Posted by Just_a_fan on March 10, 2008, 9:14 pm
On Mon, 3 Mar 2008 23:27:17 -0000, in alt.solar.photovoltaic "David
You are almost there. You must mean 14 kilowatt-days since you made 14
KW in a way. In that case, the hours have nothing to do with it.
Except there in NO NEED for either time unit after the fact. You
produced 14 kilowatts. Whether it was in an hour or a day, once it is
done, it is 14 kilowatts. That's all that is needed.
If you produced 14 kilowatts in a day, then that's great but then the
hours term is irrelevant. And once the day is done. the hours term is
particularly useless. Then it becomes 14 kw-day.
It is completely absurd to have two time elements on one quantity. Where
else would you find this?
I drive 60 miles per hour per day? Also meaningless. Did I drive 60
miles per hour or 60 miles per day? I could have driven 60 miles per
hour or 1440 miles per day. Or I could have driven a total of 60 miles
in a day. Having two different time units on single quantity (miles, in
this case) makes it makes no sense.
Once you get to a place, if you got there in an hour and it was 60
miles, you drove at a rate of 60 mph (notice "rate" here). But when you
arrive, you have driven 60 miles (quantity). It does not make any
difference to your car whether you did it in an hour or a day. You car
went 60 miles. The difference is talking quantity and rate. Once done,
rate does not matter. You drive 60 miles. You used 60 miles worth of
gasoline. The gas gauge does not care if you used it in an hour or a
day. You used that much energy and that's what you pay for at the pump.
The gas pump does not care if you used the tank full in an hour or a day
or a month. It is a quantity of energy you purchase. Just like a watt
or kilowatt. It is a quantity of energy independent of time element.
I guess I have to give up. It seems that one or two of you cannot see
the difference of quantity and rate and demand to put two different rate
units on a single quantity and believe this to be correct.
I give up. Go blindly with this absurd naming. I thought I would find
intelligence in this group. Sorry, I was wrong.
Posted by David French on March 10, 2008, 11:34 pm
Erm - NO, you really don't get it, do you! You can't change your time
reference without correcting the power proportionately!
Think of a small 1.5V re-chargeable battery, say 600 mA Hours....
Theoretically it can provide 600mA for ONE Hour. If you reduce the
current to 60mA, it will supply this current for TEN Hours, but the
total is STILL 600mA Hours. Whether you use it over one comtinuous
period, or several short periods over a month, the TOTAL is always
going to be 600mA Hours - not 600mA 'Days' or 'Weeks'!
14 Kilowatt-hours means that you can produce a Kilowatt for 14 Hours.
14 'Kilowatt-days' equals 336 kilowatt-hours, (24Hrs*14Days*1kW)
which is wrong because you have changed your time reference without
correcting the power drawn over that period of time, in proportion!
You totally missed the point again... time IS absolutely relevant when
calculating total energy in kWH - that's what the 'H' is there for!
You don't buy energy in watts or kilowatts.... you buy it in
Has the penny dropped yet?
You forget that it doesn't take you ALL DAY to travel the 60 miles!!!
That is why you don't call it 60 Mile-Days - it is just 60 Miles, full stop.
Also, if you travel 60 miles in one hour, once you get where you are going
there is no more energy used for the rest of the day, so according to your
method the total will remain at 60 miles of travel no matter how long you
continue to measure it for the rest of that day - get it ?? So for the
23 hours time has no relevance in the calculation because you are not
It doesn't matter how long you take to travel the 60 miles, because it would
a perfect car) take the same energy to travel 60 miles in one hour at 60 MPH
as it would take to travel 60 miles in 10 hours, at just 6 MPH.
What we are saying is correct - and all covered by basic physics.
I suggest you read a few books from the library on physics and the
measurement of energy (SI Units).
The intelligence is here, but 'there are none so blind as those who will
Posted by rlsusenet@NOSPAMPUHLEEZschnapp on March 10, 2008, 11:49 pm
I hesitate to wade into this nonsense, but what the heck?
Mike, there's absolutely nothing wrong with citing the number of
kilowatt-hours per day a particular installation generates.
A kilowatt-hour is a unit of energy. kWH/day is the amount of energy
generated per day. kWH is the most commonly cited unit of energy for
Yes, if you like, you could cite kilowatt-days (14 kWH per day == 14/24
kWD = 0.58 kWD), but nobody relates to that because nobody has ever seen
a bill in kWD.
Thus, it is perfectly sensible to discuss kWH per day. Feel free to
discuss kWD if you prefer, but get the arithmetic right, and be prepared
to be giggled at, a little bit.
Posted by Solar Flare on March 11, 2008, 2:06 am
I drive up to 120 mph and I average 60mph per each hour driven.
Posted by bealiba on March 11, 2008, 8:21 pm
Kilowatt-hour, Symbol: kWh. A unit of work or energy defined as the
energy produced when one kilowatt of power is expended for one hour.
For the subject of system sizing it is generally accepted that kWhs is
for a period of a day. For the use of the power company it could be
for a month or quarter or even yearly.
To say "X kWhs per day" is quite correct but more often than not is
just stating the accepted norm, whereas, kWhs per week/month/year is
more specific about use over a period.
A kilowatt on the other hand is 1000 Watts.