For something that doesn't run continuously, like eg. a refrigerator, then an average daily usage is more useful, no? "This product draws 1.5 kW with a duty cycle of 0.08" doesn't really help when comparing efficiencies of potential purchases, you'd need to convert it to electricity consumed in a set period anyway.
this post was submitted on 15 Jan 2025
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No, it's because watts are joules per second, so kWh are (energy / time) * time. Cancelling the units would be expressing the energy directly in joules.
But the XKCD mentions kWh/day specifically, in theory the times can cancel out, leaving you with kW
But instantaneous and average kW are very different, and it would take more time to describe that distinction than to use kWh/day.
My freezer was labeled in max watts, kwh/day, and kwh/year. Because the cumulative watts over time is what I pay for my power bill. That way it's a simple multiplication that tells me how much having that freezer would cost.
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Exactly, it's a unit of convenience, not a unit of abstract precision.
Even a unit of "gallons/sqft" could be handy in the right context. If you were trying to design a storage solution for discretely packaged product for example, it could be a figure of merit despite literally factoring out to a unit of length.
I could imagine a scenario where gal/ft² is useful. Like with grocery store shelving figuring shelving and product stacking. If liquid storage containers are stackable then you have have more gallons per square footage of shelf space. Or of they're not stackable, then taller containers would hold more liquid in the same shelf space than shorter containers with the same footprint.
Yeah it seems odd to represent something as a volume/area, but that is the relevant information you're comparing and it's intuitive how that number changes based on changes to volume as projected onto an area. Bigger number points toward a more efficient use of shelving.
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Yeah a chest freezer is a good example of a situation where both are useful things to put on the tag
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You could also list some long term average power draw instead of the peak.
kWh is already an uncanceled unit, drives me nuts even without adding per day
(Energy / time) * time? fuck you
It's because the times aren't the same. Maybe same unit but different context so they can't be canceled.
It's like saying you work 8 Hours/day (Eight hours per day). Both are units of time, but their context is different and their combination forms a new meaning beyond the units.
1 KWh is using 1KW for one hour. Because of demand pricing the time you use that KW is important. Like in terms of energy grid using a whole ton of power for one minute vs same total over a long time is different and important dispite being the same amount of energy.
Edit: some phrasing
Time cancels out.
I work 8.
Gotta convert time to the same units before canceling: you work 1/3
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Good point, and agreed that thinking in kWh is very intuitive and convenient in some contexts like household appliances, but it's being used as a more general unit for energy while Joules are just so much better at, well, representing energy and being able to transition from electric to thermal etc.
I know why but it's stupid and arbitrary and the arbitraryness is what's forcing it.
It's the time. It's always the time.
SI units are all derived from seconds but instead of working with kiloseconds we have minutes and hours and days with a bunch of idiotic conversions.
The "second" you invite time into your measure, you invite some real bullshit ad-hoc pseudo-unit convenience units and fuck them. May as well just go imperial and have 14 rods to the fucking hogshead.
Is that a standard hog or a chefs hog?
Because nobody's used to seeing Joules, you could swap in kJ for kW-seconds but then you probably need to switch base (MJh) to keep it practical, and now people need to do extra math to tell what will be on their power bill
But go ahead and call your power company to get them to list Joules
My power company provides me electricity in kWh, and heating (in the form of hot water) in GJ. And my cold water gets charged in m3.
So they DO know. For a few years, they'd even "helpfully" translate the GJ into kWh, untill it started to piss off people who bought electric heaters and found that those two numbers weren't actually the same in the real world.
My power company DOES tell me in Joules, but only for gas so that's already bullshit, and I live in Alberta so people already can't decipher their fucking power bill's opaque energy/distribution fee/transmission fee costs so that's bullshit too
But ...we're human - bullshit is really all we've got.
I suppose there is science, but eww...
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It's also due to social inertia.
Power companies charge by the kWh because their generators are measured in total output wattage and consumers consume at different wattages at different times.
