours/kWh) for the different countries, we were surprised by the huge differences in price. In the US prices range from $0.05 to $0.21, according to the Energy Information Administration -- the average price is $0.089 per kWh. European prices are different for each country, so we will just take Germany as an example. Prices there are high relative to the US but about average for Europe. In 2008, Germany has an average of 17 to 22 Cents (€) -- about $0.22 to $0.29 USD! That's anywhere from 1.5 to 6 times as expensive in the old world depending on where you live; obviously, areas where costs are higher will probably be more interested in PC power consumption, but that is a separate issue from what we are looking at today.

Calculating Power Requirements and Costs


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  • The0ne - Friday, November 14, 2008 - link

    I would have to agree. If only power requirements were more accurate or rather stated for general usage some of us wouldn't have to go out and buy these 700-1000W PS for a system that draws half of that.

    All in all though, I have to put things in perspective. I waste more time and thus money playing games on my PC; Heroes of M$M 3 and FFXI. So while I can save a little by turning off the PC once in a while and getting more efficient parts, I'll save even more if I just cancel my FFXI account :)
  • Mr Perfect - Friday, November 14, 2008 - link


    It's especially important to have reviews of reasonably size PSUs when you take a look at efficiency curves on PSUs. PSUs achieve their best efficiency at higher loads, which is why 80+ testing only requires 80% efficiency at 20%, 50% and 100% output to qualify. So a 80+ certified 1000watt PSU will be at least 80% efficient if you're pulling over 200Watts, but if your system draws less then that, efficiency can tumble down into the 70s or 60s without breaking any rules. On the other hand, if you have a 500 watt 80+ PSU, you'd have to draw less then 100watts before you get into the low end of the efficiency curve. For people with HTPCs or budget boxes that really do draw under 100watts, they'll probably want something even smaller, like 300watts.
  • Clauzii - Friday, November 14, 2008 - link

    Agree! Most systems use under 300W total, so a bit more of those would be nice. Reply
  • nilepez - Tuesday, November 18, 2008 - link

    I also agree. I have a Core2 CPU and GTX260, and at idle it's pulling around 120w from the wall. I don't recall what it was pulling at 100% CPU/GPU, but I believe it was roughly 220-240.

    A few years ago, I was talked into buying a 500W PSU, because I needed
    that to power a Athlon 64 and an X800XL.....of course it idled between 70-90w (from the wall) and never hit 200w....ever.

    I did replace it with another 500ish PSU, but in this case, I bought it because the Corsair is very quiet and has modular cables. Power wise, I would have been fine with a smaller psu.

  • mpjesse - Friday, November 14, 2008 - link

    This is a great article. What would be even cooler is if ya'll made some sort of web calculator that could compute the total cost of running your system based on a few known variables (CPU type, GPU type, # of hard drives, time spent idling, etc) and maybe even each U.S. state's electricity rate. That'd probably be a lot of work, but I'd certainly use it everytime I start a new build. Reply
  • Clauzii - Friday, November 14, 2008 - link

    You can try this:">
  • TennesseeTony - Friday, November 14, 2008 - link

    From what I've seen and read, my ancient power supply is at best 65% efficient. Judging by the many comments I've read here on this site, many many others are still using their ancient P4 3.06Ghz systems on a daily, often 24/7 situation, as well.

    I for one don't consider the efficiency rating to be marketing hype, and am very glad to see these better designs.

    Fortunately for me, I held off on the Conroe, saved my pennies, and next week (hopefully) I get to place the order for the final component in my new build...a Nehalem Core i7 920. (Got the Asus p6t ordered from last night.)

    Just a few more days and I get to fire up my new 85plus power supply...Woohoo! At idle, with the increased efficiency, perhaps my power costs will remain the same? I could pinch those pennies really tight and reus my old PS, but the new one will pay for itself in short order in my situation.
  • joseps75 - Sunday, November 1, 2009 - link

    My PSU for my 5 computers varies from 3 to 5 yrs old. Mostly I keepupgrading my MB AND CPU'S. Now all my 5 boxes are running quad cores processors. Since I runn them 16hrs daily, I hook up a KILL A WATT EZ to each box to check how much power each box consume. Here are my data for each box tagged by MB NAME: 1) #1 P5K-E $0.0164/HR, 2) #2 P5K-E, $0.0144/hr, 3) P5K-V, $0.0125/hr, 4) #4 P5Q-SE, $0.0156 and 5) #5 M3N78-VM, $0.0105.
    I use my computer hobby to run volunteer research on medical cure for human diseases at Rosetta@home and World Community Grid. They are worthy non profit research to find cure for human diseases HIV, AIDS, ALSHEIMER, CANCER ETC.
  • whatthehey - Friday, November 14, 2008 - link

    I don't think anyone is suggesting that a six year old power supply shouldn't be retired. I looked at the spreadsheet they gave on the last page - damn sweet, I must say! Anyway, I was poking around with some numbers to see what it says about lesser PSUs. If you have a 60-65% efficient PSU with your old system and the PC drew 125W to 250W (for the components, not at the wall), and you run it 8 hours per day with half the time at full load and half at idle, you can get a result for your savings per year.

    Assuming the spreadsheet is correct and I put things in the proper spot, you're looking at a yearly power savings of around $15 to $30 using the above scenario. If you run all the time, your savings would be anywhere from $40 to $100 per year. That's all going with equal power requirements and 60% idle/65% load efficiency to 84% idle/85% load efficiency. The new power supply might pay for itself in a year or two, but for power requirements your PC would take much longer to pay off. But then, more performance is its own reward, right?

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