Solar panel

[noelex]

I agree that this is the best set up except I would have the two panels at an angle, preferably 45 degrees. Mount them like the navigation buoys and highway solar panels. Having them flat means that when the sun is hitting them at a reasonable angle they are also expected to work at the hottest time of the day and performance drops off above 25 degrees c. Black panel will get to 25 degrees fairly fast.

Solar panels will produce the maximum output when they are orientated at right angles to the sun. They will heat up but the grater radiant energy captured will more than make up for this.
Fixed ground based panels are angled only so they are on average in the position where they will collect the most sunlight, based on the position of the sun which can be determined from the latitude of the location.
Navigational buoys often have panels angled for a different reason to discourage birds and there droppings.

On a boat if you can angle the panels point them so they are at right angles to sun and capturing the most energy.

 

[VicMallows]

I bought a pair of 40w 'domestic' panels and simply played with them on the boat. I soon learned more about position/shading/charging characteristics than I had studying all sorts of technical reports.

I have established my optimum 'compromise' position which works well, but if in desperate need of a boost to the batteries I will go to the trouble of positioning them optimally which just about doubles the output.

Vic