I don't have diodes on the individual panels. I've read where people recommend they be used, but I've also read reliable sources that say they are not necessary. I just don't know how much, if any, a lighted panel will back feed into a shaded panel. And yes, I do have that situation at my site with trees casting shadows in the morning.
I would have agreed, once upon a time.
I have a moderate PV install. 6 arrays each of 600 watts. 4 of them on trackers.
A horrible little tale for you. When I installed the last array, it was about mid-day that I was ready to go. Just like the other arrays, as I got them done, I plugged each array in in parallel with the others. Each other time this was usually late afternoon. This time it was peak production. Well, I plugged in the cable and..... there was crackling and snapping and popping all around me.
Every panel (6) on this last array had to come off. Inside their J-boxes looked like this:
And a handfull of little rattly bits fell out, like these. Do you recognise them?
At the time, I was gutted. I was lucky, the company I purchased the panels from (in china) couldn't help me enough. Concerned and wanted to send me replacement panels, was delighted that I thought it was just the diodes and sent me replacements by overnight international courier.
All the panels came back working once I'd replaced the diodes (thankfully). It is my belief that it was the instant connection of around 120V DC to the array that caused a cascade/avalanche in the schottky diodes, allowing them to pass very substantial current. (The rest of the arrays were producing around 2.8kW at the time).
Since then, I added (as I should have in the first place) - series schottky diodes for each array.
I bolted each of them to a copper busbar for both electrical interconnect, and thermal dissipation.
The thin wire on the leads is very short. It is thin so it doesn't have a tendancy to break the leads off the diodes, and it will make a fusible link in the event of some catastrophic failure.
I now get zero current flowing back into any array, regardless of which ones are in shaddow (clouds moving past, arrays shading each other, etc), and I will never get another incident like this and blow up a panel.