We use solar panels on Morning Star. I mount one on each side of the stern pulpit. I have found that one 3 amp panel per group 27 battery works well (we don't have refrigeration). At first we used two group 27 Gel batteries (battery one and two) and one solar panel connected to one of the batteries. This worked, but we had a time when we could not run the engine and it was cloudy. After 6 days our batteries were kind of low. So I added a group 24 Gel as a starter battery and connected the two group 27's together as a house bank and used two 3 amp solar panels connected to the house bank. The 2 panels keep a charge on the batteries and the only time the batteries get low is when we use the water maker a lot.
In the picture to the right, you can see the mount that I use to connect the solar panels to the stern pulpit. It started out as a temporary bracket to see how I wanted to make it. I have changed it three times and now like the way it works. It is important for the mounting bracket to be able to move to get the best angle to the sun. In the morning I have the panels angled down so whichever way the boat swings one side will get sun. In midday I have both horizontal to get sun and then in the evening they go back down so that one will get sun. You want your mounts to be set so that if you are not on the boat they will still get sun. You do not want to have to stay on the boat to move the panels just so you can have electricity.
The mounting bracket is made out of 3/8 inch plywood and 4 of those white rail mounting brackets that you can get at marine hardware stores. I have been using the first solar panel since 1992 and added the second one in 1995. The current brackets have been in use since 1995. The last change was to add a lift between the rail mounting brackets and the plywood that connects to the solar panel. That lets the panel tilt above horizontal to catch light from the other side. This is because the solar panel extends past were the stern pulpit curves. The curve will block the panel when you get to horizontal. Now that I know how they should look, I will someday make them out of rectangular aluminum tubing to make them lighter. These have worked in 50 knot winds so they are OK. I did put them down to the position that you see in the picture so there would be no lift.