FoxESS Community - Owners & Installers Forum

My install is ongoing (long story), and so far we have 12 panels on an East-facing roof, and 6 panels on a West-facing roof. These are connected to a KH8 inverter. The panels have been split into 3 strings, 2 strings of 6 panels each on the East-facing roof, and 1 string of 6 panels on the West-facing roof.

The 3rd stage of the install (don’t ask why it’s run to 3 stages!) is the install of 6 additional panels on the West-facing roof.

Although I trust the installers, I’d also like to understand for myself what the best way will be to split these 24 panels across the 3 available strings? The East-facing roof shouldn’t ever suffer from any shading, whilst the West-facing roof is likely to have some shading towards the bottom gutter edge.

I’ve seen some references to string power generation limits of 3300 watts and 5500 watts. The user manual seems to suggest 8000 watts, if I’m reading it correctly (Max. MPPT input power (Per MPPT)). Depending on which is correct, this would dictate the max number of (450W) panels per string - 7 panels if 3300 watts, 12 panels if 5500 watts, or 17 panels if 8000 watts.

Consequently, is my rationale correct in thinking that it would probably be best to run all 12 panels on the East-facing roof on PV1, and then run the 12 panels on the West-facing roof as 2 strings PV2 and PV3 (2 rows of 6 panels each) to mitigate any shading from the lower row? This would only work though if the string limit is >5400 watts (i.e. 12 x 450)

The early versions of KH had a string limit set too low (thats the 3300 watts), the latest firmware supports up to 16A per string and that’s an effective power of 5500w at 360V nominal string voltage but obviously string voltage will depend on the number of panels and the panels used.

I would think that if you have 12 west facing 450W panels on a single string, you would expect it to clip at approx 5500 watts i.e. which is slightly higher than their rated output and something you might expect to see in perfect conditions in cooler weather - the panels derate slightly above 25C so it shouldn’t normally be a problem.

If the low row is going to cause shading the most effective way of treating that is to fit Tigo optimisers to the lower panels - they will allow the other panels to continue outputting even when the lower panels are in the shade.

Alternatively you can do what you suggest with the 2 east facing roof’s on a single string as long as they are the same direction and elevation and split the west facing roof over 2 strings, although you might still want to consider fitting Tigo optimisers on the shaded panels.

Or upgrade the KH8 to a KH9 (or bigger) which will give you 4 independent strings so you can have 6 on each - if your DNO is mandating 8kW output you can set a maximum export limit on the inverter to ensure a bigger inverter complies.

Thanks Dave - very helpful!

Upgrading the inverter isn’t an option, as it’s only been installed a few days ago.

I’ll discuss the other bits with the installers when they arrive this week.