Solar PV 2 engineers gave conflicting diagnosis (SMA sunny boy)

Lablovezel

I have an 8-panel solar PV system installed in 2012 with an SMA Sunny Boy inverter. The system has apparently not generated since around 2018.

Engineer 1:

Inspected the system around the inverter/loft area.

Measured approximately 2.4V on the PV strings.

Said the inverter was probably not the fault.

Suspected a fault somewhere between the panels and the DC isolator, possibly requiring roof access and panel-by-panel testing.

Noted that the DC isolator was very stiff to operate.

Engineer 2:

Only inspected the inverter, AC isolator and small PV fuse box. He did not access the roof or panels.

Also measured around 2.5V somewhere near the inverter, but I do not know the exact test point.

Said there was a “short at the metal plate” in the AC isolator area.

Appears to have bypassed or rewired the AC isolator directly to the PV fuse box.

Told me to leave the system switched off for 30 minutes and then restart it.

Said that if it still did not work after the restart, the inverter would need replacing. The restart made no difference and the inverter still does not generate.

My question is: which diagnosis makes technical sense? If only around 2.4–2.5V is present on an 8-panel string, how could the inverter itself be the main fault? What tests should have been carried out to distinguish between a string/panel/cable fault and an inverter fault?

QrizB

The most common type of panels being fitted in the early 2010s were 60-cell panels with an open-circuit voltage of around 36 volts. An 8-panel string without any load, in sunlight, should be producing something like 250-300 volts.

If the string is only giving you 2.4V when disconnected from the inverter, it suggests to me that you've got a wiring fault somewhere (most probably on the roof) or possibly a failed panel. Not an inverter fault.

I have an 8-panel solar PV system installed in 2012 with an SMA Sunny Boy inverter. The system has apparently not generated since around 2018.

Have you owned this property for all this time, or have you only recently moved in?

paul991

If installed in 2012 are were you getting a Feed in tarrif payment?. Think the first Engineer is more near the mark .If you have to scaffold to further to fault find it may be best to upgrade the system with a higher capacity.

Lablovezel

https://forums.moneysavingexpert.com/discussion/comment/82094280#Comment_82094280

Thanks for your reply.

The engineer who inspected the system, later (after i told him it's still not working after the restart) he emailed me with the following update:

"The PV panels are generating 285V and there's 230V power coming in from the mains, so it looks like a new inverter."

Does that change your opinion, or would you still suspect a wiring or panel fault?

I just moved in 3 month ago.

Lablovezel

I have now successfully transferred the FIT account into my name, so I will continue receiving FIT payments until 2032. That means it's definitely worth repairing the system rather than replacing the other system (76p/kWH) installation.

I have 2 systems (west & east) 2x8 panels. The Samil side is working but unfortunately it has a sh*t tarriff (12p/kWh)

I'm not planning to upgrade the system. Personally, I don't think solar PV is a worthwhile investment anymore. However, as I already have the system and I'll continue receiving FIT payments until 2032, it makes sense to repair it and make the most of what I already have.

QrizB

"The PV panels are generating 285V and there's 230V power coming in from the mains, so it looks like a new inverter."

Does that change your opinion, or would you still suspect a wiring or panel fault?

That does change my opinion.

If the panels are giving 285V, and there's mains to the inverter, then it seems likely the inverter is the problem.

I seem to recall that the Sunny Boy has a fairly useful display that gives diagnostic information. Does that illuminate? What does it show? Can you share a photo of the screen?

Lablovezel

https://forums.moneysavingexpert.com/discussion/comment/82094433#Comment_82094433

photo_10_2026-05-31_01-04-11.jpg

photo_12_2026-05-31_01-04-11.jpg

photo_13_2026-05-31_01-04-11.jpg

photo_14_2026-05-31_01-04-11.jpg

photo_15_2026-05-31_01-04-11.jpg

photo_16_2026-05-31_01-04-11.jpg

photo_25_2026-05-31_01-04-11.jpg

Yes. If I tap on the display, the backlight comes on, but no information is shown at all. The screen remains completely blank.

paul991

would it be easy for you to swap inverters round

Lablovezel

https://forums.moneysavingexpert.com/discussion/comment/82094488#Comment_82094488

That's a good idea. However, several experts have told me that even if the Sunny Boy turns out to be working, I should still replace it because it's now around 14 years old and likely nearing the end of its service life. So I think replacing it is probably the best long-term option anyway.

paul991

I started out with a samil inverter in 2014 they told me it would not last over 5 years ,was still as good as new when I removed it last month to fit battery.

sheenas

The inverter is going to switch off below around 16volts. I suspect therefore engineer 1 was correct.