Also, make sure that if you add a diode, that the current rating of the diode is at least higher than the max current that panel is rated for. If you put in too weak of a diode, it will likely short, and then it is just like not having one at all. The other scenario is that it will open and you won't get anything at all. . .
Having fun yet?
This stuff gets addicting. . . when you start getting "free" power, you get hooked. . . fast!
Doug
Note: the term "free" power doesn't include the cost of making/buying/otherwise acquiring the equipment to make such power. . . That is like shipping when you order something. . . it is just a consequential expense to get on to the fun stuff!