On my sailing boat we've installed four solar panels (two times Vmp = 17.64V, Voc = 21.6V, Imp = 5.67A, Ioc = 6.07A, Pmax = 100W and two times the same but 75W), which we connect all in parallel, then to an MPPT system from Mastervolt which serves the 12V batteries and autopilot.
The solar panels are not exactly equal in voltage (Voc 21.6V and 21.2V) but in parallel that averages out. They're 2nd hand and were in working condition.
When we connected them in parallel, we accidentally had the system through the MPPT Mastervolt connected and all four minuses (3 panels, 1 Mastervolt) got connected with one solar panel's plus. Accidentally (we did inspect the voltage and pluses prior, but still screwed up). Then we connected the rest, all pluses (so we thought), saw a spark, disconnected, reviewed, and found that one panel didn't give voltage anymore. The bypass diodes (it had two) were burnt and split in two.
I read somewhere that short circuiting solar panels should not break them as the Imax can never get higher, but apparently we broke it anyway. This lead to some questions:
- clearly these were wrongly connected, what happened here and why did it fry the bypass diodes? There was no shadow, current should not flow through the bypass diodes, right?
- without bypass diodes, good panels should still give power, correct? [After frying, that panel gave zero on V meter. Is it possible one (of three) bypassable cells was already broken and the bypass was always in use?] Edit: this was wrong, they still have 20+ V.
- these exact type schottky diodes are not available anymore, is it safe to select any diode with the same or higher specs (these were 80SQ045, rated 8A, 45V), as long as it is 'schottky' type? If I install two diodes in parallel (there's room), does that improve performance?
- could it be burned solely because it's 10y old? The other panels seem still fine.
I tried to find answers to the above online and did find how these things are supposed to work, and that they break, but no info on how or why it breaks, let alone what happens when you screw up like we did. Hopefully someone here can help solve the mysteries or if not, help with the main question, selecting proper new bypass diodes.