3 ms·

Can you elaborate? Some of us flunked out of EE.

IshKebab 2y ago
It's kWh. Kilowatts multiplied by hours, not kilowatts per hour. The analogy with units you are familiar with: watts=speed (e.g. knots), energy=distance (e.g. (nautical) miles). So a kWh of energy is kind of like saying a knot-hour. Or 1 knot for 1 hour, which equals 1 nautical mile. You can say "I have travelled a distance of 1 knot-hour or 1 knot for an hour". It doesn't make any sense to say "I have travelled a distance of 1 knot/hour or 1 knot per hour". Knot/hour would be a unit of acceleration not distance. Ok that's probably clear as mud. I also feel like I should make a power units quiz website because so many people get this wrong.
- margalabargala 2y ago
  OP was not trying to say kWh. They were trying to say kWh per hour.
  - ErikBjare 2y ago
    1 kWh per hour is 1 kW
    - margalabargala 2y ago
      Mathematically yes, but linguistically no. One kWh per hour is the average production of the system. Calling a power generation system "1 kW" implies it maxes out at 1kW. For something like wind or solar which is usually at partial load, a 1kW system will usually not produce 1kWh per hour. Thus it is appropriate to say "1 kWh per hour" because you will need a ~3kW system to achieve that.
      - IshKebab 2y ago
        "1kW average"
        margalabargala 2y ago
        Yes that would also work. IMO "kWh per hour" is clearer, because when dealing with power generation those are the units you deal with when you are connected to the grid. When people talk about their solar generation, they say "I generated X kWh today", not "today my system averaged Y kW over Z hours" and leave the math to the listener. kWh per unit time is common when talking about home energy generation.
        hollerith 2y ago
        I hope you are trolling and not serious.
        margalabargala 2y ago
        I'm not. Why would you hope that? Sort of an unkind think to say. Would you like to elaborate on why you disagree so strongly?
        hollerith 2y ago
        >Sort of an unkind thing to say I will do better from now on. OK, first, let me say that I have no objection to your "I generated X kWh today". Neither do I have any strong objection to "kWh per day" or "kWh per month". But I do object to "kWh per hour". I would have the same objection to, "0.6 light-years per year". I would ask people to say, "0.6 times the speed of light" instead. It is common to need to refer to two different things that happen to have the same "dimension" (electrical power being an example of a dimension and energy being a different dimension). For example, a supermarket needs to distinguish "gross revenue", i.e., how much money it collected by selling things, from "net revenue", which is how much money is left over after subtracting the cost of the supermarket's having bought the things it sold. Note that both gross revenue and net revenue are best measured in dollars (if the market is located in the US). So according to you, if I understand correctly, you think it would be an okay idea for accountants to adopt the convention of using "dollars" as the unit when talking about gross revenue and "dollar-months per month" to signify that we are talking about net revenue. But what are you going to do when we need a third measure that happens to also be denominated in dollars (profit, say)? Are you going to adopt the convention that "dollar-miles per mile" refers to a profit measure? There was a famous physicist (Steven Weinberg, I think) who criticized Windows for giving science and technology a bad reputation. In particular, he worried that young people would react to the buggy behavior of Windows by becoming sour on the whole edifice of science and technology and would try less hard to learn science. I guess my main objection to "dollar-months per month" and to "kWh per hour" is like that: I worry that it will prevent (via confusion) some fraction of people from learning enough about accounting and the fundamentals of electricity to wield words like "gross revenue", "net revenue", "energy" and "electrical power" effectively. (One of the sources of my worry is my imagining how I personally would've reacted to coming across "kWh per hour" long ago before I had mastered the concepts of watts, energy and power.) To bring this back to where we began, if there are two different quantities of interest, namely, the advertised "capacity" of the panel versus the power a consumer can realistically expect to get out of the panel on a typical day, I would ask that people settle on some short phrases for both -- similar to "gross revenue" and "net revenue" -- and to denominate both quantities in kW (or kWh per month maybe).
