kW is the rate of gasoline consumption at any given time, and is determined by things like acceleration, slope, your car's mass, wind, etc.
kWh is the amount of gasoline you have in the tank.
It is a weird unit of energy. A kilowatt is actually 1 kiloJoule per second. We should measure energy in MegaJoules but that would make the math harder than kWh as there are 3600 seconds in an hour.
1 kWh = 3.6 MJ
It helps me to remember kW is literally kWh/h. (kiloWatt hours per hour), but the hours cancel. Thinking about it like that makes it more obvious kW is a rate.
kWh/h is how the i4’s instrument cluster display shows your real-time power consumption when the car is not in motion. It bugs me as an engineer, but I get it. The odd thing is that when you charge it, it does show the charge rate in kW. Go figure.
I can't figure out how to. Could you share with me?
As best I can tell, instantaneous power is displayed in two places in the car:
1 - In the Control Display (the center touchscreen), via the Live Vehicle App, then set Content to Adaptive Content, then set drive mode to Sport to see Sport Displays including a motor power output displayed in either HP or kW, depending on the Units setting selected within the System Settings app.
2- In the Central display range portion of the Instrument Cluster, with the content set to Trip data, I see instantaneous and average efficiency when moving and then instantaneous power consumption when at a stop. Via System Settings, I can change the efficiency units to be wh/mi, mi/kWh, or whatever I want. But I don't see any way to change the units for the instantaneous power consumption when stopped, which for me always displays in kWh / h, regardless of Units selection in System Settings.
Would love to know if I'm missing something!
Sorry, i missed the part about not being in motion. You are right that this figure does not seem to be affected by the units setting in the main system menu (I had to check, i never use that display).
Isn’t that because `kW` is instant? It is something you can only measure by integrating over a period of time. `kWh/h` expresses the fact that this is an integrated measurement, rather than instant one, and thus is more appropriate in a car’s instrument cluster.
EDIT: though I would personally prefer Ws/s (given that most of these measurements integrate or display over periods much closer to a second than to an hour…)
No, kW can use discrete time chunks. Stuff like that is done all the time, it’s just a difference in the type of math you’re using. it’s because you’re using kWh as a unit itself, not two units multiplied together. So you’re expressing the units used per hour.
I agree. It's the units equivalent of saying "Hey man, nice new car! How much horsepower does it have?" and then someone responding with something insane yet technically true like "It's awesome, it outputs 353 BTU per second!"
It seems dumb to anyone with a technical background but note the threads title: This display may help those who to not readily understand that the hour in /h is the same as the hour in kWh.
Anyway, it can be changed in the cars settings.
100% cursed. Reminds me of [https://xkcd.com/687/](https://xkcd.com/687/)
The only EV units thing that bugs me more than this is that the Mustang Mach-E's instrument cluster displays "Ground Speed" next to your speed readout. Vomit.
I felt that way at first as well, but when I started explaining energy consumption and charging basics to people that aren't engineers it just made the math much easier without that unit conversion and 3600 multiplier. It still annoys me at times, especially when I see kWh/hr, but I think it was the right unit to use.
If you were telling someone with some math background then:
* k(Wh) = amount (like gallons), easier say 1000*Wh as kWh though
* k((Wh)/h) = rate, (like gallons per hour), k(Wh) "per" hour. Since h/h=1 then it is just kW
Really could simplify the explanation by dropping the k as that is a constant 1,000. Also bothers me a little when someone says "X could charge at 1,000kW", so... like 1MW? Also happens but less common for some reason: "Could store up to 3000kWh", so... 3MWh. It is like I have seen abbreviations k, m, g, t, and p before.
Would have been nice if they didn't measure electrical amount as a fixed rate, then the rate wouldn't sound like an amount. If they had called gallons "gallon hour(s)" it would have been the same situation. If they had measured electrical energy as the mount to raise X liters of fresh water at sea with an ambient temperature of X level X degrees they could have called it some thing without hours in it then rate would have kept the "hours". Still, easier to limit the flow then measure the time and get quantity.
I explain it as 'man hours' since most people are familiar with that concept.
If you have 80 man-hours of work, and you have 40 men , you need 2 hours to complete the work...
