Installing Off-Site Watering Setup

[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]

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]

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]

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

[Sunking]

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

[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?