[Guide] The Importance of Efficiency (or "The Cost of TDP")

vanished · August 23, 2019

In this guide I'll be looking into the often overlooked "hidden" costs of a high power consumption component by comparing what it takes to run it against something of lesser consumption that is otherwise identical in every way. This may be ironic coming from someone with a 350 W R9 Fury, but on the other hand perhaps that makes me more qualified than most to speak about it

I will be looking at three main categories, individually so you can ignore any that do not apply to you: cost of electricity, cost of a more powerful PSU, and cost of a more powerful cooler.

I will be comparing a hypothetical 250 W component against a hypothetical 150 W component, for a difference of 100 W. These can be anything - CPU, GPU, etc. - all that matters is the difference in power consumption and heat output.

Finally, before getting into it, remember that TDP, as stated on the package, does not necessarily equate to power consumption at all. Every company has a different way of rating it, and different loads will work your hardware to different degrees. For example, Intel states the TDP for their chips at the base clock, so even with no overclocking, you will exceed that number due to turbo boost behaviour.

Electricity

For those who have seen my guide on whether or not it's worth getting or upgrading to a higher efficiency PSU, you will be familiar with the following calculations. For the rest of you, go check it out

Assumptions and variables: (change any of these and recalculate if your situation differs significantly)

PSU Efficiency: 85%
Usage: 4 hours per day, 5 days a week, 52 weeks per year, totalling 1040 hours per year
Electricity cost: $0.12 per kWh
Difference in load: 100 W, as stated in the intro

Yearly cost: (100 W / 0.85) x (1040 h) x (0.12 $/kWh) x (0.001 kWh/Wh) = $14.68

This is not all that much, but it may still add up to a meaningful amount in 2 or 3 years, particularly if there is no other meaningful difference between the products you are considering. This is especially true if you use your system more, and/or pay a lot more for electricity. Consider this recalculation:

PSU Efficiency: 85%
Usage: 24 hours per day, 7 days a week, 52 weeks per year, totalling 8736 hours per year
Electricity cost: $0.18 per kWh
Difference in load: 100 W, as stated in the intro

Yearly cost: (100 W / 0.85) x (8736h) x (0.18 $/kWh) x (0.001 kWh/Wh) = $185.00

That's a lot of money! Granted, this isn't the situation most people will be in, but if you run something like 3D renders, folding@home, or other intensive tasks around the clock, it may not be far off the mark.

Power Supply

If your system consumes more power, you will want a more powerful PSU. So what does it cost to bump up to a 100 W larger version of any given model? I had a look through the offerings of a local retailer and found a range of offerings. Note that I used the MSRP, not including any mail-in rebates, sales, or other promotions. This was due to the fact they could potentially skew the results significantly. More on this later.

I looked at units from 450 W up to ~1000 W - above this things get a little crazy and that's not most people's segment anyway. I found that the difference between a, say, 550 W unit and a 650 W unit of the same model (EVGA G3, Corsair CX, etc.) ranged from about $5 to $50, with the most common numbers being $10 to $20.

As for why I didn't consider sales, it's because of things like this:

A good sale on a superior unit could make it match or even less than the cost of the cheaper one, rendering this consideration pointless. On the flip side, a good sale on the lower end unit could make the cost of upgrading due to the need of a high power draw part even greater, nearing the $50 end of that aforementioned scale.

Cooler

This is something that applies more to CPUs than GPUs since you have the flexibility of using whatever you like on a CPU, but GPUs generally come as a complete package, cooler included, and removing it is not something you do unless you are making a custom water loop build. For that reason, it's hard if not impossible to look at the impact of the cooler on cost for a GPU, but for CPUs it's much easier. A typical high-end cooler is going to run you somewhere around $100, whether it's air or water, and a more budget-oriented offering would likely come in somewhere from $25 to $50. Of course it's also important to consider whether the products in question come with their own coolers, and if they're good enough that you would use them, or if they're just a waste of money needlessly baked into the purchase price.

Conclusion

If it hasn't become obvious already, the impact really depends on your unique situation. If the more power-hungry product comes with a good cooler and the other one does not, you get a great deal on a higher performance PSU, and you are not paying for electricity, or just don't use your PC much, the difference may be nothing at all. However, if you're going to save $30 a year on power for 3 years, $15 on a PSU and $40 on a cooler, that's $145 you could instead invest in getting a higher end product from the more efficient line, or just keep in your pocket.

I hope this was useful, and if you see any mistakes or things you'd like to see added, please let me know down below!

Crunchy Dragon · August 23, 2019

8 minutes ago, Ryan_Vickers said:

if you see any mistakes

I think you spent way too much time on this, my friend

Also, a mandatory The More You Know.

This is pretty interesting, in all seriousness. I went from a 250W GPU to a 150W GPU, and almost survived with better power efficiency except I made up for my GPU's lost power in my CPU's TDP

PianoPlayer88Key · September 18, 2019

So if your electricity is upwards of ~30 to ~67+ ¢/kWh....

That was one of the factors that had me getting a GTX 1060 instead of an RX 480 almost a few years ago.

(Maybe I should ditch the GPU though, and just run the Intel HD4600, with the host i7-4790K underclocked to multiplier 8, 1 core, HT off, BCLK 90, adaptive voltage -0.25v or whatever is still stable in non-Prime95 loads, and RAM (have 4x8GB G.Skill Ares DDR3-1600 CL9 but remove 3 sticks) at DDR3-800, CL24... (Uh oh, the 30-40 or so HDDs...) )

vanished · September 20, 2019

On 9/18/2019 at 1:38 PM, PianoPlayer88Key said:

So if your electricity is upwards of ~30 to ~67+ ¢/kWh....

Wow that's crazy, best stick with raspberry pi I guess

Quote

That was one of the factors that had me getting a GTX 1060 instead of an RX 480 almost a few years ago.

(Maybe I should ditch the GPU though, and just run the Intel HD4600, with the host i7-4790K underclocked to multiplier 8, 1 core, HT off, BCLK 90, adaptive voltage -0.25v or whatever is still stable in non-Prime95 loads, and RAM (have 4x8GB G.Skill Ares DDR3-1600 CL9 but remove 3 sticks) at DDR3-800, CL24... (Uh oh, the 30-40 or so HDDs...) )

More seriously, I think the best combo right now is Ryzen + RTX, but I simply can't recommend RTX due to the terrible value, and, while I haven't looked super closely into it, I think the new AMD cards might actually be decently close now in efficiency (finally)