Update: I am actually searching for really simple, intuitive ways to explain it. I have a background in engineering, but am struggling to explain why we “pay for kwh”, and not kw (on our electricity bill) to someone who doesn’t. I have tried in many ways but maybe I’m not giving the right examples or making the right comparisons. I am really searchig for a way to ELI5.
In: 24
Think of KW as the capacity of a pipe and KWH as the amount you consumed. That’s why you pay by KWH while KW defines the peak max rate at which you can consume.
KW says how much power is used each second. If a device uses 1kw and is turned on for 1 hour, it has used 1kwh. When you turn on the same device for a half hour it has used 0,5kwh.
Kw can be compared to the amount of water flowing out of the crane each second. But you are charged per the netto amount of water used, kWh can be compared to liters in this example.
I’d compare it to water usage.
You pay for water by the amount you’ve used, not the flow rate. And that in essence is the kWh vs the kW.
edit: I’ll expand this answer out…
If I want to fill a (small) swimming pool with a hose pipe, I can turn on the tap by any amount I want to up to the max. I could drip water in, or I could just fully open the tap. The end result will be the same though – I end up with a full swimming pool. It’s just if I drip water in it will take much, much longer. BUT if I know the amount of time it’s taken to fill the swimming pool and the flow rate of water, I can work out the total water usage.
So, in this case, I have the water flow rate (cubic meters per second) multiplied by time (hours). There is a mix of time units (seconds and hours) which don’t easily cancel out.
Electricity is the same. Note first that a Watt is defined as **Joules per second**. So I have a flow rate (kW). I also have the amount of time I’m using that flow rate for (hours). So if I want to know the total usage I multiply the two together: kWh.
How quickly I fill a jug is the measure of KW (kilowatts).
How much the jug can hold is the KWh (kilowatthour)
I often use the analogy with a water tap and a bucket. Power is best associated with how much you open the tap, while energy is how much the bucket is filled with water.
This way it’s easy to figure out how you can have accumulated (or spent) a lot of energy even with very little power, because it also depends on time.
May not be 100% accurate but you get the idea. HTH.
KW is power and kWh is energy. Power is the rate that energy is being provided at.
You pay for how much energy you consume. The rate it is supplied at doesn’t matter.
It’s like pay is 15 dollars an hour, but you get a paycheck depending on how many hours you work.
Would it be fair to charge the same to 2 people?
One has their 1KW electric fire on for an hour.
The other has their 1KW electric fire on for 2 hours. They used twice as much electricity so they pay twice as much.
kW is instantaneous power. How much work you are doing right now.
kWh is energy, how much energy you burned over a time period. Could kind of be considered the average power over an hour. Using 1kW for an hour constantly uses the same energy as using 2kW for only 30 mins.
You can think of riding a bike. How hard you pedal is the power, it’s kW (though in reality good luck pedalling at 1kW for any extended period!). By the end of the cycle the energy you burned can be measured in kWh. Pedalling at 1kW for an hour burns more energy than pedalling at 0.5kW for an hour.
Also worth mentioning that energy is power X time. You literally multiply the kW by how many hours to get the energy (though usually you’d measure in Joules, which uses seconds not hours).
One is a unit of energy and the other is a unit of power.
Energy is, I believe, a pretty intuitive concept. You spend energy to make things happen. It’s what battery capacity is measured in.
Power is just a measure of how fast energy is being used by something. In other words, energy per unit time. Kind of like how speed is how much distance you cover per unit time.
The SI system unit for power is the watt (W). One watt of energy isn’t actually all that much; in home electrical systems, it’s much more common to refer to watts in the thousands, also known as kilowatts (kW). In an electrical context, a measurement in kilowatts will tell you how power-hungry an appliance is. How much energy it must consume per second to do its work.
The SI unit for energy is the joule (J). One watt is one joule used up per second. As we said before, one watt isn’t actually a lot. Most electrical appliances measure their power draw in kilowatts. One kilowatt consumed over the course of one second would be one kilojoule (kJ). But that’s still a little… unhelpful. One second isn’t a very long time to measure power consumption over. People interested in knowing how much power something has consumed (like, say, your electric company) want to work in bigger units, like… whole hours. An hour has 3,600 seconds in it. So a thousand watts consumed continuously over 3,600 seconds makes 3,600,000 joules, or 3.6 megajoules (MJ). That’s still a somewhat clumsy unit, since now it’s really big and has that awkward factor of 3.6 in it. So what they instead do is say “you’ve used one kilowatt over the course of an hour”, which they will measure as one “kilowatt-hour” (kWh). It’s measuring the same thing as joules, just in a unit that’s more convenient for the electric company to measure and bill you for.
The standard unit of energy is the Joule. Joules could be used to describe the energy stored in a battery, in a gallon of gasoline, in food (Calories are also a unit of energy), and so on. Energy being transferred over time is such a commonly used concept, that we gave the unit its own name: the Watt. 1 Watt = 1 Joule per second.
1 Watt is actually a small amount, so often we use kilowatts (kW) instead. 1 kW = 1000 W = 1000 J/s.
A kilowatt-hour is the amount of energy needed to transfer energy at 1000 Watts for an hour. There are 3600 seconds/hour, so 1 kWh =1 kJ/s * 1 hour = 1 kJ/s * 3600 seconds = 3600 kJ = 3.6 MJ.
We often use kWh instead of megajoules because we want to answer questions like “how many hours will my battery last?” and not “how many seconds will my battery last?”. They’re technically equivalent, but kWh is more convenient.
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