Finally System is done

Zakarume

My system is done. Last Night i drain the batteries down to a 75% SOC by what the Midnite Kid said along with Whizbang Jr. Today had full sun and it charge my bateries to full. What i would now like to do is add more to my system

1. Have 4 6v batteries in series for a 24v system (225AH).

2.Would like to add 4 more 6v batteries (8 total @450AH) PLUS

3. Take the 4 -100 watt panels i did have and reinstall in series/parellel for 24v and get a PWM Charge Controller for the extra charging of the 8 batteries.

Will this work at charging the 8 6v bateries at 450AH?

BB.

Re: Finally System is done

Total Wattage--Assuming 5% to 13% rate of charge:

• 450 AH * 29 volts charging * 1/0.77 rate of charge * 0.05 rate of charge = 843 Watt array minimum
• 450 AH * 29 volts charging * 1/0.77 rate of charge * 0.10 rate of charge = 1,695 Watt array nominal
• 450 AH * 29 volts charging * 1/0.77 rate of charge * 0.13 rate of charge = 2,203 Watt array "cost effective maximum"

You want to add 2x the battery bank and 400 Watt array to the existing:

• 960 Watt array + 400 Watt additional = 1,360 Watt array

You would be at:

• 1,360 Watt array / 1,695 Watt array (10%) = 0.8 or ~8% of battery capacity

That is a decent size array... But this depends on how you plan on using your power and how much.

If your daily power needs are mostly during the night--And, of course, you don't draw too much power, you should be fine.

If, however, you have significant power needs during the day (irrigation, office equipment, etc.) full time--Then you should look at your average wattage requirements for the loads--I.e., you want a 5% minimum into the battery bank + enough solar panels to support the loads (especially if this is a full time off grid system as opposed to backup/seasonal/weekend system).

Using PV Watts for Springfield Mo, 37 degree tilt from horizontal, fixed array:




Month
Solar Radiation
(kWh/m²/day)


1
3.93


2
4.20


3
5.18


4
5.54


5
5.71


6
5.80


7
5.92


8
5.99


9
5.44


10
4.95


11
3.83


12
3.29


Year
4.99




Toss the bottom three months (as needing backup genset or simply reducing power needs during poor weather):

• 1,360 Watt array * 4.2 Hours of Sun average per day (February) * 0.52 end to end system eff = 2,970 Watt*Hours per day of 120 VAC power

And, if your 100 watt panels have Vmp in the rang of ~17.5 to 18.6 volts or so, then two panels in series with two parallel strings connected to a PWM solar charge controller on a 24 volt battery bank should be fine.

-Bill