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How many panels ? ( to run 230 volt sprinkler pump 30 minutes a day?) - Page 50

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Posted by Ron Rosenfeld on July 18, 2008, 1:56 am
 
On Thu, 17 Jul 2008 16:47:50 -0700 (PDT), bealiba@gmail.com wrote:


No, George.  The "truth" is that YOU have put certain specifications into
your spreadsheet which are impossible to reconcile with a useable system.

The "truth" is that you got yourself involved with battery storage, and
then just dug yourself into a deeper and deeper hole when you did it wrong.

The "truth" is that you were more interested in finding some way to
criticize my 10 panel recommendation as being oversized (even when all of
YOUR recommended systems were larger!) than you were in devising a useful
system.

The "truth is that you specified the PV panels using a voltage/current/NOCT
combination that NO manufacturer uses for panels designed to work in a 12V
system.

The user did not input:

B2      Maximum allowable depth of discharge = 70%
B13     Capacity of battery bank at 100 hr rate (B12 x B10) = 180
C4     Battery efficiency = 90%

*YOU* input that data.  No one else did.

And, when challenged, you wrote that the data was correct!

That data will not result in a working system.

Since you haven't been able to comprehend that, let me lay it out for you:

You cannot produce a real-world battery with a capacity of 180Ah at the 100
hr rate, that will have a capacity sufficient to run this pump for 30
minutes.

Why?

We both agree that the pump requires 122.5Ah to run for 1/2 hour. Therefore
it will be drawing 245A during that 1/2 hour.  (245/22.5)

Deep-cycle lead acid batteries have a significantly lower capacity at
higher current draws.  How much lower depends on the specific battery.  So
a T105 which might have a capacity of 240 Ah at the 100 hr rate, when you
are drawing 2.4A, will only have a capacity of 56 Ah, when the pump is
running and drawing 245A.  And of that 56 Ah, since the DOD is limited, you
can only withdraw 40Ah.  It won't even run for 1/2 hr!  That leaves a
significant shortfall of 122.5-40 or 82.5 Ah!

If you specify a different battery, with a flatter curve, you might have a
30 minute capacity of perhaps 50% of the 100 hr rate.  But 50% of *YOUR*
180Ah specification is 90Ah.  That multiplied by your allowable DOD leaves
63Ah -- again a significant shortfall.

And it's made even worse than that, because in the above calculations, we
haven't even taken into account the discharge efficiency.  I'm not sure,
because you haven't specified, whether the 90% efficiency YOU input is
round-trip or discharge efficiency.  But it's going to decrease the
available amount regardless.

And it gets even worse because this is only on the first cloudy day.  Again
*YOU* specified 1 day of autonomy in your formula in order to come up with
YOUR recommendation of 180Ah at 100 hr rate.  No one else put those inputs
into your spreadsheet.

The same problem occurs in trying to fit YOUR input of a panel
specification into something that will work.  There's nothing produced for
a 12V nominal system that is rated at 14V 2.94A at NOCT and 17V with no
load.  Nobody other than YOU put that information into YOUR spreadsheet.
--ron

Posted by bealiba on July 18, 2008, 5:59 am
 

Change them to the specs for the equipment you choose to use. This is
the meaning of user input.

Your ten panels will not run the pump without batteries and you were
quite insistent that batteries not be mentioned.

Change it to the specs for the panel you have chosen. That is why it
is user input.

Don't like it change it. You are the user in this case.

The data is correct for the amount if information received from the
OP. i.e. Minimum battery capacity is 180Ah.

User input required required for further calculations to be made.

Because the 180Ahs is the minimum battery capacity required, not a
recommendation for a battery.

This is true. So change the battery specs.

User input. Change it to suit your choice of battery. Just how thick
are you?

The 180 Ah minimum battery capacity will be the same if you change to
the 0.5Hr discharge rate.

Tweedledee, the information that  is user changeable is just that. So
Change it. It's not that hard, pick a panel and put the specs in.


Posted by Ron Rosenfeld on July 18, 2008, 11:30 am
 On Thu, 17 Jul 2008 22:59:04 -0700 (PDT), bealiba@gmail.com wrote:



GG: Change them to the specs for the equipment you choose to use. This is
the meaning of user input.

GG: Change it to the specs for the panel you have chosen. That is why it
is user input.

GG: Don't like it change it. You are the user in this case.

GG: User input required required for further calculations to be made.

GG: User input. Change it to suit your choice of battery. Just how thick
are you?


GG: Tweedledee, the information that  is user changeable is just that. So
Change it. It's not that hard, pick a panel and put the specs in.

====================================================================

In other words, George, your vaunted specifications, which you have
insisted are correct, are just so much BS.

You rely totally on the user to provide specifications for equipment to be
used in his systems, and the guidance you give him is worthless.

I guess that's only to be expected <sigh>.
--ron

Posted by bealiba on July 18, 2008, 12:36 pm
 
One more time, The 180Ah is the minimum battery capacity required.
Even if the time rate is C0.5.

No. The specifications for equipment chosen for use has to be added to
the formula to get a correct answer. The calculations are a different
matter and should not be changed.


Well, yes. This is the basis of custom design, that the design should
meet the needs of the designer. This can only be achieved if the
specifications of the equipment are appropriate to the specified
task.


On no. Absolutely not. The guidance I have given here is the formula,
which is correct. Specifications for equipment to be used is to be
supplied by the user. One size does not fit all in the world of solar
power design.

Anyone can do it, well, with the exception of Tweedledee and
Tweedledum. As has been proven. If a person does not want the
responsibility of looking up the specifications required to size their
own system then they, quite plainly, are not prepared to be in a
position of supplying their own energy.


Posted by wmbjkREMOVE on July 18, 2008, 2:01 pm
 On Thu, 17 Jul 2008 22:59:04 -0700 (PDT), bealiba@gmail.com wrote:



LOL  This is the first time *ever* that I've seen you admit to the
effect of high-current loads on battery capacity. Now you're
pretending to understand, yet have forgotten <chuckle> to explain your
reason for inputting values which you knew <snorf> were completely
wrong.

"Who would hire this PV nitwit" - Nick Pine

Wayne

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