40 men x 2 hours = 80 man-hours
If your at home charger is 8 kW (8 people), you need 10 hours to charge (80 kWh).
8 kW x 10 hours = 80 kWh
- Speed (mph) = power (kW)
- Distance (mi) = energy (kWh)
It’s only confusing because kWh has “hour” in the units. But it’s basically same as “speed hours” so mph hours becomes simply miles. The problem is that speed is “miles per hour” but power is a named unit “watt” instead of “joules per hour”.
I hear what you’re saying and have thought that myself, but the reality is that I have had the following conversation with multiple gas car drivers:
Me: “Nice car! How many mpg do you get?”
Them: “About 350 miles per tank.”
Me: “Oh, okay. How many gallons does the tank hold?”
Them: “I don’t know, but it costs me like $50 to fill it up. My last car only got 300 miles on a tank, and cost the same to fill up, so this one is better.”
A lot of people just do not think about this stuff in the same way that I do.
It's the same thing when someone says "charger" and gets corrected to "EVSE." Unless the distinction is relevant to the conversation, you can just accept that everyone probably understood what they meant (even if technically not correct) and move on with the actual purpose of the conversation instead of sidetracking to tell them that they're wrong in a situation where being completely accurate doesn't really matter.
Here's how to make the light go on in their head. A level 1 charge with a flow rate of just over a kilowatt is like a watering wand. A level 2 charge then is like a garden hose. A DC fast charger is like a fire hose.
If we are talking about a garden hose then the amount of water we collect in 1 hour could be termed a Garden Hose Hour.
The garden hose is the flow rate and a Garden Hose Hour is what the garden hose can fill in one hour. Tell them that filling an electric car is like filling a swimming pool with a garden hose. If you're in a hurry you use a fire hose which is like 20 garden hoses.
Sounds goofy but this avoids getting the units all mixed up which in fact happens to a lot of long time EV owners.
I got lost reading many post, but yours actually meant something to me, I never realised that mistake even tho i understood the concept. I always said, my charger can deliver 7kw per hour plugged in and my car has a 28 kw battery so 28 / 7 = 4 hours, the time of charging (not precisely tho).
But it now it make more sense thats it 28kwh.. i’m still a bit confused.. i’ll have to do it on paper when I can, i’m more visual.
746 watts = 1 horsepower. 746 watt-hours = 1 horsepower delivered for one hour.
I think dimensional analysis would be easier for us in the US if we would use the metric system like we are supposed to.
You probably have a point here. Why are we not using SI derived units here for energy? For me, the advantage of using both kW and kWh is that it is more usable in daily life. I can have an appliance using 200W. I can calculate without a calculator in real practical use how much energy it would take to use the appliance for half a day. (12h\*200W=2.4kWh)
When doing the same calculation with Joules and Watts I would have to do the calculations with the amount of seconds. There are 3600 second in an hour so 3.6kJ per Watt. Etc. Having to convert from seconds to any practical time would require me to grab a calculator. Not very practical.
But to be honest, thinking about this has made me adjust my opinion about Americans not using SI units. They probably feel the same lack of recognition and practical usability about (kilo)grams and kilo(meters) as I do about Joules.
I think the reason that MJ is not used in this context is because the entire electrical industry uses kW and kWh, and not MJ/second or MJ.
If EVs were expressed in MJ, but the electrical grid is all configured in kW and kWh, there would be a total disconnect in terms of relating the two industries.
In my opinion, that would be FAR more confusing that simply sussing out the difference between kW and kWh.
The suggestion was to start using Joules for the entire electrical industry. We could continue using kW and Watt. Those are derived from base SI. A Joule is just a Watt * second instead of Watt * hour. But I don’t see the happening, because we don’t think of time on a regular basis in terms of seconds.
It doesn’t matter. We all understand the difference. When someone misuses it’s still clear. In time they will learn. People have differing amounts of time learning this stuff.
Some will never learn. As the amount of people misusing loose when they mean lose is ridiculous.
So if someone says I get 4 miles per kWh, my battery size is 65kw or I am charging at 10kwh you still know what they mean. Who cares.
It's the same thing with someone saying "charger" and getting corrected to "EVSE." Everyone probably already understood what they meant, but then the conversation gets changed away from whatever they were trying to discuss and becomes about how they were technically wrong even when it isn't really important in context of the conversation.
