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Posts: 1
Reply with quote  #1 

Can someone help check my calculations for number of solar panels and batteries?

I currently have:

1x 285 watt panel

1x charge controller

3x  batteries wired in parallel (total of 291 Ah capacity or: 291W *12V= 3492Wh


Power Requirements:

I’m running IR lights and security cameras off of 12V so no need for an inverter. I estimate that I’ll be pulling about 16A constantly or at 12V (16A*12V =192 watts or 192 watts * 24 hours = 4608 watt hours required).

This means my demand is more then my capacity, so should I should increase to 4 batteries in parallel giving me a capacity of: (4 X 97Ah each battery) *12V= 4656 Watt hours.


Solar Panel Power Output:

 (one 285 watt panel) * (5 hours of sun) * (.66) = 940 watt hours produced.


Since I need 4656 Watt hours from my calculation above, that means:

4656 watt hours capacity needed/940 watt hours produced from one panel = 4.9 panels (round up to 5 panels)


So it looks like I need 5 panels and 4 batteries in parallel. Do those calculations make sense?


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Posts: 3,040
Reply with quote  #2 
Your calculations look ok but I have some questions.
First your lights. Can they be replaced with LED lights to reduce power draw?

"5 hours of sun". Where does this come from? Without knowing your location there is no way for me to calculate the actual energy harvest to expect.

Do you expect to run this load 24/7? If so what provision do you have for bad weather? You need batteries to carry the load through the storm, AND you'll need the PV to recharge them.

Also bear in mind that it's generally not recommended to discharge your batteries more than 50%. This cuts their usable capacity in half.

Is PV your main source of power or a backup?

Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
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