Blocking Diodes, Fuses, and Charge Controllers

[phazaar]

Alright, so I have a fair amount of experience of commercial solar and 12V electronics, but very little of 12V solar - this has left me a few 'blind spots' that I'm struggling to usefully answer.

I've picked up a couple of 200W flexible panels for a system going on my van, and have a 40A MPPT controller on the way.

Looking at how to wire this up, I've spotted the instructions in the 200W panels state they're not suitable for use in parallel. This surprised me a bit, so I queried the manufacturer. Cue awful english->mandarin->english translation that has only really muddied the waters. They initially stated this was incorrect and they could not be used in series, then in parallel, then that either would be fine so long as 'the wiring is done carefully'...

My interpretation of this (I'd welcome others) is that they don't believe the modules could handle the increased current if one panel were to feed the other due to shading etc. Hence, would it be necessary/wise to use a blocking diode on the positive connection from each panel (I assume immediately before an MC4 T-connector)? If yes, should I also fuse each panel individually? Or would this be unnecessary to the diode? The T-connector could then go via a 40A fuse into the MPPT Controller, and this via another 40A fuse direct to the battery? I assume no fuses/diodes are necessary on the negative lines regardless - could these be used for an isolator switch though, or would this be better post-MPPT?

Many thanks for any help you can offer

[Mike90250]

Panels sometimes have internal Bypass Diodes to protect against localized shading on the panel. Either has it, or not, not something you can add. Sometimes they are in the J-Box for the panel and sometimes are replaceable.

Blocking Diodes prevent the battery from discharging into the panels at night. This function has been built into nearly every charge controller built since the 80's

I don't know any reason adding more diodes will improve anything, you loose about a volt going through them, and more than an amp, you need heatsinks

[bcroe]

The nature of panels of similar type at similar temp, is that the voltage curve is pretty constant with
varying shading, but the available current varies with light intensity. So like panels may be wired in
parallel and each panel or string will deliver its current capability. Somewhat shaded panels will
maintain voltage and continue current at reduced level, no blocking diode required. Bruce Roe