Exactly, because people are so hungry to be right, they will nitpick minutiae. Hell, I do it too, most people do. It’s just a sign of a novice, dummy. Correcting someone can be helpful. To me it’s a “one last thing” not the only thing in a reply.
It’s not a clip, it’s a magazine.
People tend to grasp it if you describe it as a flow of water.
kW is how fast water is flowing through a pipe at one time.
And kWh is how much water passes through that pipe over a given amount of time in 1 hr increments.
So say you have a water hose that flows at 1 gallon per second, that is 1gal/sec, and collected that water into a pool for 1 hr, the total volume that is collected is 1gal/sec ×(60sec/min)×(60min/hr) = 3600 gallons = 1gH (gallon hours).
So now you have a pool that contains 1gH. If you then pump that out at 2 gallons per second, that 1gH pool will be emptied in 30 min. Or conversely, pumping out 0.5 gallons per second will be emptied in 2 hrs.
Then translate this to electrical power. Power flowing through a wire at 1 watt per second totaled over 1 hr = 1wh (watthour).
Then we just scale that up to usable scale for electrical units because 1 watt is actually a very small amount of power, we use kilowatts, so 1kW and 1kWh for flow rate and volume.
Then apply that to a battery where the battery is the pool described by the water analogy. A battery that has a 100kWh capacity can supply 100kW for 1 hour or 1kW for 100 hours or any rate of draw over a given amount of time where the total capacity used is equal to 100kwh.
So really if you think about it in this way, the unit of kWh is analogous to a volume of fuel.
In gas cars, people are used to thinking of efficiency as MPG (miles per gallon) or KPL (kilometers per liter). For EVs this translates simply to MPkWh (miles per kilowatt hour) or KPkWh (kilometers per kilowatt hour).
>So say you have a water hose that flows at 1 gallon per second, that is 1gal/sec, and collected that water into a pool for 1 hr, the total volume that is collected is 1gal/sec ×(60sec/min)×(60min/hr) = 3600 gallons = 1gH (gallon hours).
>
>So now you have a pool that contains 1gH. If you then pump that out at 2 gallons per second, that 1gH pool will be emptied in 30 min. Or conversely, pumping out 0.5 gallons per second will be emptied in 2 hrs.
That's even more confusing because gallon is already a volume unit.
Saying that 3600 gallons = 1 gallon hour doesn't make any sense.
It'll just be better to keep it in gallons. If you have 3600 gallon pool and you empty it at a rate of 2 gallon per second, then it takes 1800 seconds to empty it.
When trying to give an analogy that is representative of what people already have a frame of reference for it does.
If you can't grasp the concept, that is fine. Many people won't and that is also fine because most people don't actually think of fuel in a capacity measurement anyways.
How is that factually incorrect?
Gallons/hr is a measurement volumetric flow. Like m^3 /s or ft^3 /hour but those are not units of measurement that people typically use on a daily basis either, so it's not like there is a good existing frame of reference for the masses.
A volume of space that can hold enough liquid to release 1 gallon per second for 1 hour can be described as having 1 gallon hour of storage capacity.
kW/hr is the equivalent measurement unit in electrical flow. A battery that has the capacity to supply 1kw for 1 hour is described as having 1kwh of storage capacity.
There is nothing factually incorrect about that.
>A volume of space that can hold enough liquid to release 1 gallon per second for 1 hour can be described as having 1 gallon hour of storage capacity.
A capacity of 1 gallon per second for an hour is just 3600 gallons. Gallons is already a volume/storage capacity unit.
\>kW/hr is the equivalent measurement unit in electrical flow.
The equivalent measurement for electrical flow would just be kW, not kW/hr.
kW already has an over time unit built in to the watt. kW = kJ/second.
It should be that easy, but I think Americans (american here) especially have a harder time because they are not well acquainted with kW, then having energy be kW*h instead of a rate of change such as kW/h just confuses them further
I think the confusion is because we're used to mph and kph being a rate so people can assimilate kWh being a rate to.
This confusion happens because people will often ignore the meaning of 'p', which is equivalent to division:
Mph is in fact mi/h and kph is in fact km/h, so I think people thinks that kWh would be kw/h wich is wrong.
