We have two solar panels on DRIVER. Both of them are Siemens. One is 75 watts, the other is 46 watts.

The trick with solar panels is to put them in a place where shadows can not fall across them. On a boat this is impossible--unless they are mounted on the top of the mast. (I have actually seen this done...!) The worst place to mount them is on top of the dodger. The mainsail will create shadows, and if you rig a sun tarp the panels will be in the shade.

Shadowing is a big deal. Even a pencil-thin shadow created by a backstay--which might only cross a few cells--will effectively reduce amperage output by 20 percent or more. Being able to adjust the panels so that the surfaces remain perpendicular to the sun will create a huge boost to output--by as much as 50 percent.

Placement:

Except for the top of the mast, the next best place to mount panels is aft, over the cockpit. When I bought DRIVER's panels I had aspirations to fabricate a sophisticated arch-system to support them, complete with adjustable mounts. Unfortunately, I ran out of time, and money, and put them up "temporarily". That was 6 years ago! Ours are bolted to 1/4 inch thick, inch-and-a-half, by inch-and-a-half, aluminum angle bar. These bars are fixed to the backstay using U-bolts. It is a less-then-perfect mounting solution because they wobble at sea. They are also a pain when I have to take the backstay down at boat yards to haul out. My suggestion is to engineer a reliable, and strong, arch system onto which the panels can be mounted. How you do this will depend on the design of your cockpit.