Unequal Dual Strings on single MPPT

[mmichael]

Dear All,
I would like your expert views on this matter. I now have a Growatt 3000TL inverter which is Single MPPT & Dual string. On one string there are 12 Jetion 245W panels probably in series. The system is 10-years old. The last 2 years I installed the wifi module and noticed that my system never propduces full estimated power and on a good day I am getting 14-15KWHrs whereas others I talk to get much more. I live in Cyprus and we have 300 days of Sun but very Hot and Long Summers. During summer period, my inverter never exceeds 2KW peak production. According to the Shinephone app (growatt mobile app) PV1 (string 1 I assume) operates around 300V.
Is there a way of increasing my total production per day by creating a second string with 3-4 panels pointing either at the same or different direction to avoid exceeding the 3KW limit (like EW)?
I want to increase my daily PV production without replacing existing panels which I presume are not of the best quality!
I attach screeshots from my mobile app of todays production. Weather is sunny with 20 degrees celcius (it is supposed to be winter!)!

TIA,
Michael.

 

[sunshine_eggo]

First, find out how your array is actually wired. "Probably in series" doesn't build confidence.

Vmp needs to be within about 10% or you run the risk of the higher voltage string short circuiting into the lower voltage string.

Your MPPT also required a 120Vmp minimum for MPPT operation. 3 panels won't make it and 4 is probably not enough in warm temps.

12S on your current MPPT is good down to about -9°C.

According to the datasheet you linked, it is a dual MPPT unit, so you could add a second string of 5+ panels for additional power.

Alternatively, you could split your 12S array into a 6S2P array and add additional panels to each string, i.e., 8S2P

 

[mmichael]

First, find out how your array is actually wired. "Probably in series" doesn't build confidence.

Vmp needs to be within about 10% or you run the risk of the higher voltage string short circuiting into the lower voltage string.

Your MPPT also required a 120Vmp minimum for MPPT operation. 3 panels won't make it and 4 is probably not enough in warm temps.

12S on your current MPPT is good down to about -9°C.

According to the datasheet you linked, it is a dual MPPT unit, so you could add a second string of 5+ panels for additional power.

Alternatively, you could split your 12S array into a 6S2P array and add additional panels to each string, i.e., 8S2P

Hello and thanks for your reply. Just a question. Are you sure my inverter is dual MPPT? From the description it says Number of MPPT trackers/Strings per tracker and says 1/2. If it is dual MPPT then I can use 4 Jinko JKM410M-72H which have Vmp42.3V and in series they will be more than adequate for the 150V start voltage requirement of the inverter. What do you think? Am I getting it wrong?
The thing is that I was quoted from a company to install 4 Panels and I want to be sure that if I go ahead it will work OK.
Michael.

 

[sunshine_eggo]

You are correct. I misread it.

Thus all strings must be the same Vmp, so if you want to add more PV, it would make more sense to split your 12S to 2P and add panels per string such as 8S2P.