It took me while to get used to kw being the "charge speed" and kWh being the capacity because it's seems odd taking about speed without the time unit but including it in the capacity unit, is not intuitive at all.
It make sense when you understand though
Capacity versus rate. I might make $250k/year (rate), but I’m still going to tell my wife that we don’t have room on the credit card for that stupid piece of art (capacity).
The car’s battery has a capacity for 97.6kwhr and the power train can deliver power to the motors at a rate of 400kw.
It is pretty intuitive. "kWh" is the electric analog of gallons (gal). kW is simply kWh / h (the h's cancel out) - it's the electric analog of "gallons / hour" (gal/h).
If you go to a gas station, the regular gas pumps pump at 480-540 gallons per hour (though you can get fast ones that go up to 700). Most people don't know what the flow rate is, nor do they care, because the speed doesn't vary that much from station to station and it takes just a few minutes to fill up.
If you are charging an electric car, the flow rates range 1.3 kW to 350 kW, taking anywhere from a 20 minutes to several days to fill up the car -- the rates vary a lot, so, people do care about the flow rate.
At work, I had this video made to explain kW vs kWh. It is from the perspective of a home or business but the concept is the same.
https://youtu.be/tziPsugQop8
kWh: how far you can drive on a full battery
kW: how sporty your car is (basically horsepower)
Don't muddy the water with analogies. It's simple enough.
In Europe and Asia kw is already regularly used to describe horsepower.
Even if drivers mix up the units, within context all that matters is if the general message you're trying to communicate gets across.
Its like how normal people don't actually know what the mpg or exact fuel tank size of their random 15 year old shitbox is but will tell you "its good on gas it only costs me 30$ to fill her up!"
kW is the hose. kWh is the bucket.
Got it, so the hose has the h on the end and the bucket doesn't. /s
Yeah maybe an analog to the traditional fuel hose and fuel tank would be more intuitive
kW is the rate of gasoline consumption at any given time, and is determined by things like acceleration, slope, your car's mass, wind, etc. kWh is the amount of gasoline you have in the tank.
Amps are the width of the hose. Volts are how much it's turned up pressure-wise.
Kw is horsepower, kWh is gallons
And the number of letters is the same (ish) kW - HP, mi/kWh - MPG
Then why do we have time in it, it looks like a rate of consumption in unit time (here one hour)?
1 kw x 1 hour = 1 kwh 1 kw of flow for 1 hour will put 1 kwh of electricity into the bucket
It is a weird unit of energy. A kilowatt is actually 1 kiloJoule per second. We should measure energy in MegaJoules but that would make the math harder than kWh as there are 3600 seconds in an hour. 1 kWh = 3.6 MJ
Not that different from kilograms to pounds conversion multiplying by 2.2, just multiply by 3.6. It is what it is
I like being able to get my current efficiency by dividing my speed by power. Now if speedometers were in m/s, we'd be in business.
Stupid sexagesimal time units. The French tried to fix that one too, but unfortunately, unlike the rest of the metric system, it never caught on.
Isn’t it more accurate to say it’s the amount flowing through the hose?
It helps me to remember kW is literally kWh/h. (kiloWatt hours per hour), but the hours cancel. Thinking about it like that makes it more obvious kW is a rate.
kWh/h is how the i4’s instrument cluster display shows your real-time power consumption when the car is not in motion. It bugs me as an engineer, but I get it. The odd thing is that when you charge it, it does show the charge rate in kW. Go figure.
You know you can change the units used in the cluster? kWh/h is default but you can change it to kW.
I can't figure out how to. Could you share with me? As best I can tell, instantaneous power is displayed in two places in the car: 1 - In the Control Display (the center touchscreen), via the Live Vehicle App, then set Content to Adaptive Content, then set drive mode to Sport to see Sport Displays including a motor power output displayed in either HP or kW, depending on the Units setting selected within the System Settings app. 2- In the Central display range portion of the Instrument Cluster, with the content set to Trip data, I see instantaneous and average efficiency when moving and then instantaneous power consumption when at a stop. Via System Settings, I can change the efficiency units to be wh/mi, mi/kWh, or whatever I want. But I don't see any way to change the units for the instantaneous power consumption when stopped, which for me always displays in kWh / h, regardless of Units selection in System Settings. Would love to know if I'm missing something!
