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
If you bike super hard, you might get 400w of output. This is the energy you are able to dump into biking every instant. It’s an instantaneous measure of how hard you are working. The very next second you might cool it a bit and drop to 300w.
If you bike really hard at 400w for an hour, then the cumulative energy you’ve output is 400Wh
Kw is how far you open the tap.
KwH is how long the tap is open.
0.5Kw for 1 hour is 0.5KwH 0.5Kw for half an hour is 0.25KwH
My take on breaking this down, as an analogy. Lets think of it as water.
KW is the power. It’s how fast the energy (water) is delivered.
– Is it a steady dribble from a faucet or a blast from a fire hose?
The provider doesn’t really care how fast you consume the water. That’s your business. What they care about is how *much* water they supplied.
KWh is the actual energy provided. Here “liters” is the same as “joules of energy”
– A dribble for an entire day is 10 L.
– A short blast from a fire hose is 10 L
The company again, doesn’t care how fast you obtained the product (water/energy) just specifically how much they had to give you.
Another version of this problem:
Power (KW) is a Rate, like speed. KWH is energy, a quantity. It’s Joules, just expressed oddly. This would be like distance.
So a transportation company charges you based on how far you want to go (KWH) and is far less interested in how fast you get there. usually.
Now if you want to get there very, very fast, you pay a premium, but even then the exact speed isn’t a concern. But special measures need to be taken for very high speeds/rates, so you pay for those special measures.
A watt is a unit of power; something using 1W uses 1 joule of energy every second. 1 kW is then 1,000 watts or 1,000 J (1kJ) being consumed every second.
A kilowatt-hour is a unit of energy; it’s the energy consumed by using 1,000 watts for a period of 1 hour. Thus 1 kWh is the equivalent of 1000*60*60 = 3.6 megajoules of energy.
I always think of an electric kettle. It consumes 3 kW when on but it only runs for like 2 minutes. So boiling water costs 3 kWh * 2 mins = 0.1 kWh or about 1 cent. Compare this to a modern light bulb: it consumes just 0.01 kW but is on for 10 hours a day, so we get the same 0.1 kWh.
This example shows that two things matter for overall energy consumption (kWhs): power (watts) and time the appliance is on.
KW is ambiguous from financial perspective. For example, if I tell X uses 1kw, you don’t really know how much you have to pay for it at the end of the day. kWh include this information. If I tell you X uses 1kwh you can easily calculate your cost.
It’s like the difference between speed and distance travelled, where speed would be the kw and distance would be the kwh. When you pay for travel you generally pay for how far you go rather than the speed of the journey.
When you fill your car up with fuel, they don’t charge by how fast the fuel goes into the car (kw) but rather by the speed it goes into your car multiplied by the time you spend doing that, which is the amount (kwh).
It’s rate vs. amount. You have to maintain a rate over a period of time to achieve something.
As an example use traveling in a car. Rate would be equivalent to speed say 60 mph. But it’s only by going 60mph for a while that you get somewhere. Say you’ve travelled 60 miles, you have to maintain 60mph for an hour to get there (amount). Let’s say I hop in a cab and want to go somewhere. If I paid by rate he/she could simply accelerate to 60mph and then stop and ask for money. When I get in a cab I want to go somewhere so I am paying for he/she to maintain a rate over a period of time to actually cover the distance desired.
Joules (J) is the unit of for energy.
A watt (W) is energy consumption per second, J/s.
kW is just 1000 watt.
Wh is again just energy, (J/s)*h = (J/s)*s*36000 = 3600 J
So kWh is 3600 kW which is 3.6 MW
Something that uses a watt to run will consume 1 watt hour in 1 hour, and 24 watt hours a day.
I can see why it’s a bit confusing because we rate something’s power in how much power it uses in an hour.
If you had a 10 kWh battery, you could power a 1kw load for 10 hours
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