Battery Calculation

[Jeff From NJ]

I'm trying to figure out the number of batteries to purchase to make my new system operate. Currently, I have 6 panels running in a 2S3P setup (260W, 30.6V, 8.5A). I currently have two 12V 100MAh LiFePO4 batteries that I will combine to get 24V and was thinking I should grab another two, making 4 batteries at 24V 100MAh.

At 12V, the batteries appear to give 1280Wh each, so I am thinking if I had 4, I would have 1280 x 4 or 5120Wh and based on my power estimate below, I need 4058.6WH to run the house.

I'm not sure if connection the 4 batteries together to get 24V 100MAh will give me the 1280Wh per battery and I am not sure if it does if it is enough to power the house load. I am 90% certain I am messing up the calculations. Could someone step in and tell me how many 12V 100MAh batteries I would need to run the house.

Thanks all!

Battery Sizing
Daily Storage Requirement	1826	W-Hrs/Day
Max discharge from full CHARGE	90.0%	%
# days of storage capacity	2.0	Days
System Voltage	24.0	Volts
min Battery capacity W-Hrs	4058.8	W-Hrs.
min Battery capacity A-Hrs	169.1	Amp Hours
Max continuous current to DC Loads	7.3
Max continuous DC current to Inverter	84.7
Max continuous current from bat.	92.0	Amps
Max Continuous discharge rate	0.54	C
Solar Aray Sizing
# sunny days to recharge while under load	3.0	Days
Required Total daily Solar output (Sunny)	3044.1	W-Hrs.
Insolation # (Equivelent hours of full sun)	5.0	Hours
Min Solar Cell Wattage	608.8	Watts
Max Charge Current	25.4	Amps
Max Charge rate	0.15​	C

 

[Leeds]

I need 4058.6WH to run the house.

How exactly did you arrive at this figure? It seems suspiciously/unreasonably low.

You're proposal is a 2p2s battery bank that's a nominal 25.6V and 200 AH deep which as you noted would yield roughly 5120Wh.

In my area I use 4 equivalent hours of full production, you have noted 5 which may be possible at your location, it would be a stretch in mine.
Your panel size seems waaaaaaaay too small. You have exactly 260w total?

There's a lot more to comment on but understanding how you measured your current consumption to be 4 kwh a day is probably the most important thing to square away first.

 

[Jeff From NJ]

The panels EACH are 260W, 30.6V, 8.5A

 

[Leeds]

I need 4058.6WH to run the house.

Again, where did this number come from? If it's accurate and assuming you pay the average rate in NJ which I'm told is is 17.35 cents per kilowatt hour, your current on-grid electricity bill is roughly 72.4 pennies a day.

If you currently pay more than about $21 per month in electricity then you need to fix that number before you can work out how large a system would satisfy it.

 

[Supervstech]

What is a MAh?

 

[Jeff From NJ]

In July, my bill was $300 -
KWH Usage
1,949

However, I don't see any path to being able to run my 2 home AC units off solar, so I am assuming fans in a grid down situation.

 

[Supervstech]

100Ah is 1280Wh
100MAh would be 1.2millionWH...
How big are these batteries?

 

[Jeff From NJ]

The panels EACH are 260W, 30.6V, 8.5A

100 Ah with fat fingers

 

[Jeff From NJ]

100Ah is 1280Wh
100MAh would be 1.2millionWH...
How big are these batteries?

I connect directly to Three Mile Island ;-)

 

[Supervstech]

Ok.
Rereading, I see...
1280Wh max each battery.
So, 5120Wh total bank, recommended not below 80%, so usable daily at 4096Wh for 4 batteries.