Fronius inverter high string voltage


So contacted the installer, and i also contacted Finn from solar qoutes, looks like “the system is working as intended and there is no issues here.”
The layout is indeed a East/West on one string and the rest on North.
They have referenced me this.

As well as a peer review paper on this sort of setup.
I feel like conditions needs to be perfect for this to work properly, and i doubt my 20+ degree roof meets the requirements.
Looks like I’m up Sh*t Creek here…I doubt i have the energy to chase this any further and just reside to the fact it is what it is.


i guess it is working as intended as they intended to cheap out and put them both on a single string.
i guess you could ask them what efficiency lost is or what they designed it to do?

it sounds like it works and not the end of the world. but your looking at a loss of probably 2-10%

now knowing how they are stringed i’m guessing:
MPPT1 is your East and West as your panels are rated just under 6 amps so the only way you can get more than 6 amps is to put them in parallel ie east/west. being only 6 panels your only going to get a max of 327v

MPPT2 is north and being 8 panels you will max out at just under 6 amps and have a higher voltage of 437v

so your volts and amps aren’t really comparable to each other

your DC volts don’t really mean too much as my West have nearly the same volts as my North (same amount of panels in string) early in the morning. while still shaded

Your MPPT1 seems to outperform MPPT2 basically all day so its working ok.
probably not the best but with that roof its probably a half decent install.

If you can compare your system against others with a similar system size you will know how good or bad it is.
if you are using the extra power in the morning and night then its probably worth the loss.

ideally all on the north would be best
i have 20 panels on the west and 10 on the north and the west is only doing 140% of the north. (in winter)


Yer so MPPT1 is 8 x North and MPPT2 is 6 x east and 6 x west.
So yer the inefficiency i would imagine is a little larger, its funny how 8 north facing panels can outperform 12 panels facing different directions…

My system seems to perform a little bit better then a dedicated East/West split (during the winter anyways) i suppose time will tell during the summer months if it’s performing ok compared to other systems that are similar.


hi just a thought for you. with fronius inverters if you go to the readout screen thats on the inverter it will give you a reading of how many KW s each MPPT has produced, so if you have less kws produced on the west east string of 12 panels than on the north string of 8 panels then there is your proof your setup is not working as it should. if you find this is so then you could get a electrican to disconect the 6 west panels in the switch on the roof on the end of the east array, and then take MPPT readings of the inverter to prove how well the system workes with the 6 east panels compared to the north array. so perhapps you will have on any day soon north 16kw, east- west 10 kw east only 13kw


no North is MPPT2

Good idea in theory and it would depend when the data is done from.

I have 20 on my West vs 10 on North and West is doing 150% of the North. (for the whole of August and 4 days either side)
150% of the North on 8 panels would be 12 panels
My system with only West no East/West on the same string comparable to rareox means both of his strings should work out about the same over August if the East/West on the same string isn’t causing an issue


This is the email i received from my installer.

MPPT1 is my North string.
MPPT2 is my east/west string.

Not sure where to get that display info jim, unless you mean it’s on the actual inverter lcd screen, or if it comes in a daily report format which i currently don’t download…


volts and current say otherwise… one way to work it out is turn off the north string and see which mppt goes down

yes off the inverter screen if you go to logs then scroll down to the total produced kwh there’s another enter type button that pops up that then shows another menu where u can go up and down and see the splits of mppt1 and 2


Thanks B-Man, yer i’ll turn off the North string on the weekend and see what mmpt goes out.
I’ll keep you updated on what i find out.