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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walk2k - Tuesday, November 18, 2008 - link
If you're curious to find out what your system actually uses, for about you can buy a P3 "Kill-a-Watt" power meter from Amazon for about $24. This is a doo-hicky that plugs into the power outlet, and then you plug whatever you want to measure into that. I've personally found it very enlightening.My current PC uses about 120 watts idle in XP, up to about 150 watts when actually doing stuff (cpu slightly loaded, HDD churning). Then in games with the GPU loaded it uses about 200 watts. I only managed to get it to 233 watts when running both a cpu stress test (Orthos) and GPU benchmark (3dmark06) at the same time.
I'm in CA and pay about 13 cents/Kilowatt/hour so theoretically if I left my system on 24/7 (I don't) at idle it would cost me about $11 per month. In reality I use my computer about 5 hours a day, with about half games (200 watts) and half just surfing, etc (120 watts) so say average 160 watts x 8 hours x $.13 x 30 days = $5 per month.
glynor - Tuesday, November 18, 2008 - link
The prices listed on the EIA website that you used to generate all these numbers (for the US) are based only on the price residential customers pay for energy generation, and do not include the cents per KWH charge that all customers must pay for transmission. Even though I simply take the standard offer from my utility company (like most people), my actual price is roughly DOUBLE what the EIA lists as the average for my state.Look at your bill. Make sure to add the totals for both Generation (Supply) and Transmission. These are billed separately.
With that in mind, most of the example totals reported in this article, and certainly all the comparisons to "Europeans paying more" are completely bogus!
Maiyr - Tuesday, November 18, 2008 - link
Why bother with all of this just to figure out how much it costs to run your system ? Surely someone must have thought of just plugging in a Kill-A-Watt Electricity Usage Monitor....Maiyr
gochichi - Tuesday, November 18, 2008 - link
I would look for better efficiency rating for the following reasons (in this order):1) I speculate the product is a higher quality product.
2) Inefficiencies turn into waste heat, cooler is more stable, more pleasant, and longer lasting (speculations)
3) I guess maybe saving a couple of bucks on my bill, but it's definitely not as important to me as just knowing that a have a "pimp" power supply.
What this article does make me want to do is try to figure out what sleep modes best suit my desktop computers (particularly my seldom used older desktop). Cold booting is inconvenient and I have been careless about finding a reliable sleep mode. I think the trick is to go S1, I just switched my main computer from S3 to S1 and it really helps stability and responsiveness.
I wonder how running laptops does in terms of power efficiency. There's got to be a ton of inefficiency caused by charging and discharging the batteries all the time. The design circling around a portable battery also makes it pretty power thrifty at the same time. Just curious as to how it actually pans out. Laptops have typically been more robust in sleep mode too though.
Random comment: Is it just me or have software updates gotten beyond the ridiculous point? Seems like they are not only often, but they are in your face... like it's OK to interrupt what you're up to a few times a week to get the update "right now"... I mean forcefully.
bob11d50 - Sunday, November 16, 2008 - link
I just wanted to justify my purchases of energy efficient computer components.The reason for this was about 3 years ago I had 9 people living in my house and the power company was on a teared system. I got up to the fourth tear where power was up to $0.85 KWH. This was in San Jose California with PG&E as the power company.
I got my server down to 77 WATS with a EE Athlon at idle from about 230 with my dual Opteron. All measurements were using the Kill-A-Watt.
sheh - Saturday, November 15, 2008 - link
I was always under the impression your total power readings were at the outlet, and so included the efficiency loss of the PSU. If that wasn't the case, how do you measure total power draw from within the computer?Christoph Katzer - Sunday, November 16, 2008 - link
Motherboard, system, graphics-reviews got readings from the wall. power supplies are loaded with a programmable load, so we can easily calculate the losses. You can know the power draw from mobos, gfx and so on when measuring the power distribution inside of the case which isn't difficult if you know which cable powers which part of which component ;)bigsnyder - Saturday, November 15, 2008 - link
What kind of case is that in the picture?Christoph Katzer - Sunday, November 16, 2008 - link
Silverstone TJ10GimpyOne - Saturday, November 15, 2008 - link
Not sure about Europe, but here in the US, the cost of "electricity" is only about half the bill. Once they tack on things like Fuel Cost charges, Energy improvement riders, resource adjustments, etc. you double the actual bill (literally).So more appropriate cost saving could actually be closer to 2x what is here.