Fronius inverter high string voltage


I have a question, My system has 2 MPPT Strings, an eastern array and a west/north array (bad roof layout)
So i noticed that my eastern array voltage is far higher than my N/W array but produced less amps.

Is this due to the inverter trying to get the most out of the array and with the lower resistence it causes the voltage to be a lot higher ? Or is there something more sinister at play here.

My eastern array has 6 panels i believe but i’m not overally sure, added a picture of what this looks like MPP2 is the eastern array.

I have 20x Sunpower E20 327w Panels and fronius 5kw inverter.


well from the screen shot it looks like you have 6 east and 2 north panels on no mpp 1

and the rest ,the other 12 panels on the north an west roofs on no mppt 2,

worked out like this,

mppr 1 8 panels 2565 w 317.54 v X 8.26 a= 2622 w ==39.69 v per panel.

mppt2 12 panels 2145 w 429.47 v X 5.1 a = 2189 w == 35.79 v per panel.

not how i would have wired them because the weaker output panels in a string will always pull the top performing panels down to there leave, so i would have used jimko maximum panels or micro inverters, or changed the panel layout on the roof to suit a 2 mppt inverter,


Not sure if you checked my profile of my roof i have pictures on my profile, but yer i agree that the layout should have been different.
The company i went with seems to think there is nothing wrong with how the system is performing as expected and i doubt i could get them to fix the layout.

I will check tomorrow but i thought the Mppt 2 was actually the east side string though, regardless i think you are correct in the panel layout pulling the specific string down.

Cheers for the response Jimdcollie, i do appreciate it a lot.


well there may be a way if you like to try.
if you would like to PM me your address i can use the satellite to look at your roof and a photo of how the panels have been installed, then i can work out how it should have been done.
is your inverter a fronius 5.0.1 Australian or an international module ??
i would also need your pvdo id for your system and also your Fronius solar web log on so that i can see a live screen of your inverter to work out exactly how much production you are missing out on, guesstimate from what i can see at this time is about 30 % of total output missing.
i can use your location and a solar modeling tool to show what you should be getting.
then you have hard facts to take to your installer, if they then are not interested in fixing there mess then there other people you can take your case too,bad publicity on the Internet and solar web sites can very soon kill a bad solar installers business, if you are in Australia i am thinking you paid way more than $6500 for your system installed which is about what a good 6.6 kw with a 5 kw inverter costs without the most expense panels a lot of money can by ie sun-power.
mppt 1 made 97% mppt made 55 % a big loss in output, as there is no inverter amps showing i can not tell how good the overall efficiency is. i am thinking your east set of panels is not due east as the output shown at 11.55 is to high for that Jim


Hey Jim,
Yer I’m in Perth Western Australia, you are correct, i paid a premium for the panels, the Inverter is the international version.
If i had my time again i wouldn’t have gone with the company i did, and made some different choices for sure.
It’s a nice offer you have given me, though i don’t feel overlly comfortable about giving out my login details to the fronius web login.
Though lucky for me I believe the guest login function would allow you to see the data you need?

I really appreciate your time in responding to me.


its better you are comfortable with what you do so a guest log in workers for me, i would still need your address thought so i can see your roof you can PM me through pvputput i am jims maxim jinkos, then i will share my po no and we can talk about what i may be able to do to help you Jim


got your message thanks ,food for thought for you,If you have 12 panels in series then thats 778.8 volts at no load and 656.4 v at mvoc.
Australian rules state a max of 600VDC for a house pv system, so you may have a complaint you can make stick against your installer to get them to move you panels and rewire then properly .
i would have for 2 sets of 10— 13 on the east roof and 7 on the north roof, NONE on the west roof,
superpower e20 327w panels show nov of 54.7v and max soc of 64.9 v they are classes as high voltage panels because of this and therefore cannot be used in strings of more than 9 and stay within the ADR,s although the other 12 may be wires id 2 strings of 6 and then paralleled in to the inverter, voltage is near for this,
i have no scale on the photo you sent,so cannot size properly— it looks like if on the north roof of 3 staggered panels if panels were fitted down line of roof then 7 panels would fit on this north roof section and with the 3 all ready on the other north roof makes 10 wired i 5X2 on one mppt in the inverter,move the others to the east roof and wire in5X2 again on the 2nd mppt in the inverter and you have a system that will comfortably make 10,000 kw a year, other things to note its better to have 6mm sq DC wireing on split arrays much less volts drop,and yes the panels can be installed like i say just takes the installer some more work so you end up with 2 arrays not 3 as there are only 2 mppt to use in the inverter,if youe installers name starts with s and is in Malaga then there local bloke came here to quoit me for 70 kw of systems, he said they would not install what i had asked for and if i did not wont what they wanted to sell me then i might as well show him the door << well i showed him the door > you might want to mention to them you are going tp post a review of your job and lack of service on and if you get it fixed you can list it as having a 2nd array on pv org which will give more accurate isolation fingers to use jim


FWIW, I have 12 on one string as well, @ 34V per panel thats only a shade over 400V.


