is about 12"x24" and costs less than $100 these days. That size panel can be wired directly to your batteries without a controller. Alternatively you can use a cheap controller.

On Seaquestor I mounted two 20 watt panels on the cabin top just forward of the spray hood. They are wired via a cheapo controller to my house bank (no need to leave the battery switches on). Those two panels put out up to about 2.5 amps at noon in direct sun and average about 15 amp-hours per day on sunny days and 4-5 amp-hr per day on cloudy days. Since we don't have refridgeration, the solar panels provide enough current to run the electronics (chartplotter and depth instrument) while underway. Charging when we are on the hook replaces what we used with the electric winches unless we were doing a lot of tacking in heavy air.

On Tortuga I have two 50 watt panels on the cabin top. They out out a maximum of 7.2 amps and average about 40-50 amp hours per day on sunny days and 10-12 amp-hours on cloudy days. Those two panels will keep up with my bilge pumps and let me leave my refridgeration on full time. The only down side of the installation is that during an engine run the panels can pull the batterises up to nearly 14.5 volts. Thay voltage level drives the smart regulator on my alternator nuts and creates an error state that sets off an very annoying buzzer. I installed a disconnect switch for the panels to circumvent that. We also have a cover to put over the panels to shut them down.

Finally, last year I used white tarps to cover both boats. The solar panels get enough light thgrough the tarps that the batteries stayed fully charged all winter