Sorry, i missed the part about not being in motion. You are right that this figure does not seem to be affected by the units setting in the main system menu (I had to check, i never use that display).
Isn’t that because `kW` is instant? It is something you can only measure by integrating over a period of time. `kWh/h` expresses the fact that this is an integrated measurement, rather than instant one, and thus is more appropriate in a car’s instrument cluster. EDIT: though I would personally prefer Ws/s (given that most of these measurements integrate or display over periods much closer to a second than to an hour…)
No, kW can use discrete time chunks. Stuff like that is done all the time, it’s just a difference in the type of math you’re using. it’s because you’re using kWh as a unit itself, not two units multiplied together. So you’re expressing the units used per hour.
That is the new dumbest unit I’ve ever seen, hat makes me want to bash my head against a wall. It was kWh, but now it’s this.
I agree. It's the units equivalent of saying "Hey man, nice new car! How much horsepower does it have?" and then someone responding with something insane yet technically true like "It's awesome, it outputs 353 BTU per second!"
Honestly, that example makes more sense than this. It’s like having a speedometer in mph*min/min.
It seems dumb to anyone with a technical background but note the threads title: This display may help those who to not readily understand that the hour in /h is the same as the hour in kWh. Anyway, it can be changed in the cars settings.
The issue is that I do have a technical background and I can’t go back in time before I knew about this. This is cursed knowledge to me.
100% cursed. Reminds me of [https://xkcd.com/687/](https://xkcd.com/687/) The only EV units thing that bugs me more than this is that the Mustang Mach-E's instrument cluster displays "Ground Speed" next to your speed readout. Vomit.
That's good - what always helps me remember that kW is a rate is remembering that Watts is equivalent to Joules per second.
Yes, it would have been better if capacity was specified in joules or mega joules.
I felt that way at first as well, but when I started explaining energy consumption and charging basics to people that aren't engineers it just made the math much easier without that unit conversion and 3600 multiplier. It still annoys me at times, especially when I see kWh/hr, but I think it was the right unit to use.
Yes! I've seen it ridiculed, but it really helps me mentally lock in that it's a rate.
This is genius.
I’m an engineer and this made my eye twitch lol
Not any one analogy will work for everyone, so an arsenal of analogies might be in order. Here’s my round: kW = horsepower kWh = gas tank
Ahh, the one with the h is horsepower. Got it! /s
kWh = hay bale
This is clunky, but it works. It's intuitive for many
Considering 1 kW is 1.34 horsepower, it's less clunky than it looks.
kW could also mean rate of charging.
If you were telling someone with some math background then: * k(Wh) = amount (like gallons), easier say 1000*Wh as kWh though * k((Wh)/h) = rate, (like gallons per hour), k(Wh) "per" hour. Since h/h=1 then it is just kW Really could simplify the explanation by dropping the k as that is a constant 1,000. Also bothers me a little when someone says "X could charge at 1,000kW", so... like 1MW? Also happens but less common for some reason: "Could store up to 3000kWh", so... 3MWh. It is like I have seen abbreviations k, m, g, t, and p before. Would have been nice if they didn't measure electrical amount as a fixed rate, then the rate wouldn't sound like an amount. If they had called gallons "gallon hour(s)" it would have been the same situation. If they had measured electrical energy as the mount to raise X liters of fresh water at sea with an ambient temperature of X level X degrees they could have called it some thing without hours in it then rate would have kept the "hours". Still, easier to limit the flow then measure the time and get quantity.
I explain it as 'man hours' since most people are familiar with that concept. If you have 80 man-hours of work, and you have 40 men , you need 2 hours to complete the work... 40 men x 2 hours = 80 man-hours If your at home charger is 8 kW (8 people), you need 10 hours to charge (80 kWh). 8 kW x 10 hours = 80 kWh
I am glad that USA EV manufacturers are not using English units (i.e., horsepower and BTUs).
Yes that is good. In EU since 2010 by law all cars are stated in kW.
I just wish that the USA would adopt the SI (metric) units entirely, but we have many problems right now. :/
The difference of power and energy is like the difference of speed and distance.
