Solar charging series or parallel for MPPT to 12v battery

Ignoring Solar for the moment...

[note: I messed up here--25 feet and 12 watts--See following post for corrections]

That battery seems awfully small for your application (12 volt @ 34 Amp*Hours??):

• 12 volts * 34 AH * 1/25 watt load = 16.3 hours until "dead"

If you want to go 2 days without sun and 50% maximum discharge (for longer battery cycle life):

• 25 watts * 24 hours per day * 1/12 volt battery bank * 2 days * 1/0.50 maximum discharge = 200 Amp*Hour @ 12 volt battery bank

You may want to look at using 2x 6 volt @ ~200 AH golf cart batteries--At least for the first try. They may be a lot cheaper and easier to monitor (can use a hydrometer, add distilled water once a month). Once you get the system stable and working the way you want--Eventually replace with AGM (more expensive, less maintenance, perhaps a bit shorter cycle life).

-Bill

I would suggest placing all serviceable components at the base of the pole--Unless you have easy/cheap access to a lift.

Of course, that gets security questions (if a problem). Possibly place the electrical box at a lower height (use a ladder).

And "Oops...". I got my numbers mixed up, you are running 12 Watts, not 25 watts--Mixed the numbers up in my earlier post:

• 12 volts * 34 AH * 1/12 watt load = 34 hours until "dead"
• 12 watts * 24 hours per day * 1/12 volt battery bank * 2 days * 1/0.50 maximum discharge = 96 Amp*Hour @ 12 volt battery bank

Sorry.

• 12 watts * 24 hours per day * 1/0.77 charge controller+panel derating * 1/0.90 AGM batt eff * 1/2 hours of sun per day = 208 Watt array minimum
• 96 AH battery bank * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 181 Watt array recommended minimum size (10% rate of charge)

So, a pair of ~100 Watt panels would appear to fit the minimum requirements.

You started this as a wiring length question--Solar panels mounted on pole? And yes, I probably would use the two solar panels in series to allow a smaller awg wire. Using a generic voltage drop calculator:

• 2 * 100 Watt panels * 1/35 volts Vmp-array = ~5.71 amps Imp

http://www.calculator.net/voltage-drop-calculator.html for 3% to ~1% maximum drop

• 0.03 maximum recommended voltage drop * 35 volts Vmp-array = 1.05 volt maximum drop

Using voltage drop calculator with 25 feet one way run and 5.71 amps and 1.05 maximum voltage drop:

14 AWG wire:
Voltage drop: 0.72
Voltage drop percentage: 2.06%
Voltage at the end: 34.28

10 AWG wire:
Voltage drop: 0.29
Voltage drop percentage: 0.83%
Voltage at the end: 34.71

So, I would suggest around 14-10 AWG wire as being optimum for this installation.

-Bill