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

*>No correction is needed....*

*>'Kilowatt hours per day' makes perfect sense.*

*>If the wind blows for, say, 7 hours today, and your*

*>system generates an average of 2kW then you will*

*>produce a total of 14 Kilowatt hours of energy today.*

*>That is 14 Kilowatt Hours - in a 24 hour period (day).*

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.

Mike

*>OK?*

*>David.*

*>> One more correction in order.*

*>>*

*>> kw-hrs per day????????????*

*>>*

*>> What IS that?*

*>>*

*>> Killowatt hours per 24 hours?*

*>>*

*>> Does that make sense to anyone but you?*

*>>*

*>> Mike*

*>>*

*>> On Sun, 3 Feb 2008 17:10:08 -0800 (PST), in alt.solar.photovoltaic*

*>>*

*>>>*

*>>>*

*>>>In an earlier post I wrote as follows:*

*>>>*

*>>>"*

*>>>Wind power? Well let's see. At 2 Mw each one might expect to get not*

*>>>48 kw-hrs per day, but more like 10 kw-hrs per day. And how much*

*>>>energy do people consume? Well, according to the US DoE about 200 kw-*

*>>>hrs per day per person! That would suggest we would have to install*

*>>>about 20 wind generators per person. Ooooh look, that's only 13*

*>>>billion worldwide. Piece of cake, not."*

*>>>*

*>>>There is an error here. The correct version should read as follows:*

*>>>*

*>>>Wind power [which after all comes for solar energy]? Well let's see.*

*>>>At 2 Mw each one might expect to get not 48 Mw-hrs per day, but more*

*>>>like 10 Mw-hrs per day. And how much energy do people consume? Well,*

*>>>according to the US DoE about 200 kw-hrs per day per person! That*

*>>>would suggest we would have to install 1 wind generator for every 50*

*>>>people. Ooooh look, that's only 130,000,000 worldwide. Piece of cake,*

*>>>not.*

*>>>*

*>>>My apologies for any inconvenience this may have caused.*

*>>>*

*>>>GeorgeB*

*>> *

Posted by *David French* on March 10, 2008, 11:34 pm

*>>No correction is needed....*

*>>*

*>>'Kilowatt hours per day' makes perfect sense.*

*>>*

*>>If the wind blows for, say, 7 hours today, and your*

*>>system generates an average of 2kW then you will*

*>>produce a total of 14 Kilowatt hours of energy today.*

*>>*

*>>That is 14 Kilowatt Hours - in a 24 hour period (day).*

*>>*

*> 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.*

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!

*> 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?*

You totally missed the point again... time IS absolutely relevant when

calculating total energy in kWH - that's what the 'H' is there for!

*> 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.*

You don't buy energy in watts or kilowatts.... you buy it in

Kilowatt-HOURS!!!!

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

remaining

23 hours time has no relevance in the calculation because you are not

moving!

It doesn't matter how long you take to travel the 60 miles, because it would

(in

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.

*> 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.*

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).

*> I give up. Go blindly with this absurd naming. I thought I would find*

*> intelligence in this group. Sorry, I was wrong.*

The intelligence is here, but 'there are none so blind as those who will

not see'.

David.

Posted by *rlsusenet@NOSPAMPUHLEEZschnapp* on March 10, 2008, 11:49 pm

Just_a_fan@home.net wrote:

*> On Mon, 3 Mar 2008 23:27:17 -0000, in alt.solar.photovoltaic "David*

*> *

*>> No correction is needed....*

*>>*

*>> 'Kilowatt hours per day' makes perfect sense.*

*>>*

*>> If the wind blows for, say, 7 hours today, and your*

*>> system generates an average of 2kW then you will*

*>> produce a total of 14 Kilowatt hours of energy today.*

*>>*

*>> That is 14 Kilowatt Hours - in a 24 hour period (day).*

*>>*

*> 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.*

*> *

*> Mike*

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

retail purposes.

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

wrote:

*> No correction is needed....*

*> 'Kilowatt hours per day' makes perfect sense.*

*> If the wind blows for, say, 7 hours today, and your*

*> system generates an average of 2kW then you will*

*> produce a total of 14 Kilowatt hours of energy today.*

*> That is 14 Kilowatt Hours - in a 24 hour period (day).*

*> OK?*

*> David.*

*> > One more correction in order.*

*> > kw-hrs per day????????????*

*> > What IS that?*

*> > Killowatt hours per 24 hours?*

*> > Does that make sense to anyone but you?*

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.

>No correction is needed....>'Kilowatt hours per day' makes perfect sense.>If the wind blows for, say, 7 hours today, and your>system generates an average of 2kW then you will>produce a total of 14 Kilowatt hours of energy today.>That is 14 Kilowatt Hours - in a 24 hour period (day).