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0 pointsgrues-dinner6mo ago0 comments

I dunno, 1kWh seems quite natural as a unit of building-scale energy usage when you know a kettle or space heater is about 3kW. We think about energy usage much more in terms of kW and hours than in watts and seconds. And even in small devices like an LED bulb, 5W is more obviously 0.005kW than, say, 2 hours is 7200 seconds.

And in this context it's much more obvious that it can notionally deliver energy at a peak rate of about 1% capacity per hour. If you said 1MW/360GJ, I don't think that would be nearly as clear.

Same for batteries, which started with car batteries/deep cycle batteries, rather than AA batteries, which usual don't even say, and phones. A battery that provides 1 amp (at 12V, but that's already given in a system) for 50 hours. Makes immediate practical sense, especially when equipment is often labelled in current draw and you can measure amps with an ammeter. 2.16MJ far less so.

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flowerthoughts6mo ago

This still falls under the "but we're used to it" argument. That notion that it feels natural, I argue, is a result of you having seen both W and Wh in enough contexts that you start building intuition for them. Had we had W and J, you would have been able to build the same intuition.

> If you said 1MW/360GJ, I don't think that would be nearly as clear.

Wouldn't have been using the hour as the mental reference. As you say, it's impractical. We would have probably rounded the 86,400 seconds in a day to 100,000 and used that as the reference for comparisons. There's nothing noteworthy about the hour in this context.

> A battery that provides 1 amp (at 12V, but that's already given in a system) for 50 hours. Makes immediate practical sense, especially when equipment is often labelled in current draw and you can measure amps with an ammeter. 2.16MJ far less so.

I argued Ah could have used the SI base unit C, not that we'd use J. Whether you count As or Ah is still just a matter of building intuition.

Gud6mo ago

Absolutely agree.

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