The Cost of Running Your PC
by Christoph Katzer on November 14, 2008 3:00 AM EST- Posted in
- Cases/Cooling/PSUs
Using a Higher Efficiency PSU to Reduce Costs
These days manufacturers are all promoting their high efficiency power supplies, and we have organizations and certifications like 80 Plus encouraging even small boosts in efficiency. Not surprisingly, plenty of users have been sucked in by the marketing and are now convinced that they need to purchase a new power supply in order to save money each year. Does it really make that much of a difference? The answer as usual depends on how you use your system. The previous page provided a baseline measurement, but now let's look at how much money you can save if you go out and purchase a new 80 Plus Bronze or Silver certified power supply as an upgrade to a slightly older ~80% efficiency PSU.
Our sample power supplies on the previous page are all relatively high-end choices for the specific market. Many (most) systems don't have power supplies anywhere near that nice, relatively speaking. So what happens when we switch to an older ATX 1.3 PSU -- something that would have been more or less state-of-the-art three years ago? Will a newer power supply really help you save the planet? Will it at least reduce your power costs and save you money? Let's find out, this time looking at power costs over the course of a full year: 24 hours a day, seven days a week.
For reference, we looked at some PSU efficiency results stashed away in our files and estimated ATX1.3 PSU efficiency at 75% idle and 78% load. That represents a high-end ATX1.3 PSU, and in some cases the discussion is hypothetical as it wouldn't be possible to find an older PSU with the necessary output rating. (That applies specifically to the high-end system.)
| System 1 24/7 Yearly Costs ATX1.3 versus ATX2.2 |
||||||
| Outlet Power ATX v2.2 |
Outlet Power ATX v1.3 |
Wattage Difference |
Savings NC | Savings CA | Savings GER | |
| Idle | 110 | 120 | 10 | $6.57 | $11.21 | €19.27 ($25.05) |
| Load | 167 | 179 | 12 | $7.88 | $13.46 | €23.13 ($30.06) |
| System 2 24/7 Yearly Costs ATX1.3 versus ATX2.2 |
||||||
| Outlet Power ATX v2.2 |
Outlet Power ATX v1.3 |
Wattage Difference |
Savings NC | Savings CA | Savings GER | |
| Idle | 190 | 213 | 23 | $15.11 | $25.79 | €44.33 ($57.62) |
| Load | 412 | 449 | 37 | $24.31 | $41.49 | €71.31 ($92.70) |
| System 3 24/7 Yearly Costs ATX1.3 versus ATX2.2 |
||||||
| Outlet Power ATX v2.2 |
Outlet Power ATX v1.3 |
Wattage Difference |
Savings NC | Savings CA | Savings GER | |
| Idle | 369 | 413 | 44 | $28.91 | $49.34 | €84.80 ($110.24) |
| Load | 663 | 705 | 42 | $27.59 | $47.09 | €80.94 ($105.23) |
Now we can see exactly how much money you might save during the course of a year by purchasing a new high efficiency power supply. Obviously, the more power your computer uses, the better your monetary savings. Looking at these tables, you might begin to think there's actually a point in upgrading power supplies -- and there is, provided you're running your computer a large portion of the time.
What happens if we change our usage model to something more realistic for most families? Instead of looking at 24/7 usage, let's change it to three hours of use per day on average, with two hours at idle and one hour at load.
| Yearly Power Savings for 3 Hrs/Day | |||
| Savings NC | Savings CA | Savings GER | |
| System 1 | $0.88 | $1.50 | €2.57 ($3.34) |
| System 2 | $2.27 | $3.88 | €6.66 ($8.66) |
| System 3 | $3.56 | $6.07 | €10.44 ($13.57) |
The need to upgrade power supplies suddenly doesn't seem as dire once we switch to a more realistic usage model. Particularly on low-end systems that only use 100W of power give or take, even an extremely inefficient PSU probably doesn't matter too much if the system isn't on more than a few hours per day. Even with power costs that are up to three times higher in some parts of Europe compared to areas in the US, the savings don't make sense.
If you happen to be the type of user that leaves your system on all the time, certainly you can save a fair amount of money by purchasing a better power supply. An easier solution would simply be to turn off your computer when it's not in use, unless you have a really good reason to leave it running overnight. Similarly, if your current PSU happens to fail, it might be worthwhile to spend a little bit more money to get a higher efficiency, better quality power supply. If you figure on a moderate amount of use and a five-year lifespan, you might want to spend as much as $50-$100 extra. Otherwise, there's very little incentive to go out and spend $150 on a top quality power supply just so you can save $10-$15 per year (or less).
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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.