- quectophoton 2y ago
  > because so many people get this wrong. All these terms are just so unintuitive for a mere mortal like me. Energy? Power? The difference between those two words has as much importance to the common person as the difference between "empathy" vs "compassion", or "theory" vs "hypothesis", or "less" vs "fewer". kW being a "stuff over time", but kWh being "amount of stuff"? I don't doubt the math checks out if you expand all units, but I'm as dumb as a wet rock so it took me a while to get this. --- If people wanted me to understand this way sooner, they should have started asking me to think in terms of "kcal" (kilocalories). At least I know that kcal is an "amount of stuff" because it's something you hear if you talk about food. And there's no mention of "hour" anywhere in the name (like with "kWh"), so the name doesn't have anything misleading. Then just tell me that "860.421kcal/h = 1kW" (the numbers don't really matter), and ask me to solve for kcal. When I move the "h" from the left to the right, and the equation becomes "860.421kcal = 1kW * h", everything will click. --- Food has kcal, so kcal is something that can be stored. When the equation has "kcal" on the left, it has "kW * h" on the right, so that means batteries store "kW * h". When I think of "kW" alone, I will remember that the "* h" moved to the left side and became "/h". I might forget stuff, but I know what food is, and I know that there exists an equation, at one side there's "kcal", at the other side there's "kW", and there's an "h" somewhere in there. And "kcal * h" will look wrong af, so I will remember that if the "h" at the left side, it will be "kcal/h". Result: Now I have an intuition for this. (EDIT: Escaping, and add some separators to hopefully make the comment easier to read.)
  - IshKebab 2y ago
    > All these terms are just so unintuitive for a mere mortal like me. Energy? Power? Yeah in fairness I think most people never have to deal with these units and they're used interchangeably colloquially. kW = power. This is a rate of work. How quickly work is happening. Intuitively, cycling hard = high power, cycling with low effort = low power. kWh = energy. 1 kWh is literally 1kW for an hour. If you are cycling pretty hard with a power of 0.1 kW for 10 hours, you have generated 1 kWh (0.1 * 10). If you cycle inhumanly hard (0.2 kW) for 3 hours you have generated 0.6 kWh (0.2 * 3). That's it. Now some examples: * Solar panel peak power. This is the maximum power output of the solar panels. For cycling it would be the hardest you can possibly cycle. Apparently the record for cycling is 2.7 kW! (But not for very long; unlike solar panels people get tired.) * Battery capacity. This is in kWh. They store a finite amount of energy. If you have a battery containing 10 kWh you can eek it out slowly - if you only draw 0.1kW from it it will last 100 hours. Or you can dump all the energy in half an hour and it will output 20 kW. The only really complicated one is battery factory output capacity, which approximately 0% of journalists understand. This is measured in Watts... because if you produce 1kWh batteries, and you make one per hour... 1kWh/ 1h is 1 kW! In other words if the batteries from the factory magically came out fully charged and you just used them as a power station without recharging them, then how much power could that power station provide? Yeah that one is a bit confusing.

It's kWh. Kilowatts multiplied by hours, not kilowatts per hour. The analogy with units you are familiar with: watts=speed (e.g. knots), energy=distance (e.g. (nautical) miles). So a kWh of energy is kind of like saying a knot-hour. Or 1 knot for 1 hour, which equals 1 nautical mile. You can say "I have travelled a distance of 1 knot-hour or 1 knot for an hour". It doesn't make any sense to say "I have travelled a distance of 1 knot/hour or 1 knot per hour". Knot/hour would be a unit of acceleration not distance. Ok that's probably clear as mud. I also feel like I should make a power units quiz website because so many people get this wrong.

margalabargala 2y ago
OP was not trying to say kWh. They were trying to say kWh per hour.
- ErikBjare 2y ago
  1 kWh per hour is 1 kW
  - margalabargala 2y ago
    Mathematically yes, but linguistically no. One kWh per hour is the average production of the system. Calling a power generation system "1 kW" implies it maxes out at 1kW. For something like wind or solar which is usually at partial load, a 1kW system will usually not produce 1kWh per hour. Thus it is appropriate to say "1 kWh per hour" because you will need a ~3kW system to achieve that.
    - IshKebab 2y ago
      "1kW average"
      - margalabargala 2y ago
        Yes that would also work. IMO "kWh per hour" is clearer, because when dealing with power generation those are the units you deal with when you are connected to the grid. When people talk about their solar generation, they say "I generated X kWh today", not "today my system averaged Y kW over Z hours" and leave the math to the listener. kWh per unit time is common when talking about home energy generation.
        hollerith 2y ago
        I hope you are trolling and not serious.
        margalabargala 2y ago
        I'm not. Why would you hope that? Sort of an unkind think to say. Would you like to elaborate on why you disagree so strongly?
