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Old 02-18-19, 06:31 PM   #26
BillG
Lurking Renovator
 
Join Date: Jul 2016
Location: Minneapolis
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Well, I said it before, but will say it again. The number came from PVWatts. This is the gold standard tool, from the National Renewable Energy Lab, NREL. Since you used Sacramento, so did I. I don't think it is good policy to give a wild guess when someone asks for advice.

100 watts is fine for panel size if using an MPPT charge controller. Using a cheapo is fine, too, but he'll need at least a 130 watt panel for the same charging capacity. If he wants to charge his battery faster, simply pick a larger panel.

The charge controller should also control the lights - on at dusk, off at dawn or some user defined number of run hours. It should have a proper low depth of discharge protection.

Why mess with conjuring some electronic circuit and hacking a light bulb apart, when you can just use a 12 volt bulb?
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