Each solar panel in a solar power system needs a blocking diode in series with it to prevent the panel from discharging your batteries at night or during cloudy weather. I used a Schottky diode with a 3.3 Amp current rating. Schottky diodes have a much lower forward voltage drop than ordinary rectifier diodes, so less power is wasted. Every Watt counts when you are off-grid. I got a package of 25 31DQ03 Schottky diodes on Ebay
for only a few bucks. So I have enough left-overs for lots more solar panels
My original plan was to mount the diode inline with the positive wire outside the panel. After looking at the spec-sheet for the diode though, I decided to mount it inside since the forward voltage drop gets lower as the temperature rises. It will be warmer inside the panel and the diode will work more efficiently. More silicone caulk was used to anchor the diode and wires.