First Solar Experiment, a few calculations questions.

jleblan1jleblan1 Registered Users Posts: 5
Longtime reader, first time poster.

As an all things electronics tinkerer Im doing my first ever solar project. Im looking to setup 3 lights (1 under caport, 2 on fence in dark corner of backyard)

Heres what I have so far.

QTY 2 10 watt Solarland mono crystal panels purchased last year on clearance at a local agriculture outlet.
QTY 3 1.8 watt 12V LED edison base purchased at a local RV shop.
QTY 1 8.5AH 12v AGM Battery
QTY 1 Solar Charge Controller with Digital Light Timer.
QTY 1 12x12x6 Sealed junction box.
QTY 1 50 Foot Spool 12AWG Wire
Mounting hardware.

Heres my calculations.

20w X .77 efficiency = 15.4w

15.4 x 5hours of South Louisiana sun = 77watts

77 watts x .77 efficency of charger = 59.29w


So 4.78 amps generated on a sunny day

(Charge Controler).72w/12v=.06a

Total Load .51a

Timer set to run 5 hours per night

5hour x .51a = 2.55a per night

8.5ah Batt / .5 Depth of Discharge Headroom= 4.25ah

Now my questions.....

1. Are my calculations sorta right?
2. Do I have enough headroom to not trash my battery on a few cloudy days. I can drop down to 4 hours of lighting a night.
3. Is it OK to use a mostly sealed junction box, will the small holes for my wiring be enough for venting of gases from the battery?
4. Any other considerations of advice?


Why do i feel this may turn into an addiction?


  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: First Solar Experiment, a few calculations questions.

    seems to be right. do be sure of the battery charge specs and be sure the controller can meet those specs. i say this because you don't want this to go beyond it specified charge voltage or it will gas and agms aren't supposed to gas or it will degrade them. by that you don't need to vent, but you could put a small hole at the bottom of the box to drain out condensation that may accumulate inside. keep in mind water does not need a big hole to drain and the bigger the hole the bigger the insects that will make that their home.
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