diy solar

diy solar

Connecting different voltage PV strings in parallel?

chewface

New Member
Joined
Sep 17, 2021
Messages
6
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
 
Can you deal with 2 strings of 7 and use the extra panel some other place? Sorry to answer a question with another question.
 
Check out this set of videos from Alt-e.


If it was me, I would do like Bob said above and go with balanced strings of 7.
 
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.
 
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.
 
I have currently 3 strings (304v, 312v, 475v) when connected to a Fronius grid-tied inverter (3 strings in and 3 phases out)
These strings were installed by a professional team that used lots of silicone rubber ;)
I want to connect all three together using breakers and use them as input to a Growatt DLP5000ES which has a max DC Open Circuit voltage of 450V DC for input.
My hope is that in overcast weather I can use all three strings for the Growatt. In full sunshine I hope I can divert some strings (using breakers) to the Fronius for export to the grid.
Any advice welcome.
Should I expect 312v combined with 475v to be below the 450V DC limit?
 
Back
Top