Sure, it would be easier to measure in total joules consumed per period time but it would also be easier to measure with world standard metric units. The pain of changing is harder than staying the same, so muh freedum units.
It gets even better when you read about annual or even daily energy production of a specific power plant.
For example, the annual production of Aswan dam in Egypt is about 10 042 GWh, which translates to an average power output of about 1.1 GW. Now that you have this number, you can compare that with the maximum theoretical power output which is 2.1 GW. Therefore, they should have plenty of capacity left, but you can't tell that just by looking at the published numbers. They just have to use convoluted units, because that's the tradition in a bunch of industries.
There's nothing wrong with kilowatts, it's an SI unit. The problem is hour, which is 3600 seconds, and we have ancient Egyptians to blame for this, who divided the day into 24 hours despite having already developed base-10 numerical system.
Kilowatt per kilosecond, which is 1 megajoule, would work better.
Damn, I was convinced it was the Babylonians with their base-60 system.
That actually works great.
60 is cleanly divisible by 1, 2, 3, 4, 5, and 6, 10, 12, 15, 20, and 30.
10 is cleanly divisible by 1, 2, and 5.
I have no problem remembering what 1 is divisible by.
It would've been better if we had a 6 or 12 based number system
The big reason for 60 over 12 or 6 is the divisibility by 5. That makes it divisible by all numbers through the first 3 primes.
To get it divisible by all the numbers up to the next prime (7), you'd have to go to 420, and the one after that (11) you'd need to go to 27,720, and 13 would require a whopping 360,360.
The problem with base 60 is needing to know and remember instinctively the names, symbols, and relative positioning for 60 digits. Like, I love Babylon, they're underrated for certain, but imagine teaching this to a 5 year old. Imagine doing calculus with this shit. Now remember that their writing impliment was a triangular reed and their written marks were entirely triangles and straight lines.
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Yeah Babylon was very clever but also looking at their math and writing makes it clear why they had to have a class of people to do their math and writing
I really don't get the issue with kWh. Things are rated in W and we mostly care about the hours they're powered on. If I wanna figure out how many kWh a PC that needs 300W used in 4 hours, I multiply 300*4. If I wanna know how many joules it used, I have to do 300*4*3600. Only one of those can be done in your head in 3 seconds.
You gotta use an escape character, specifically a backslash ( \ ), when dealing with *s on lemmy.
Otherwise you end up with "stufflike this!"
When it could have been "stuff*like this*!"
ETA: Damn, you're good. Fixed it before I even finished this post!
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My car needs 0.07 square millimeters of fuel on the highway.
Isn't that crazy efficient? I seem to remember about 0.3mm²?
Way back of you asked Google "38 mpg in mm^-2" it would tell you.
I love that it's the size of the thread of fuel you would consume as you drive down the road.
Edit: oh no, that's about right. It's a diameter of about 0.25 mm. I think that's what I was thinking of.
Not sure. I asked my cat Jeepity.
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I need the alt text!
Sorry! I added it now.
First of all, thanks for posting new threads here, it was getting somewhat dull that I was in recent weeks always the first one, sometimes after several days.
You might want to post comics the same way I did: https://discuss.tchncs.de/post/28278776 i.e. not just with the alt text, but also with a link to explainxkcd. You can easily copy the alt text if you switch to m.xkcd.com.
Going from Watts to BTU's while researching for a solid state multi-power-state TEC cooling solution. I feel this.
But what temperature is that at? And what is the ambient temperature? And what if the power is not at exactly 120V? And what about if I put a fresh dead hooker in it every day?
If we just used watts life would be so much easier.
The beauty of SI units is you just add or remove zeroes.
Unless you're converting seconds to minutes, hours, days, years, etc.
Then you get things like watt hours. Or light years.
Which is why neither are SI-units
The Hives were right, we need to convert to the metric system for time.
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And they're cursed for a region, you don't define a distance as volume! As I'm typing that, I realise this also defines a distance as a bodypart, ah well
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