Connecting different voltage PV strings in parallel?

chewface

New Member
Joined
Sep 17, 2021
Messages
4
Hi Fellow Solar-ites!
I have an odd number (15) of panels and have connected them in series as 2 separate strings (8 and 7 panels). Can I connect these in parallel? If so, does this result in the amount of current generated being limited to the smaller (7 panel) string?

BTW the panels are all the same brand (Trina) and rating (450w).

I have tried to find an answer on the internet, but all of the articles I’ve found relate to connecting different voltage panels in parallel, not strings of panels.


Would appreciate some expert guidance on this, so I can figure out if it makes any sense to proceed with this approach.

Thanks
 

Roswell Bob

Solar Addict
Joined
Dec 5, 2020
Messages
743
Location
Warner, NH
Can you deal with 2 strings of 7 and use the extra panel some other place? Sorry to answer a question with another question.
 

time2roll

Photon Sorcerer
Joined
Mar 20, 2021
Messages
3,871
The mismatched voltage will have the MPPT select a voltage that is not optimal for either set and reduce production significantly.
I would switch to 7s2p or 5s3p or add one more panel for 8s2p.
 

MichaelK

Photon Sorcerer
Joined
Mar 21, 2020
Messages
2,296
I started out with 15 panels, and wired them as 3S5P. Has worked happily for years now. What are the voltage limits of your particular controller (low and high)? You could go with either 3S5P, or 5S3P depending on what those are?

BTW, know that when you have more at least 3 parallel strings of panels, it is a code requirement to have them protected via a fuse or a breaker. Fuses are cheap, but breakers are more convenient. I use a Midnight 6-breaker combiner box to hold my string breakers.

As a general rule of thumb, string voltages should not vary by more then 5% for the controller to be happy.
 
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