New to solar

Tman

Hello,I'm very new to Solar. I currently have the harbor freight solar set up which no longer works for what we need trying to use 2 12v batteries.It obviously will not recharge the batteries.My question is how many panels do I need to be able to charge 2 12v 100 amp batteries.We will be running 10 12 volt led light bulbs which I believe are 10 watts a piece and 2 12 volt water pumps for running water to a sink and to a shower.also is the 30 amp charge control good enough.

BB.

Welcome to the forum Tman... I will show you the math that I would suggest to follow.

1. Figure out the daily loads.

Making lots of guesses here, but fairly conservative values:

10 LEDs * 10 Watts per bulb * 5 hours per night = 500 Watt*hours per day LEDs
2 pumps * 8 amps per pump * 12 VDC pumps * 1/3rd of an hour (20 minutes per pump per day) = 64 WH per day pumping
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564 WH per day average loads

Note that even though each pump is (8 amps * 12 volts) 96 Watts, they usually do not run very long. Note a water pressure tank may save energy too (pump water to tank only when make up water is needed vs running the pump 20 minutes for a full shower, as an example).

The 100 Watts of LED for 5 hours per day is the vast majority of the loads... Using 5 Watt bulbs, only running a few at a time rather than all 10 at once will save quite a bit of energy.

Again, these are probably worst case estimates...

Next, size the battery bank... Typically 2 days of storage (bad weather) and 50% max discharge for longer battery life:

564 WH per day * 2 days storage * 1/0.50 max discharge = 2,256 WH of storage (2 days plus 50% reserve)
2,256 WH / 12 volt battery bank = 188 AH @ 12 volt battery bank

To move things forward, guess that you 2 x 100 AH @ 12 volt batteries for 200 AH @ 12 volt battery bank as a good start.

Next, sizing the solar array... You did not say if these was a 12 month a year power usage, emergency backup, or weekend cabin. For now, lets size for 12 months a year, and minimum backup Genset usage (mostly solar).

Guess you are around Springfield Missouri, solar array facing south, tilted to 37 degrees from horizontal (best average year round harvest). Using PV Watts to estimate "hours of sun per day by month":

https://pvwatts.nrel.gov/pvwatts.php


Let's pick December at 3.51 hours of sun per day (winter). The size of the array would be:

564 WattHours per day * 1/0.77 panel+controller efficiency * 1/0.80 Flooded Cell Lead Acid battery eff * 1/3.51 hours of winter sun per day average = 261 Watt array "winter" break even...

Of course, the 3.51 hours per day are 20 year average December sun... Suggest that you only use 50% to 65% of predicted sun per day for bad weather and to minimize Genset usage. For example:

261 Watt array / 0.50 solar panel fudge factor = 522 Watt array to minimize Genset usage during winter

Now, we should also size the array based on solar charging current and battery bank size... Typically suggest 5% minimum rate of charge (emergency backup system), 10% for a "daily use" solar system, and 13% or higher to keep the cycling battery bank "happier". Using 200 AH @ 12 volt battery bank:

200 AH * 14.75 volts charging * 1/0.77 solar panel+controller deratings * 0.05 minimum rate of charge = 192 Watt array "minimum"
200 AH * 14.75 volts charging * 1/0.77 solar panel+controller deratings * 0.10 nominal rate of charge = 383 Watt array "nominal"
200 AH * 14.75 volts charging * 1/0.77 solar panel+controller deratings * 0.13 healthy rate of charge = 498 Wawtt array "healthy"

So an array in the range 383 Watts to 498+ Watts would be "justifiable" for my mythical full time usage system guesses above.

Your thoughts?

-Bill