"Here - Hold my Beer"
- Nov 13, 2019
PV panel 40W
battery 100 Ah
Battery - is that FLA "flooded lead-acid" wet cell? Or sealed, like AGM or Gel?
If FLA, it wants 12A, so 150W or more of panels for a 12V battery
If sealed, I'm not sure how slow a trickle charge is OK, but can probably take 10A, maybe 20A.
Expect 5 to 6 effective hours of sun in the summer, 1 or 2 in the winter (check an "insolation" website for your location.)
6 x 40W = 240 Wh, 1 x 40W = 40 Wh
Compare that to battery, 12 x 100 = 1200 Wh.
The inverter probably wastes 25W just sitting there, so if turned on for one hour, there goes 25Wh. Left on 24 hours per day, 600Wh drained.
Check out Craigslist for local used or extra PV panels.
You might pay between $0.10 and $0.50/watt.
Catch is, most big cheap panels are 24V or 36V
You have a PWM charge controller, which needs a 12V panel (Vmp in the 17V to 20V range.)
To use the higher voltage panels you would need an MPPT charge controller
At this point I would recommend she scrapes the PWM and get a cheap MPPT 12/24 volt SCC that can take a larger panel (higher voltages input) -- and then like you said - search craigslist for a single good size panel that can push probably 250-350 watts... that will keep the battery charged to full almost all the time which AGM's like plus allow her to add more and more lights in the future ...