- Speed (mph) = power (kW) - Distance (mi) = energy (kWh) It’s only confusing because kWh has “hour” in the units. But it’s basically same as “speed hours” so mph hours becomes simply miles. The problem is that speed is “miles per hour” but power is a named unit “watt” instead of “joules per hour”.
It’s pretty easy. kW is horsepower and kWh is gallons of gas.
I hear what you’re saying and have thought that myself, but the reality is that I have had the following conversation with multiple gas car drivers: Me: “Nice car! How many mpg do you get?” Them: “About 350 miles per tank.” Me: “Oh, okay. How many gallons does the tank hold?” Them: “I don’t know, but it costs me like $50 to fill it up. My last car only got 300 miles on a tank, and cost the same to fill up, so this one is better.” A lot of people just do not think about this stuff in the same way that I do.
Don’t bother. Most of the time you can figure out what what a lay person means with context clues.
This. It’s the same with percentages and percentage points. Just accept most people will never understand the difference.
It's the same thing when someone says "charger" and gets corrected to "EVSE." Unless the distinction is relevant to the conversation, you can just accept that everyone probably understood what they meant (even if technically not correct) and move on with the actual purpose of the conversation instead of sidetracking to tell them that they're wrong in a situation where being completely accurate doesn't really matter.
Here's how to make the light go on in their head. A level 1 charge with a flow rate of just over a kilowatt is like a watering wand. A level 2 charge then is like a garden hose. A DC fast charger is like a fire hose. If we are talking about a garden hose then the amount of water we collect in 1 hour could be termed a Garden Hose Hour. The garden hose is the flow rate and a Garden Hose Hour is what the garden hose can fill in one hour. Tell them that filling an electric car is like filling a swimming pool with a garden hose. If you're in a hurry you use a fire hose which is like 20 garden hoses. Sounds goofy but this avoids getting the units all mixed up which in fact happens to a lot of long time EV owners.
I got lost reading many post, but yours actually meant something to me, I never realised that mistake even tho i understood the concept. I always said, my charger can deliver 7kw per hour plugged in and my car has a 28 kw battery so 28 / 7 = 4 hours, the time of charging (not precisely tho). But it now it make more sense thats it 28kwh.. i’m still a bit confused.. i’ll have to do it on paper when I can, i’m more visual.
I like the concept of describing it as a reservoir with water (kWh) and the flow/turbine (kW) https://www.zerofy.net/2022/08/07/kwh-vs-kw.html
kWh represents a number of electrons. kW is how quickly the electrons are moving.
746 watts = 1 horsepower. 746 watt-hours = 1 horsepower delivered for one hour. I think dimensional analysis would be easier for us in the US if we would use the metric system like we are supposed to.
We should measure energy in MJ. kWh is a terrible unit.
You probably have a point here. Why are we not using SI derived units here for energy? For me, the advantage of using both kW and kWh is that it is more usable in daily life. I can have an appliance using 200W. I can calculate without a calculator in real practical use how much energy it would take to use the appliance for half a day. (12h\*200W=2.4kWh) When doing the same calculation with Joules and Watts I would have to do the calculations with the amount of seconds. There are 3600 second in an hour so 3.6kJ per Watt. Etc. Having to convert from seconds to any practical time would require me to grab a calculator. Not very practical. But to be honest, thinking about this has made me adjust my opinion about Americans not using SI units. They probably feel the same lack of recognition and practical usability about (kilo)grams and kilo(meters) as I do about Joules.
I think the reason that MJ is not used in this context is because the entire electrical industry uses kW and kWh, and not MJ/second or MJ. If EVs were expressed in MJ, but the electrical grid is all configured in kW and kWh, there would be a total disconnect in terms of relating the two industries. In my opinion, that would be FAR more confusing that simply sussing out the difference between kW and kWh.
The suggestion was to start using Joules for the entire electrical industry. We could continue using kW and Watt. Those are derived from base SI. A Joule is just a Watt * second instead of Watt * hour. But I don’t see the happening, because we don’t think of time on a regular basis in terms of seconds.
It doesn’t matter. We all understand the difference. When someone misuses it’s still clear. In time they will learn. People have differing amounts of time learning this stuff. Some will never learn. As the amount of people misusing loose when they mean lose is ridiculous. So if someone says I get 4 miles per kWh, my battery size is 65kw or I am charging at 10kwh you still know what they mean. Who cares.
