Installing Off-Site Watering Setup

[OregonSolar]

EQ charge on average is once a month and weekly watering.

OK, since this setup preferably needs to be checked at least every other day anyway, the watering is not an issue. Is a 200 watt charge current (8A) enough to cause the necessary roiling? 'Cause the panel should on average be putting that into the batteries for about 2hrs a day.

Again, if it's only monthly a person can just go out and, say, connect jumper cables from a truck to each battery in turn for a minute? Since the system is 24V, each battery can be done separately by temporarily disconnecting them. Is a minute of 20-30A charge current per battery enough?

And does testing the specific gravity require a tester or something? something that I can grab for $50 or less to include with the system?

[Sunking]

EQ charge on average is once a month and weekly watering.

[Naptown]

If you maintain a bit of bubbling ( not boiling) it will be very infrequent
In your case perhaps once a month or less depending on what the specific gravity tells you

[OregonSolar]

The stickie takes into account what it takes to replace what you use daily.
It also takes into account the max charge rates for batteries not the minimum.
Off grid people also have and it is required for long periods of rain to have a generator and charger.
This will allow a periodic equalization charge to stir up the electrolyte in the batteries.
You will need to have some way of charging batteries other than solar to account for extended cloudy weather and to perform a
Periodic equalization charge or the batteries will stratify.
One way around this is to use AGM batteries. Which do not stratify.
I will add something to the calculator to account for minimum charge rates when I get some time.

Well, I'm not sure I could justify the added cost and reduced longevity of AGM batteries. I understand the stratification phenomenon. But this system is ideally supposed to be able to be placed out in a remote field for 6 months with minimum maintenance beyond checking to make sure it is pumping the water and keeping up with the cows. How long on average does an equalization charge last? I mean, is something that someone could go out in the field, do manually for 15-20 minutes and be good for the week or more? And could you do this by say, running a cable from a running truck's battery and a controller to the solar batteries?

Assuming you had enough solar power available, could you not also do this equalization with solar panels?

[Naptown]

The stickie takes into account what it takes to replace what you use daily.
It also takes into account the max charge rates for batteries not the minimum.
Off grid people also have and it is required for long periods of rain to have a generator and charger.
This will allow a periodic equalization charge to stir up the electrolyte in the batteries.
You will need to have some way of charging batteries other than solar to account for extended cloudy weather and to perform a
Periodic equalization charge or the batteries will stratify.
One way around this is to use AGM batteries. Which do not stratify.
I will add something to the calculator to account for minimum charge rates when I get some time.

[OregonSolar]

Now here is where the pwm vs mppt part comes in
In your case that 240w panel at 36v
Will produce about 5 amps
With PWM amperage in= amperage out so with a pwm controller you have a charge current of about 5 amps
Now move to an mppt and things get different
Watts in = Watts out - about 5%
So 240 watts in = 240 watts out - 5% = about 228 watts out
228/24 is just under 10 amps
Enough to keep a 100ah battery very happy

Will keep a 100Ah battery happy, but what about a 200Ah? According to the calculator stickie, i'll need a 240 watt panel 24V on an MPPT charge controller with a 200Ah battery. I assume I'll be on the lower end of the battery charging scale?

[Naptown]

Now here is where the pwm vs mppt part comes in
In your case that 240w panel at 36v
Will produce about 5 amps
With PWM amperage in= amperage out so with a pwm controller you have a charge current of about 5 amps
Now move to an mppt and things get different
Watts in = Watts out - about 5%
So 240 watts in = 240 watts out - 5% = about 228 watts out
228/24 is just under 10 amps
Enough to keep a 100ah battery very happy

[Sunking]

The panel I'm looking at says a Vmp of 36V. Even though it is marketed as a 24V panel. Time to change...

That is a 24 volt battery panel. 12 volt solar panels are 36 cells in series with a Vmp = 18 volts. 24 volt battery panels are 72 cells operating at 36 volts and can also be used as Grid Tied. 30 volts is not quite enough for a 24 volt battery system.

OK your panel with PWM will generate 160 to 170 watts at the battery. Same panel with MPPT up to 230 watts.

[OregonSolar]

No a 24 v panel will put out about 36 volts.
Battery voltage x 1.5

Makes sense now. So a 36V system (however odd and wierd) would require about a 48V panel setup, so on and so forth.

Understanding Dawns!
Sothe panel I already have picked out will be Perfect.

[Naptown]

OK, I see now.

A panel need a certain amount of head voltage to charge a battery. So a 24V grid-tie panel might only put out 25 or 26 volts while a battery panel will putout 30 volts, which is enough to actually put some current into the battery.

So it's kind of like trying to fill a tire to 40PSI with a compressor that's only putting out 50. You'll eventually get the tire full, but it's going to take a looooooongtime when it starts to get near full.

No a 24 v panel will put out about 36 volts.
Battery voltage x 1.5

[Naptown]

Most of the 200-270 w panels are going to be 60 cell
Once you get to 300 with a few exceptions they will be 72

[OregonSolar]

Cell count is directly proportionate to voltage. With the exception of amorphous panels.
Generally a single cell will produce .5 volts at max power and .6 volts open circuit.
Doesn't matter how big the cell is a 1"
Cell will be the same voltage as a 6" cell however the amps and watts will differ

OK, I see now.

A panel need a certain amount of head voltage to charge a battery. So a 24V grid-tie panel might only put out 25 or 26 volts while a battery panel will putout 30 volts, which is enough to actually put some current into the battery.

So it's kind of like trying to fill a tire to 40PSI with a compressor that's only putting out 50. You'll eventually get the tire full, but it's going to take a looooooongtime when it starts to get near full.

The panel I'm looking at says a Vmp of 36V. Even though it is marketed as a 24V panel. Time to change...

[SunEagle]

What relation does the cell count have? Does it really matter?

Already decided: changing to a MPPT.

The more cells you put into a series circuit the higher the max power output voltage of the panel. A 36 cell panel usually yields about 18 Vmp. A 72 cell panel yields about 36 Vmp. A 36 cell panel is called a battery panel. A 60 or 72 cell panel is called grid tie.

[Naptown]

Cell count is directly proportionate to voltage. With the exception of amorphous panels.
Generally a single cell will produce .5 volts at max power and .6 volts open circuit.
Doesn't matter how big the cell is a 1"
Cell will be the same voltage as a 6" cell however the amps and watts will differ

[OregonSolar]

Panels made for batteries generally will have a cell count of 36 for 12v and 72 cells for 24v
That said there are a lot of 72cell grid tie panels out there.
However you are still losing a good bit with a PWM controller. Roughly a third
You will need a minimum of 72 cells to charge a 24v battery efficiently.

What relation does the cell count have? Does it really matter?

Already decided: changing to a MPPT.