        hollerith 2y ago
        >Sort of an unkind thing to say I will do better from now on. OK, first, let me say that I have no objection to your "I generated X kWh today". Neither do I have any strong objection to "kWh per day" or "kWh per month". But I do object to "kWh per hour". I would have the same objection to, "0.6 light-years per year". I would ask people to say, "0.6 times the speed of light" instead. It is common to need to refer to two different things that happen to have the same "dimension" (electrical power being an example of a dimension and energy being a different dimension). For example, a supermarket needs to distinguish "gross revenue", i.e., how much money it collected by selling things, from "net revenue", which is how much money is left over after subtracting the cost of the supermarket's having bought the things it sold. Note that both gross revenue and net revenue are best measured in dollars (if the market is located in the US). So according to you, if I understand correctly, you think it would be an okay idea for accountants to adopt the convention of using "dollars" as the unit when talking about gross revenue and "dollar-months per month" to signify that we are talking about net revenue. But what are you going to do when we need a third measure that happens to also be denominated in dollars (profit, say)? Are you going to adopt the convention that "dollar-miles per mile" refers to a profit measure? There was a famous physicist (Steven Weinberg, I think) who criticized Windows for giving science and technology a bad reputation. In particular, he worried that young people would react to the buggy behavior of Windows by becoming sour on the whole edifice of science and technology and would try less hard to learn science. I guess my main objection to "dollar-months per month" and to "kWh per hour" is like that: I worry that it will prevent (via confusion) some fraction of people from learning enough about accounting and the fundamentals of electricity to wield words like "gross revenue", "net revenue", "energy" and "electrical power" effectively. (One of the sources of my worry is my imagining how I personally would've reacted to coming across "kWh per hour" long ago before I had mastered the concepts of watts, energy and power.) To bring this back to where we began, if there are two different quantities of interest, namely, the advertised "capacity" of the panel versus the power a consumer can realistically expect to get out of the panel on a typical day, I would ask that people settle on some short phrases for both -- similar to "gross revenue" and "net revenue" -- and to denominate both quantities in kW (or kWh per month maybe).
quectophoton 2y ago
> because so many people get this wrong. All these terms are just so unintuitive for a mere mortal like me. Energy? Power? The difference between those two words has as much importance to the common person as the difference between "empathy" vs "compassion", or "theory" vs "hypothesis", or "less" vs "fewer". kW being a "stuff over time", but kWh being "amount of stuff"? I don't doubt the math checks out if you expand all units, but I'm as dumb as a wet rock so it took me a while to get this. --- If people wanted me to understand this way sooner, they should have started asking me to think in terms of "kcal" (kilocalories). At least I know that kcal is an "amount of stuff" because it's something you hear if you talk about food. And there's no mention of "hour" anywhere in the name (like with "kWh"), so the name doesn't have anything misleading. Then just tell me that "860.421kcal/h = 1kW" (the numbers don't really matter), and ask me to solve for kcal. When I move the "h" from the left to the right, and the equation becomes "860.421kcal = 1kW * h", everything will click. --- Food has kcal, so kcal is something that can be stored. When the equation has "kcal" on the left, it has "kW * h" on the right, so that means batteries store "kW * h". When I think of "kW" alone, I will remember that the "* h" moved to the left side and became "/h". I might forget stuff, but I know what food is, and I know that there exists an equation, at one side there's "kcal", at the other side there's "kW", and there's an "h" somewhere in there. And "kcal * h" will look wrong af, so I will remember that if the "h" at the left side, it will be "kcal/h". Result: Now I have an intuition for this. (EDIT: Escaping, and add some separators to hopefully make the comment easier to read.)
- IshKebab 2y ago
  > All these terms are just so unintuitive for a mere mortal like me. Energy? Power? Yeah in fairness I think most people never have to deal with these units and they're used interchangeably colloquially. kW = power. This is a rate of work. How quickly work is happening. Intuitively, cycling hard = high power, cycling with low effort = low power. kWh = energy. 1 kWh is literally 1kW for an hour. If you are cycling pretty hard with a power of 0.1 kW for 10 hours, you have generated 1 kWh (0.1 * 10). If you cycle inhumanly hard (0.2 kW) for 3 hours you have generated 0.6 kWh (0.2 * 3). That's it. Now some examples: * Solar panel peak power. This is the maximum power output of the solar panels. For cycling it would be the hardest you can possibly cycle. Apparently the record for cycling is 2.7 kW! (But not for very long; unlike solar panels people get tired.) * Battery capacity. This is in kWh. They store a finite amount of energy. If you have a battery containing 10 kWh you can eek it out slowly - if you only draw 0.1kW from it it will last 100 hours. Or you can dump all the energy in half an hour and it will output 20 kW. The only really complicated one is battery factory output capacity, which approximately 0% of journalists understand. This is measured in Watts... because if you produce 1kWh batteries, and you make one per hour... 1kWh/ 1h is 1 kW! In other words if the batteries from the factory magically came out fully charged and you just used them as a power station without recharging them, then how much power could that power station provide? Yeah that one is a bit confusing.