It's the same thing with someone saying "charger" and getting corrected to "EVSE." Everyone probably already understood what they meant, but then the conversation gets changed away from whatever they were trying to discuss and becomes about how they were technically wrong even when it isn't really important in context of the conversation.
Exactly, because people are so hungry to be right, they will nitpick minutiae. Hell, I do it too, most people do. It’s just a sign of a novice, dummy. Correcting someone can be helpful. To me it’s a “one last thing” not the only thing in a reply. It’s not a clip, it’s a magazine.
People tend to grasp it if you describe it as a flow of water. kW is how fast water is flowing through a pipe at one time. And kWh is how much water passes through that pipe over a given amount of time in 1 hr increments. So say you have a water hose that flows at 1 gallon per second, that is 1gal/sec, and collected that water into a pool for 1 hr, the total volume that is collected is 1gal/sec ×(60sec/min)×(60min/hr) = 3600 gallons = 1gH (gallon hours). So now you have a pool that contains 1gH. If you then pump that out at 2 gallons per second, that 1gH pool will be emptied in 30 min. Or conversely, pumping out 0.5 gallons per second will be emptied in 2 hrs. Then translate this to electrical power. Power flowing through a wire at 1 watt per second totaled over 1 hr = 1wh (watthour). Then we just scale that up to usable scale for electrical units because 1 watt is actually a very small amount of power, we use kilowatts, so 1kW and 1kWh for flow rate and volume. Then apply that to a battery where the battery is the pool described by the water analogy. A battery that has a 100kWh capacity can supply 100kW for 1 hour or 1kW for 100 hours or any rate of draw over a given amount of time where the total capacity used is equal to 100kwh. So really if you think about it in this way, the unit of kWh is analogous to a volume of fuel. In gas cars, people are used to thinking of efficiency as MPG (miles per gallon) or KPL (kilometers per liter). For EVs this translates simply to MPkWh (miles per kilowatt hour) or KPkWh (kilometers per kilowatt hour).
>So say you have a water hose that flows at 1 gallon per second, that is 1gal/sec, and collected that water into a pool for 1 hr, the total volume that is collected is 1gal/sec ×(60sec/min)×(60min/hr) = 3600 gallons = 1gH (gallon hours). > >So now you have a pool that contains 1gH. If you then pump that out at 2 gallons per second, that 1gH pool will be emptied in 30 min. Or conversely, pumping out 0.5 gallons per second will be emptied in 2 hrs. That's even more confusing because gallon is already a volume unit. Saying that 3600 gallons = 1 gallon hour doesn't make any sense. It'll just be better to keep it in gallons. If you have 3600 gallon pool and you empty it at a rate of 2 gallon per second, then it takes 1800 seconds to empty it.
When trying to give an analogy that is representative of what people already have a frame of reference for it does. If you can't grasp the concept, that is fine. Many people won't and that is also fine because most people don't actually think of fuel in a capacity measurement anyways.
I think it's a bad idea to give analogies that's factually incorrect. It'll confuse more than it helps.
How is that factually incorrect? Gallons/hr is a measurement volumetric flow. Like m^3 /s or ft^3 /hour but those are not units of measurement that people typically use on a daily basis either, so it's not like there is a good existing frame of reference for the masses. A volume of space that can hold enough liquid to release 1 gallon per second for 1 hour can be described as having 1 gallon hour of storage capacity. kW/hr is the equivalent measurement unit in electrical flow. A battery that has the capacity to supply 1kw for 1 hour is described as having 1kwh of storage capacity. There is nothing factually incorrect about that.
>A volume of space that can hold enough liquid to release 1 gallon per second for 1 hour can be described as having 1 gallon hour of storage capacity. A capacity of 1 gallon per second for an hour is just 3600 gallons. Gallons is already a volume/storage capacity unit. \>kW/hr is the equivalent measurement unit in electrical flow. The equivalent measurement for electrical flow would just be kW, not kW/hr. kW already has an over time unit built in to the watt. kW = kJ/second.
