Check my math

As always, refer to the manual for safety limits (voltage, current, etc.)...

Just a quick set of math for sizing the array... Nominally, for an off grid system suggest 10-13% rate of charge, and upwards of 20% for areas with "dark" winters (I.e., not much sun, so over paneling does not "waste" much energy with an XX Amp controller)(Note: 300 AH @ 12 volt battery bank assumed):

• 300 AH battery bank * 14.5 volts nominal charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 565 Watt array minimum suggested off grid array
• 300 AH battery bank * 14.5 volts nominal charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 734 Watt array (more or less optimum for Lead Acid Battery banks)
• 300 AH battery bank * 14.5 volts nominal charging * 1/0.77 panel+controller derating * 0.20 rate of charge = 1,130 Watt array suggested maximum for 300AH @ 12 volt battery bank

Note that 1,200 Watts is "close enough" for 1,130 Watt array "solar math".

For a 60 amp MPPT controller... The maximum "most efficient" solar array for a 12 volt battery bank would be:

• 60 Amps * 1/0.77 panel+controller deratings * 14.5 Volts charging = 1,130 Watt array "typical" cost effective maximum array for 60 amp MPPT controller on a 12 volt battery bank

Again, solar math is "fuzzy math"... More or less, a 1,130 Watt array may "safely and reliably" clip the charging current to 60 Amps a few hours a year on a cool/clear day near solar noon... A larger array will simple "clip" more hours (waste energy) more often... But perfectly OK to "over panel" a system in a "dark winter" location. During summer, you will have "lots of harvested" energy.

Just for a quick summary of some other quick rules of thumbs... Normally would suggest that a battery bank is sized to deliver 1/4 of its storage capacity per day (i.e., 2 days of "no sun" stored energy, to 50% planned state of charge--And on rare occasions to 20% state of charge).

So, for a 300 AH @ 12 volt battery bank:

• 300 AH * 0.25 discharge = 75 AH per day (or over night) discharge
• 75 AH * 12 volts * 0.85 AC inverter eff = 765 Watt*Hours per day/night discharge

And to calculate the hours of sun per day by month (assuming no trees/mountains blocking sun part of the year). Guessing Munising Mi, 47 degree from horizontal fixed array facing south (using 1,000 Watt array as starting point for software):
https://pvwatts.nrel.gov/pvwatts.php


Worst case December with 1.85 hours of sun (not much) and a 1,200 Watt array (a little more clipping on cool/clear days):

• 1,200 Watt array * 0.77 panel+controller derating * 1.85 hours of average Dec Sun = 1,709 WH per average December day (or a little less in December and "over paneled")

For the array--With an MPPT controller, this "class" of solar controller will typically have a maximum solar array input voltage of 100-150 Voc-cold (check manual, ask more questions if needed).

Need to have the exact specifications for your 200 Watt panels... Voc/Vmp/Isc/Imp... You would typically put 2 or 3 panels in series (check Voc-cold for your panels) and parallel the strings (2s*3p or 3p*2s)... 2s*3p would work with almost any solar panels and charge controller.

If you have three or more parallel strings, you are supposed to used a "Combiner Box" with fuses or circuit breakers (help reduce the chance of fire if one panel/wire run becomes shorted)... If you can go with 2s*3p, you can save the price of a combiner box.

Lots of details to work out--In general, size the battery bank to your loads, and size the solar array to your battery/loads/hours of sun. And in the "far north", a Genset, possibly a wind turbine (lots of issues), etc. are usually needed for those dark/stormy days...

-Bill