We have a 50 watt panel on a stern pulpit modified to raise the panel 6 feet above thedeck and above the wind blade of the monitor self steering, For years I wanted to expand to 200 watts but I could not figure out a place to mount them.
Eventually, I realized that I only want the panels to avoid running the engine to charge batteries. When under way, we use the engine all day, or part of the day for propulsion. I need the panels only when we will be at anchor for more than a day. In other words, i can dismount and stow the panels away when we are motoring or sailing. I think we average 60-90 days per year underway, leaving 275-305 days per year at anchor.
I added two 80 watt panels. I wired them for easy disconnect. When we are under way, I stow them securely on top of the turtle and under the dinghy which we carry under the boom.
When at anchor, I found that I can very simply lash the panels on top of the mainsail which is flaked on the boom. When anchored in the keys where easterly winds prevail, I hang the panels from the starboard lifelines and use sticks to prop them at a 45 degree angle. That is optimal angle, and is never in shade. If heavy weather approaches, or we plan to weigh anchor, I stow them. The non-permanent mountings are simple and effective.
So, as others have already said, it depends on your use needs. The quantity of panels depends on your electric consumption. For us, the 12v refrigeration system is 80% of our load, and 210 watts of panels provides 100% of our needs almost every day. Even at higher latitudes where the effectiveness of panels is much reduced, it is enough, As I just mentioned, my needs also divide into periods with the boat under way and periods at anchor, so a non-permanent mounting of solar panels fits well.
You? You will have to think through your own use requirements.