I recall the installer saying they would run the some of the panels in parallel.
There is enough room to set the panels up the way you suggest, i don’t understand why the installer wouldn’t have suggested this in the first place if that would have made me more power through out the day.
The company i went through is one of the bigger installers who “prides themselves on their quality of work”

My roof is pretty vile though, this is the suggested layout, it ended up slightly different but the panel numbers are the same directions regardless.



All panels in a string should be facing the same way +/- a few degrees. If they are not the panel with the least sun will determine the max current. You have 3 different angles, you need 3 different strings unless you put the East string in parallel with the West string in which case the string with the least sun will not contribute as much as if it was on its own string. Not sure how your inverter handels the voltage difference between the 8 panel string and the 2 6 panel strings.I think you would get a significant output increase with a 3 MPPT pint inverter or a micro inverter system. The MPPT point will be different between the East and West string as the sun goes overhead. The extra output may not be enough to justify the extra inverter cost.


Hey John,
Yer these are my thoughts exactly, the system is just over 3 months old, how could i justify changing my inverter after spending a good amount on this system already.
I think my only option here would be to change the orientation of the panels to 2 directions an east and north split.
But again i would expect this to be at my own cost, and would i gain a sufficient amount per day over the current layout or would it only be minimal and wouldn’t justify the cost.


The other thing might be to consider installing optimisers on the panels - that might or might not be cheaper than changing the inverter.
I’ve got 3 orientations on my roof - MPPT1 is 1 string of 12 panels facing west, but MPPT2 is a single string, of 4 x north and 6 x east facing panels. I put Tigo optimisers in, so the north+east panels would work properly.
They can be installed by lifting the panels in-situ and mounting them on the back of the panels, so its not major surgery to install them after the main installation.


HI When parallelling into 1 MPPT, every panel needs to have a Tigo optimiser, otherwise, you will have significant voltage differences between the paralleled strings. Selective deployment only works when you have one string into an MPPT. so when 3 strings into 2 mppts and i string is on 2 different directions and the other string is also in 2 directions and runs a parrallel set up you need to have them on all panels installed to get useful output and minimize pid on the higher voltage panels as well.


Changing the roof layout looks like a lot of work. What about adding one more inverter so you can get three strings. Your present inverter may not be able to handle the peak load if all the panels are on at the same time. You could try disabling one of the parallel strings and see how much you lose. Then try the other string. If the sum of the two separate strings is not significantly larger than both stings together, the ROI will not justify changing anything.

To go much farther than that you need to know the input specification on the inverter and the actual currents and voltages of each string. I am guessing the East, and West panels are in parallel strings, and the North panels are on the other string.
A low pitched roof will make the East and West panels look like they are tuned together while a steeply pitched roof will make them look like they are two different times of day for peeking output. Both will work well together, but there is a point about 4/12 where they will not produce as much as if they are on different MPPTs. All that is just me thinking could be that what you have is best for you.


Just for everyone playing at home, this is what the setup is in my paperwork.

So my understanding of this is as follows.
Mppt1 = 6xEast & 2xNorth
Mppt2 = 6xWest & 6xNorth

I want to contact my installer and ask them if this is really the best setup, when i could have had a North and east split instead and it seems to me that would see better output and would have been easier to install originally ?


I would have interpreted that ‘System Config’ table differently as:
MPPT1 = 8 x North
MPPT2 = 6 x East & 6 x West


You are probably right Will, just going on what the sales man pitched me as well, though it does make more sense, also there are 2 x isolators as Jim pointed out to me, one on the East and one on the North.


if you have 3 strings you should have 3 isolators.

I have a fronius and my west is in 2 strings running off MPPT1 and 1 string on the north on MPPT2 as the MPPT2 can only handle a certain amount of amps and havings 2 strings doubles the amount of amps. where as the MPPT1 can handle alot more amps

you would think its 1x8 for north and 1x6 east, 1x6 west but you never know. i honestly don’t know why they didn’t just do 6 east 6 north and 8 west. those 2 on the north way off by themselves would of been a heap of stuffing around to just get them if especially if they did run them in the same string as the north.

whos to say the 2 north aren’t connected to the 6 east.

if you want to find out then you need to get in the ceiling and see where they have run the conduit. or get on the roof and see if you can see where the 2 north panel wirings goes


I have contacted my installer to chase down how it’s wired up, so we will see what they say, my last email basically said the system was performing as expected so not sure if they will come to the party tbh.


@rareox any news?