SMA Sunny boy dual MPPT inverter question

[eah123]

I'm getting conflicting answers on this from 2 different installers.

I'm in the process of designing my rooftop PV system.

The PV design will require the use of 3 roofs - 2 south facing and 1 east facing.
Plan is to do
South facing roof 1 - 11 panels
South facing roof 2 - 9 panels
East facing roof 6-8 panels depending on panel wattage

One installer says that a single SMA Sunny boy with dual MPPT inverter (SB7700TL-US-22) can handle all of the panels.
The other installer says even with dual MPPT, you will need a second inverter.

Who is right, and why?

Thanks

[sensij]

If you had strings of equal length, a single inverter would be OK. With all three faces having unequal strings, a 2nd inverter would be required to maximize output.

[eah123]

If you had strings of equal length, a single inverter would be OK. With all three faces having unequal strings, a 2nd inverter would be required to maximize output.

What is proposed by the installer who wants to use just one inverter is
string 1 - 20 panels (south roofs)
string 2 - 6 panels (east roof)

Bad idea?

[inetdog]

What is proposed by the installer who wants to use just one inverter is
string 1 - 20 panels (south roofs)
string 2 - 6 panels (east roof)

Bad idea?

Unless you have a serious partial shading problem, that combination should work just fine.
Some inverters have a maximum power per input which would require a more balanced allocation of the panel power between the two inputs, but I do not think that will be a problem with that SB unit.

[sensij]

What is proposed by the installer who wants to use just one inverter is
string 1 - 20 panels (south roofs)
string 2 - 6 panels (east roof)

Bad idea?

20 panels is too much for a single string, they must be doing two strings of 10 in parallel. That means one panel from the 11 panel roof is in series with the 9 panel roof. Are the two south roofs both at the same tilt? If not, you might still see some loss with this design.

[truav8r]

SB TL inverters have 2 MPPT inputs, and you can have 2 strings on each input. With that info, I'll let the experts here speak to optimum panel setup for each MPPT input.

[eah123]

20 panels is too much for a single string, they must be doing two strings of 10 in parallel. That means one panel from the 11 panel roof is in series with the 9 panel roof. Are the two south roofs both at the same tilt? If not, you might still see some loss with this design.

Yes, the 2 south roofs have the same tilt.

[solarix]

Even though there are 2 inputs, they can't be too imbalanced with too much power on one. SMA used to spec it at no more than 66% of rated power on each input, now they spec it at max input current of 18A (for the 7700). 20 panels (2 parallel strings of 10) would be right at the limit of what one input could handle - but should do it.

Using multiple orientations is very cost effective as you can seriously oversize the array because they never reach peak power at the same time of day.