thanks so much for your support !
1. > What do you mean by “I’ll upgrade to 9S3P on each SPF”
It’s not about FW upgrade.
I just meant to add / upgrade a 2nd and 3rd string – 9 panels each – in parallel to existing 9 panels in series as I’ve already described above.
“Upgrade” from current 9 to 27 panels in total on each inverter.
Voltage is then 9x of a single panel
But max. current will be 3x ! (Short circuit current of course)
As far as I know the solar input of the SPF5000 consists of a boost circuit and it is designed for 18 (22) amps.
So in normal condition there should be never higher currents. Managed by the firmware.
But in case of the low side FET breakdown of the internal boost circuit of the SPF5000 there could be 3x Isc = 34 amps !
So I’d place one melting fuse ~25A on the solar input.
Of course each “9S” string will get it’s additional separate fuse mainly intended as breaker for service. ~16 amps each fuse. (The panel is allowed for 20A)