I have a 8Kw Sunsynk inverter with 2 strings and 545w panels (5 per string) Info attached)
What is the max number of panels I can put on each string?

@AndreGreyling

At STC (25 Deg C), your Voc will be as follows:

Depending on where you are, you need to compensate for the Temp Co-efficient, which for your panel is -0.25%/Deg C. Assuming 0 Deg C minimum temp.

which will take an 8 series string open circuit voltage to 425V, that is on par with the MPPT's maximum useable voltage.

27 minutes ago, Sidewinder said:

@AndreGreyling

At STC (25 Deg C), your Voc will be as follows:

Depending on where you are, you need to compensate for the Temp Co-efficient, which for your panel is -0.25%/Deg C. Assuming 0 Deg C minimum temp.

which will take an 8 series string open circuit voltage to 425V, that is on par with the MPPT's maximum useable voltage.

Thanks for the info, I am in Cape Town
So the max will be 8 panels?
Can I have 8 on one string and 5 on the other?

Edited June 13, 20251 yr by AndreGreyling
info needed

56 minutes ago, AndreGreyling said:

So the max will be 8 panels?
Can I have 8 on one string and 5 on the other?

yip you can do 8 on the one mppt and 5 on the other mppt or try fit another one so you can have 7 on one string and 7 on the other that will give better voltage matching but not critical :)

5 minutes ago, WannabeSolarSparky said:

yip you can do 8 on the one mppt and 5 on the other mppt or try fit another one so you can have 7 on one string and 7 on the other that will give better voltage matching but not critical :)

Thanks!

I have 6 on one string and 4 on another

The 6 are 3 x 2, facing east, north and west. Highest voltage I have seen is 228 volts

The 4 are 2 x 2 and can reach 185 volts. Both face west

On 2025/06/13 at 12:02 PM, WannabeSolarSparky said:

yip you can do 8 on the one mppt and 5 on the other mppt or try fit another one so you can have 7 on one string and 7 on the other that will give better voltage matching but not critical :)

Forgot to ask - don't you also have to take the panel's current (Impp/A) into account when determining the number of panels?

(I am a novice with solar!🫣)

7 minutes ago, AndreGreyling said:

Forgot to ask - don't you also have to take the panel's current (Impp/A) into account when determining the number of panels?

(I am a novice with solar!🫣)

Not necessary when fitting panels in series, in series the volts keep adding up the more panels you add, the amp output will stay the same.

There are some inverters that have a max amp input as well, but unless you are fitting the big > 550w panels it shouldn't be an issue, but it wouldn't hurt to arm and cross check with your inverter specs.

6 minutes ago, MrBeauvedere said:

Not necessary when fitting panels in series, in series the volts keep adding up the more panels you add, the amp output will stay the same.

There are some inverters that have a max amp input as well, but unless you are fitting the big > 550w panels it shouldn't be an issue, but it wouldn't hurt to arm and cross check with your inverter specs.

Thanks, it make sense!! It is 26A but is that per MPPT or total for both (my Inverter has 2 MPPT'"s)

1 hour ago, AndreGreyling said:

Thanks, it make sense!! It is 26A but is that per MPPT or total for both (my Inverter has 2 MPPT'"s)

It's 26A per MPPT. Right now it sounds like you are using 1 string of 5 panels per MPPT, and each of those strings will max out at 13A.

What you could also consider, is to put your 2 strings in parallel (NOT SERIES!!!) onto one of the MPPT's, so that one can reach up to 26A. This works say if all the panels are facing one direction.

That would leave you free to put anything else on the second MPPT, say if you had roof sections facing East & West, rather than all North. Bottom line, you have options.

38 minutes ago, GreenFields said:

It's 26A per MPPT. Right now it sounds like you are using 1 string of 5 panels per MPPT, and each of those strings will max out at 13A.

What you could also consider, is to put your 2 strings in parallel (NOT SERIES!!!) onto one of the MPPT's, so that one can reach up to 26A. This works say if all the panels are facing one direction.

That would leave you free to put anything else on the second MPPT, say if you had roof sections facing East & West, rather than all North. Bottom line, you have options.

I have 2 strings with 5 panels each and want to increase one to 8 (545w) panels.
Where can I see if I am using one string per MPPT and not perhaps just one MPPT with 2 strings on it?

The way these Inverter manufacturers specify some of the parameters is very confusing (to me..)

So say you run a 10S1P string per MPPT. So you'll get a good 400V string @ 13A x 2 strings = 10400W. Exactly on the PV max input power.

However, in my mind, the MPPT's max. current = 26A, there one can assume that on can easily run a 10S2P setup per MPPT (400V @ 26A = 10400W), thus totaling 20800W, which does not sound too healthy for the inverter. With losses, it will never get to that, plus the MPPT will clip any excess Current over 26A in any case.

It is a common setup to over panel an Inverter, to compensate for normal losses, as well as for better production during the Winter period, but over paneling with a 10S2P per MPPT, sounds like a stretch, never mind setting free some unforgiving smoke signals.

What say the experts.. how to interpret these number correctly and apply them to installations for benefit?

38 minutes ago, AndreGreyling said:

I have 2 strings with 5 panels each and want to increase one to 8 (545w) panels.
Where can I see if I am using one string per MPPT and not perhaps just one MPPT with 2 strings on it?

Safest is to link to this Status screen off from the home screen, and read the values under "Solar Power" for M1 and M2.

If you are using two strings, then under M1 and M2 you should find similar Voltage of around 200V on each MPPT, and current of somewhere under 13A.

If you are using both strings on one MPPT, then only one of the strings will see the 200V voltage, and current of up to 26A.

1 hour ago, GreenFields said:

Safest is to link to this Status screen off from the home screen, and read the values under "Solar Power" for M1 and M2.

If you are using two strings, then under M1 and M2 you should find similar Voltage of around 200V on each MPPT, and current of somewhere under 13A.

If you are using both strings on one MPPT, then only one of the strings will see the 200V voltage, and current of up to 26A.

Just now, AndreGreyling said:

So I am using both MPPT's with one string each?

1 hour ago, AndreGreyling said:

So I am using both MPPT's with one string each?

Yes, and with that you've got an option of what you want to do, which upgrade path to follow, depending on where you'd like to end up.

As was said, you can safely increase each of your existing strings to 8 panels each, to get a total of 8720W. In this case the PV Input Voltage is the limiting factor. Might be all you need, and if so that's fine.

Otherwise, you could go the route of 5S2P per MPPT, to fit 20 panels, ie. to fit 10900W of panels. In this case the PV Input Current is the limiting factor. Better for if you want to charge more batteries, cater for poorer weather, or end up going more off-grid.

In each case the nameplate Wattage is over the inverter's maximum of 8000W AC power and/or 10400W DC power respectively, but the inverter will just draw what it needs.

Edited June 16, 20251 yr by GreenFields

23 minutes ago, GreenFields said:

Yes, and with that you've got an option of what you want to do, which upgrade path to follow, depending on where you'd like to end up.

As was said, you can safely increase each of your existing strings to 8 panels each, to get a total of 8720W. In this case the PV Input Voltage is the limiting factor. Might be all you need, and if so that's fine.

Otherwise, you could go the route of 5S2P per MPPT, to fit 20 panels, ie. to fit 10900W of panels. In this case the PV Input Current is the limiting factor. Better for if you want to charge more batteries, cater for poorer weather, or end up going more off-grid.

In each case the nameplate Wattage is over the inverter's maximum of 8000W AC power and/or 10400W DC power respectively, but the inverter will just draw what it needs.

Thanks for this fantastic explanation!