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Watt vs kilowatt.hour 
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#1
Nov2712, 01:25 AM

P: 5

Hello,
getting confused about watt vs watt.hour in the Watt's wiki page, an example is given on how to calculate wattage (power): this system needs aroud 600 watts of power to accomplish its task. ok. Then, lower in the page, an example is given on how to calculate watt.hour(energy): Now, if I go back to my first example, it's being done in 5 seconds for 588,6 watts if it was done in 1 second, it would be 2943 watts if it was done in 3600 seconds, it would be 0,8175 watts So, if I do the work on a 1 hour (3600 sec) time span, can say I use 0,8175 watt.hour? And if I lift the thing in 1 second, but constantly, for 1 hour, do I use 2943 watt.hour? This is confusing me a little, so I guess my question also is a little confused. I looked many places where it was promised that this confusion would evaporate after reading their explanations. Now I'm here because I'm still a little lost. thanks 


#2
Nov2712, 02:47 AM

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Thanks
PF Gold
P: 12,157

It may help to ignore the actual figures for a start. The Watt is a unit of Power  the rate of doing work or using energy. The kW hour is a unit of Energy  just like the more basic Joule. If you read each problem / example carefully you will always see whether Power or Energy is what is needed.
Power is Energy / Time Energy is Power X Time Hold that in your head and the numbers will look after themselves. 


#3
Nov2712, 05:35 AM

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P: 22,294

Your confusion isn't affecting your ability to do the math, so I'm not sure what there is we can do to help other than to tell you to trust your understanding, because you understand correctly. ...Or ask us another question... 


#4
Nov2712, 06:37 AM

P: 14

Watt vs kilowatt.hour
NO need to confuse over it. Just Take it easy. I try to make it clear.
Actually the rate of work done is called power. I mean for calculating the power you must know the work done. ... Work done per sec is called power and measured in Watt. Work done per minute is also power. Work done per hour is also power but measured in Watt.hour. Actually Watthour And killowatthour is represent the power produce by a machine in 1 hour. Suppose a machine produce 1500watt power in one sec. then it will produce 1500X60 watt in a minute and 1500x60x60 in a hour or i can say 1500x60x60/100 Kwatthour (KWH) hope you understand thanks 


#5
Nov2712, 06:51 AM

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PF Gold
P: 12,157

Yep. Two issues here. 1. Believe the Physics. 2. Believe the arithmetic.



#6
Nov2712, 08:19 AM

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#7
Nov2712, 10:12 AM

P: 1,969

A watthour represents a specific amount of energy (3600 J) no matter in what time is this energy used or transformed. Even saying "power produced in 1 hour" is meaningless. The machine "produces" energy. Power shows you how fast is done, not necessarily how much of it. 1 watt hour of energy may be "produced" in 1 second or 1 billion years. It's still 1watthour. 


#8
Nov2712, 12:11 PM

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PF Gold
P: 12,157

I find people's determination to use the wrong terms, in this way, very annoying. It's as if they really don't get it. People who get aerated about the 'offside rule', as if it's actually important. But they will use scientific terms interchangeably like some poet who can't bring himself to use the same word twice in a sentence and scrabbles around to find a shoddy equivalent. The fact is that there is, with very few exceptions, only one word for each scientific concept. It just does not help anyone to have the alternative (wrong) terms used instead. It doesn't make the subject any more approachable  just the reverse. I heard some clown of an energy minister on BBC Radio, recently, talking about "storing Power"!!! What hope do we have? 


#9
Nov2712, 12:50 PM

P: 1,969

In common language, power is used so often for "energy" that maybe you should close you eyes. It's a "power station" or "power plant" after all. At least in North America. A car factory produces cars which are stored in parking lots. So what does a power plant produce (and store)? 


#10
Nov2712, 01:07 PM

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PF Gold
P: 12,157

I clearly made the mistake of hoping that he should know what he's talking about.
If he's as ignorant as that, how can he distinguish between sense and nonsense when he's being sold some idea by a flash salesman? The distinction could be highly relevant to making a good decision. For instance, what use is a 5MW wind turbine if it only operates for 30 days per year? (You wouldn't be confused, by common language, yourself would you??? ) 


#11
Nov2712, 01:33 PM

Sci Advisor
P: 2,470

:p 


#12
Nov2712, 03:02 PM

P: 1,969

This makes some difference. 


#13
Nov2712, 03:05 PM

P: 1,969




#14
Nov2712, 03:23 PM

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PF Gold
P: 12,157




#15
Nov2712, 03:25 PM

Sci Advisor
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PF Gold
P: 12,157

Not sure you could actually fit a 5MW turbine on your roof. I was thinking more of those big devils out at sea. They are owned and run by the Elec company. Did you consider the capital cost of one that big? 


#16
Nov2712, 03:32 PM

P: 588

Kuin,
Here is an analogy for you. The bottled water factory produces 8,000 gallons per day. I can store 10 gallons in my pantry. See the difference between "gallons per day" and "gallons"? 


#17
Nov2712, 03:34 PM

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PF Gold
P: 12,157




#18
Nov2712, 04:42 PM

P: 3,143

A lot of the confusion comes because the energy companies use kWh as a measure of energy which it is (because its power * time) but it's not a basic unit like the joule. To make matters worse you sometimes find people talking about "kWh per hour" which is the same as saying kW.



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