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Q & A: Watts vs kWh

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Most recent answer: 03/28/2010
Explains the difference between 2400 W and 3kWh
- Cori Barrera (age 15)
Watts are a unit of power, and kilowatt-hours are a unit of energy. Power is a measure of energy per unit time, and a watt measures how many joules (the standard international unit of energy) of work can be done in one second. A kilowatt-hour is the amount of energy corresponding to the work that can be done with a one kilowatt (one thousand watt) source of power operating for one hour (which is equal to 3.6 million joules). The reason for the different units of energy is that a kilowatt-hour is much larger than a joule and is more convenient in some situations. Hope this helps!


(published on 10/22/2007)

Follow-Up #1: 50,000 Watts and 50 kwh

How many watts in 50 kwh? Is 50,000 watts the correct answer?
- Al Bowers (age 36)
Eden Prairie, MN, USA
There are two conversions going on here.   One is that the  letter  k in kwh stands for kilo or 1,000.      So there are 50,000 wh in one kwh.      The other is that the h in kwh stands for hour.    A Watt is a rate of using energy.    A Watt-hour is an amount of energy.   You pay the electric company for the amount of kwh you use.  


(published on 08/01/2008)

Follow-Up #2: windmill power

Okay, So I am looking at buying a windmill that produces 500 KWH per month at a rate of 12 mph. How many watts does that come out to be per month?
- Steven Clark (age 20)
Actually, you already know how much energy your windmill produces per month (under these conditions): 500kWh. Watts (and kilowatts) are units of power, energy per time. When you multiply by a time (say one hour) you get units of energy, such as kWh.

What you can figure out is how much power you typically get, in Watts. If you get 500 kWh/month that's 500kWh/(24*30 h/month). (I'm using 30 day months.) That's 500/720 kW, or about 0.7 kW= 700W.

Mike W.

(published on 03/28/2010)

Follow-up on this answer.