Hi,
I have a 24v system for my engine starting only using 2x110 ah 12v batteries in series.
I have installed 2 x 10watt solar panels connected in series running thru a Stecca 12-24v controller. This should produce enough current to keep the battery topped up over winter with a margin extra and the stecca will not let it over charge.
I have another 40watt panel charging my domestic batteries via another stecca controller , 2 x 230amp hr deep cycle. We have used better end panels brought over to France from New Zealand.
When I am on the boat I connect all 3 panels in parallel (60 watts) to boost domestic batteries which should provide enough to power my Engel fridge if I moor for a few days.