Calculating cost to run PC 24/7

The1nonly1 · 15 Jul 2021 at 19:18

I think I have this correct but please correct my if I am wrong.

Let's say my PSU is under load and outputting 450 watts. Over a 24 hour period that would be 10.8 kW/h. My kW/h charge is £0.16 so would that mean it would cost me £1.73 every day to keep the PC running?

Over a week that would be £12.10 and over a year £630.

Have I worked this out correctly?

jaybee · 15 Jul 2021 at 19:22

Yes

450w = 0.45 kw/h
0.45kwh x £0.16 = £0.072 per hour
£0.072 x 24 hours = £1.73 per day
£1.73 x 30days = £51.84 per month
£1.73 x 365days = £630.72 per year

But why would it be under constant 450watt load unless you are mining with 2 or 3 cards or gaming constant. You can also turn it off over night etc.

watercooledman · 15 Jul 2021 at 19:24

average say new ryzen left on idle for the year with a little gaming ?

Tetras · 15 Jul 2021 at 19:31

You'd have to factor in the monitor and speakers too, plus UPS if you have one.

jaybee · 15 Jul 2021 at 19:36

watercooledman said:
average say new ryzen left on idle for the year with a little gaming ?

Just use the calcs above and instead of starting with 0.45kw/h and £0.16, change them to your average daily watts and your daily elec rate in kw/h. So say your rate is also £0.16 per kw/h (check your bill) then lets say you game for 3 hours a day on average at 400w. The rest of the day all day it idles at around 50watt for the entire system. That would come out at something like £130 per year.

As above, you have to consider other things. Depends to what level you want to go to. Lights on in the room/heating? Monitor/speakers/UPS etc etc. Monitor can use anything from 30 to 150watts depending on model.

The1nonly1 · 15 Jul 2021 at 19:48

Thanks all. It wont be running 450 watts all the time, that was just a figure I was using to get an extreme example.

Quartz · 15 Jul 2021 at 19:51

The1nonly1 said:
Let's say my PSU is under load and outputting 450 watts.

You need to look at how much power is going into the PSU, not how much is coming out of it. Let's say your PSU is 80% (random figure) efficient at 450W, so you're actually using 450 / 0.8 = 562.5W and that will cost you £787.50 per year

jaybee · 15 Jul 2021 at 20:07

Basically just buy a "kill a watt" meter type device or a modern day smart plug which includes energy consumption readings. Monitor the usage that way to get actual readings.

The1nonly1 · 15 Jul 2021 at 21:12

Quartz said:
You need to look at how much power is going into the PSU, not how much is coming out of it. Let's say your PSU is 80% (random figure) efficient at 450W, so you're actually using 450 / 0.8 = 562.5W and that will cost you £787.50 per year

Thanks, I wasn't aware of this.

jaybee said:
Basically just buy a "kill a watt" meter type device or a modern day smart plug which includes energy consumption readings. Monitor the usage that way to get actual readings.

Yes, I have seen these and will get on thanks.

davey_g10 · 15 Jul 2021 at 22:55

Quartz said:
You need to look at how much power is going into the PSU, not how much is coming out of it. Let's say your PSU is 80% (random figure) efficient at 450W, so you're actually using 450 / 0.8 = 562.5W and that will cost you £787.50 per year

Just to clarify what you man here, so does that mean whether using intensely or not, if the machine is on 24/7 it would cost 787.5 for the year to run? Or did I misinterpret?

gpuerrilla · 15 Jul 2021 at 23:03

He means the figure you measure from the computer will be the energy it consumes at component level (with software). If you measure before the PSU converts the power to the low voltages, your actual consumption is slightly higher at your wall socket. All supply units are not 100% efficient, some energy is lost, so if you have a budget one that's likely bronze and then you have load levels to consider.

Quartz · 15 Jul 2021 at 23:05

Precisely.

davey_g10 · 16 Jul 2021 at 15:45

Thanks, I understand that distinction. So am I therefore right in thinking that it doesn't matter what you're using the machine for, whether running at high usage or not, as it will just convert to the voltages it needs to meet demand? So if it's on 24/7 it will use the same cost per year regardless of how you're using the machine? Or am I misunderstanding that and the intensity of usage still matters?

Zefan · 16 Jul 2021 at 15:51

Intensity of usage 100% still matters. He's simply explaining that because PSUs aren't 100% efficient that the system's own measurements of power consumption will be out by whatever the efficiency % is.

dave28 · 16 Jul 2021 at 16:05

Yes but not many would do that unless there was a specific reason.

Thats a big bill to run 1 PC

Tetras · 16 Jul 2021 at 16:11

davey_g10 said:
Thanks, I understand that distinction. So am I therefore right in thinking that it doesn't matter what you're using the machine for, whether running at high usage or not, as it will just convert to the voltages it needs to meet demand? So if it's on 24/7 it will use the same cost per year regardless of how you're using the machine? Or am I misunderstanding that and the intensity of usage still matters?

Intensity of usage and the amount of power being demanded from the PSU is a direct relationship. High intensity = high power draw.

The PSU is usually more efficient with high load, but you wouldn't deliberately do things just to push the PSU into an efficient state.

rumple9 · 16 Jul 2021 at 22:20

I received a smart meter from my energy supplier last December and I was shocked to see how much my PC uses when gaming, but yes around £1.73 a day is about right. Double it if you get a 3080+

gpuerrilla · 16 Jul 2021 at 23:20

rumple9 said:
I received a smart meter from my energy supplier last December and I was shocked to see how much my PC uses when gaming, but yes around £1.73 a day is about right. Double it if you get a 3080+

An undervolt and some tweaks to the settings in games should make that somewhat better!

Donnie Fisher · 18 Jul 2021 at 09:07

davey_g10 said:
Thanks, I understand that distinction. So am I therefore right in thinking that it doesn't matter what you're using the machine for, whether running at high usage or not, as it will just convert to the voltages it needs to meet demand? So if it's on 24/7 it will use the same cost per year regardless of how you're using the machine? Or am I misunderstanding that and the intensity of usage still matters?

You’re misunderstanding it. Imagine the usage being more like a car where the fuel used is the same as the Pcs power usage. Drive the car gently and it’ll use less fuel. Drive it hard and it use more. Same with the pC. Light use draw low power from the wall. Hard use mean something more power use from the wall.

The PSU will adapt to the demand placed on it, the same way a car adapts ten amount of fuel to the engine based on demand.

As a very very very rough estimate, for 24/7 usage, 1watt equals £1 per year.