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.
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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.
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.
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
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
Turn your heater on? It’s drawing 1kW = 1000 watts.
Turn it off after a second? Zero watts now in use.
Turn it on for an hour? You’ve used 1kWh of power.
Another analogy is horsepower in cars. Horsepower is like kW, the actual strength. The work the car did, like pulling its weight over some distance, is like kWh.
W is watt its a measure of power E/t energy per time often expressed is J/s.
KW is a kilowatt its a 1000 watts.
KWh is a measure of energy, if power is P = E/t then P×t = E×t / t = E. So J/s × s = J. 1 KW is 1000 J/s and 1000 J/s × 3600s (1h) = 3 600 000 J of energy. If your electric device consumes 500 W of power in 2 hours it would have consumed 1 KWh of energy.
A kilowatt is 1,000 joules per second. A joule is just a standard unit of energy. If you express kilowatt as the fraction 1,000 joules / 1 second, then multiply that by 1 hour (3,600 seconds), you find that the seconds unit cancels out. One kWh is the same thing as saying 3,600,000 joules of energy.
Electricity is measured in watts, because it is really easy to use when working with electricity. Watts = volts * amps. If you know your voltage and amperage, you know the watts. If you know the watts and how long you pulled those watts, you know how much energy you used.
For instance (making all of these numbers up). If you have an electric motor that operates at 9 volts and draws 2 amps, you know you need 9 volts * 2 amps = 18 watts to power the motor. If you need a battery to power the motor for 3 hours, then the battery must have a capacity of at least 18 watts * 3 hours = 54 watt hours.
Everyone’s answers are correct but they miss the point of why kW are confusing.
It’s confusing because kW is a rate, and we are used to rates being expressed in units per time. Dollars per hour. Miles per hour. The multiple the rate by the amount of time the rate applies for and you get the total quantity of dollars paid or miles traveled.
kW is a rate but the ‘per time’ is built in.
kW are “kWh per hour”.
The difference is between power and energy. It’s more intuitive to use a mechanical example to explain them:
Energy (KWh or Joules) is the total amount of force used to accelerate an object to a particular speed over a particular distance. E.g. The energy used to push a barrel up a hill.
Power (KW or horsepower) is the rate at which that force can be applied to get the object to a particular speed. E.g. Whether you are pushing the barrel up the hill quickly or slowly.
The energy used to push the barrel up the hill is the same whether it took you 5 mins or 5 hours. The rate of work (the power) is different.
To apply it to the electricity bill, you dont pay more if you use electricity quickly for 5 mins or slowly for 5 hours, they are interested in how much electrical energy you used in total when charging you.
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