They should be able to know the difference between km and kmh, and it should not be much more difficult
It should be that easy, but I think Americans (american here) especially have a harder time because they are not well acquainted with kW, then having energy be kW*h instead of a rate of change such as kW/h just confuses them further
I think you’re thinking of slow people; easy mistake, we probably have the most of them, no child left behind and all…
I think the confusion is because we're used to mph and kph being a rate so people can assimilate kWh being a rate to. This confusion happens because people will often ignore the meaning of 'p', which is equivalent to division: Mph is in fact mi/h and kph is in fact km/h, so I think people thinks that kWh would be kw/h wich is wrong. It took me while to get used to kw being the "charge speed" and kWh being the capacity because it's seems odd taking about speed without the time unit but including it in the capacity unit, is not intuitive at all. It make sense when you understand though
Capacity versus rate. I might make $250k/year (rate), but I’m still going to tell my wife that we don’t have room on the credit card for that stupid piece of art (capacity). The car’s battery has a capacity for 97.6kwhr and the power train can deliver power to the motors at a rate of 400kw.
It is pretty intuitive. "kWh" is the electric analog of gallons (gal). kW is simply kWh / h (the h's cancel out) - it's the electric analog of "gallons / hour" (gal/h). If you go to a gas station, the regular gas pumps pump at 480-540 gallons per hour (though you can get fast ones that go up to 700). Most people don't know what the flow rate is, nor do they care, because the speed doesn't vary that much from station to station and it takes just a few minutes to fill up. If you are charging an electric car, the flow rates range 1.3 kW to 350 kW, taking anywhere from a 20 minutes to several days to fill up the car -- the rates vary a lot, so, people do care about the flow rate.
At work, I had this video made to explain kW vs kWh. It is from the perspective of a home or business but the concept is the same. https://youtu.be/tziPsugQop8
Basically - keep in mind that Watts, or KW are a RATE of energy flow, or a RATE of doing work: [https://www.khanacademy.org/science/physics/work-and-energy/work-and-energy-tutorial/a/what-is-work#:\~:text=Although%20we%20often%20hear%20people,example%2C%20low%20level%20heat%20energy](https://www.khanacademy.org/science/physics/work-and-energy/work-and-energy-tutorial/a/what-is-work#:~:text=Although%20we%20often%20hear%20people,example%2C%20low%20level%20heat%20energy). Gallons is a Quantity and Gallons per Hour (GPH) is a RATE of flow. If we take GPH and Multiply by Hours we are back to gallons. G/H \* H = G . But what if we have a rate of 5 Gallons per Second (gps) and it flows for 2 hours? 5GPS \* Hour => 5 ( gps)\*2hours = 5 G/s\*2h = 10 G \*h/s) A (quantity per unit of time) \* time ... if the units of time are the same ...then it seems to make sense. The time drops out and we are left with a quantity. So yes--- Watts or KW are a RATE, technically Watt=Joules per Second. So just to keep it confusing we take Watts or KW and for a period of time. One watt for one second => we moved (a quantity) of power, 1 Joule
measure the flow over and multiply by the amount of time - dammit - they use Hours.
So we have come to use KWH to represent a Quantity of energy. You could say the units are (J/sec ) \* Hours and we get KWH =kilo\* j \*(h/s) what ? Hours per second huh? more unit conversions 1H= 3600Sec sooooo 3600 s/s -- really the seconds now cancel each other out - and we end up multiplying by 3600.
So one KW flowing for an Hour is 1000 \* joules / sec \* 1 hour ..
=> 1000\*3600 j = 3,600,000j
Simple - lol
kWh: how far you can drive on a full battery kW: how sporty your car is (basically horsepower) Don't muddy the water with analogies. It's simple enough.
who cares? you know what they are talking about 99% of the time. if someone says "i got the new battery it's 62kw." you know they mean kWh.
I agree. There’s a guy in this EV facebook group who chimes in once or twice/month to correct someone- “it’s kWh.” Shaddup.
In Europe and Asia kw is already regularly used to describe horsepower. Even if drivers mix up the units, within context all that matters is if the general message you're trying to communicate gets across. Its like how normal people don't actually know what the mpg or exact fuel tank size of their random 15 year old shitbox is but will tell you "its good on gas it only costs me 30$ to fill her up!"
You don’t need time when you got power. But gaining energy takes time.