Your Siemens M55 should be a mono-crystaline panel, rated for 53 watts and 3.35 amps the SM-55 panels were rated for 55 watts and 3.45 Amps. When you start paralleling larger numbers of panels, you should think about fusing the panels individually in case a wiring problem should develop. If you add fuses, 5 amps for the M55 panel, and 2 or 2.5 for the thin film panels should be about the right ratings. Ideally they will never blow unless there is a problem.
You most likely don't need them, but I have also added diodes to each string on mine as I feel that the extra protection is worth the voltage drop especially since my panels connect directly to my 48V battery bank. The penalty of about a half a volt lost in the diode is substantial for a 12 volt system however at about 3.5 to 5% of power produced if connected directly to a battery (.5/13.5*100) fortunately, this won't really show up as a loss when connected directly to the battery except when the voltage is too low. This is because the amps increase relatively little from peak power to short circuit current. The power would have been lost anyway when the panels output voltage was forced to that of the battery. The losses show up when the panel voltage is between the battery voltage and a half volt or so above it as the panels won't have the voltage to charge at all through the diode. For your Siemens panel, it will pass through those voltage ranges relatively quickly at dusk and dawn. If you had the Siemens 33 cell panels that would be more of a problem than with your 36 cell M55 panel especially in hot weather when the panel voltages are lower. If using an MPPT type of controller operating at 16V then the losses would be about 3% most of the time. (.5/16*100). Again, though, I wouldn't add diodes in series for your small array of panels unless there was some other need for one such as if you were connecting them directly to the battery instead of through a charge controller, which most probably already would have a diode to prevent battery power from leaking into the panels at night. If I were to add diodes, I would add one to each panel before they are tied together as this not only prevents battery power from flowing into the panels, but prevents one panel from feeding power into another in the event of an unusual failure. It also would allow the use of a diode rated for the peak panel current instead of one rated for the total amperage of the array. Rich
