this post was submitted on 15 Jan 2025
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I can't imagine why kWh would be more convenient than MJ though.
Because people have an intuitive feeling about how much 1 kW is, because they use devices with a power rating in Watt and have a feel for how powerful a device is at what rating. People also know exactly what an hour is. So it makes sense to think about a device of 1kW running for 1 hour, people have a good sense of how much energy that is in daily use. Since most energy bills are also in terms of kWh, people also have a good sense about the costs of that energy.
Given the popularity of the unit, I think people like it, otherwise a different unit would have been used already.
Yeah i haven't dealt with joules on a regular basis since college. They may as well be coulombs to my instinctive understanding
Right, so it's only the popularity of the unit. If everyone would use MJ that's what people would be used to and there'd be no real difference.
Because the power draw of appliances is measured in watts, so a 60 watt light bulb when lit draws 60 watts of power over the course of one hour. So if I have roughly 100 lightbulbs at 60 watts hooked up to my house, then I'll be using 6 kW of power each hour.
It tells us more information about the rate of use of that energy. It's like the difference between a 2 lb sphere of uranium being exploded in a fraction of a second vs 2 lb lf uranium fuel in a reactor operating for however long that much fuel lasts for. Both contain the same amount of joules of energy at the end of the process, one just uses all of those joules in one go and the other slowly releases that energy over a longer period of time.
kWh is just a measure of energy though. B it says nothing about the time in which it's expended. It's possible to use a kWh in a minute.
Glad to see reading comprehension is at an all time high and I definitely didn't explain how total joules doesn't actually mean anything for something drawing power in relation to the time its drawing power. And I didn't make any comparison about how a 2lb lump of uranium contains the same energy whether it's detonated in a bomb or slowly released in a reactor.
My point is that kWh is the same. It doesn't say anything about time. 1 kWh is 3.6 MJ. There is no difference except the factor 3.6.
The important thing is that leaving units uncanceled is a valid way to communicate the relevant factors of what a number represents.
Yes technically kWh cancels down to joules, but that doesn't communicate the relevant info of how a device uses that energy during a period of time. In other words Work (Watts) multiplied by Time (hours).
Uranium has 2x10¹³ joules of energy stored. You can use all that energy at once in a bomb and explode a city in a second, a lot of Work done very quickly, ooooor you could put it into a reactor and power a city and do a lot of Work during a much longer time period.
And the amount of kWh provided is the same in either case. So using kWh gives you no relevant information about how the device uses that energy during a period of time.
It definitely does provide information as my 50 watt lightbulb will run for an absurd number of years when hooked up to a nuclear generator and will be completely vaporized by the nuclear bomb.
Also keep in mind your average person likely doesn't remember their physics classes and how joules, time, and watts all relate to each other and that introducing new names to something just creates more confusion and headache and dumbasses phoning into their electric companies about how "my lightbulbs don't take joules they take watts and why am I paying for joules when I want watts."
kWh conveys the relevant information without introducing other names that can create confusion among the stupidest and most karen-like people you know.