I have 200 watts of solar on the RV roof. In Ohio, the sun currently is at an extreme angle from the south - not even close to being directly overhead. Even so, I'm getting almost 5 amps into the batteries. With fairly heavy overcast I still get around a constant 2 amps... PLENTY to keep the batteries "healthy".
I did not install solar as a replacement for traditional battery charging (Shore power, generator, coach's alternator). It is merely a supplemental charging source when NO DRAIN (other than normal self-discharge) is placed on the batteries.
Mainly it's a storage solution - providing PLENTY of amperage to keep the batteries fully charged/cycled when the RV is sitting idle, or in winter storage. The alternative was to run an extension cord to the RV and use a battery maintainer.
If you're only getting .3 amps from a 100 watt panel (in direct sun), I would suspect there is an issue with your solar installation. I would check cabling, etc., because the numbers don't add up.
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