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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bob4432 - Tuesday, November 18, 2008 - link
exactly, and if you are not afraid of flashing your video bios, then you can really tweak the power setups for the lower end power "2d" mode to much less than what ati put in as a default. i think ati rushed the 4850 and sounds like 4870 bios when they first came out (extreme heat, lack of real power savings, etc) but hopefully now all that is fixed.fwiw - i do consider the amount of $$$ in cooling when getting a real measure on how much it cost to run the pc. i am in phx, az and ac is a must, so in my computer room/office it usually gets about 5-8F warmer than the rest of the condo and therefore that difference needs to be taken into account.
BitBodger - Friday, November 14, 2008 - link
One thing not considered here is the effect of the heat from the computer. That computer sitting beside your desk is also an electric heater constantly warming your home. Live in a cold climate and this is not entirely a bad thing since it takes some of the load from your main heating system. But if you live in a hot climate and depend on air conditioning don't forget that the heater never stops meaning that your AC works that much harder and consumes that much more energy getting rid of the extra heat. And given the inefficiency of AC technology, it costs more watts in the cooling process than are emitted by the heater.Hammarby - Friday, November 14, 2008 - link
In all these calculations shouldn't you also factor in how much extra it will cost to cool your house when you have a 100-500 watt space heater running for 8 hours/day??Christoph Katzer - Friday, November 14, 2008 - link
That's why the article calls "The Cost of Running Your PC"........Lifted - Saturday, November 15, 2008 - link
If "running your PC" increases the demand on your home cooling, then that is a cost directly resulting from running your PC. It is out of the scope of the article since there are too many variables to consider than just the cost of electricity.JarredWalton - Saturday, November 15, 2008 - link
But if it's cold and running your PC reduces the amount of time you run your heater, then running your PC would cost less in the winter. Besides which, plenty of people don't have AC, so even in the summer there's no added expense. Thus, we chose to limit the discussion specifically to how much your PC costs to run, and how PSU efficiency can play a role in those costs.7Enigma - Monday, November 17, 2008 - link
While electricity is 100% efficient (or near enough that we don't need to quibble), it is also true that very few people use it to heat their homes due to $/BTU. Until there comes a time when it is as cheap or cheaper to heat your home electrically I don't think your comment holds true.I also agree with the original poster that while not exactly in the scope of the article it is closely related and should have been mentioned. The common position of why spend more money on a more efficient PSU or any other component when the electricity costs show a ROI much greater than the usable life of that product is not accurate when cooling costs are not taken into account. While heating electrically is near 100% efficient, cooling is definitely not.
nilepez - Wednesday, November 19, 2008 - link
Lots of houses are heated with electricity. I've never lived in an Apartment with anything but electric Heat.Nevertheless, the heat from a PSU is negligible in the winter (even in the south) and an efficient PSU, by definition, produces less heat, which is especially true when the PC is idle.
ZoZo - Friday, November 14, 2008 - link
Or you can factor in how much less it costs to heat your home when you have a 150W space heater running for 8h/day.Staples - Friday, November 14, 2008 - link
I have not even read the article yet but I am surprised that was not even mentioned. That often adds 50% more to the cost if you live in a hot climate. Same thing with light bulbs. There is a double savings with CF bulbs.