On Thursday, 28 March 2019 21:43:02 UTC, wrote:

You're surely joking. What's needed is a small solar panel, nothing like 100w, and a diode. The diode prevents the panel flattening the cells at night. If the panel is sized large enough to exceed a wise charge current, add a shunt voltage regulator.


Take care what type of diode - you need one that does not drop too much voltage in the forward dircetion. In general the leakage (in darkness) of a PV panel is very small. I lived on a boat for 10 years using solar panels for electric power and never needed a diode. I just had the PV panel connected directly (with a fuse) to the lead-acid accumulators.

I do agree that you need some kind of regulator (in my case it was me disconnecting the battery when fully charged). it is a bit easy to fully charge and then 'boil' (i.e. electrolyse) off the water if the battery is left on charge for long periods withjout being used.

I used several 100 W panels wired in parallel.

Robert