want to run 2 strings on one MPPT

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mufaddalk

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I have a string of 10 panels in NE direction connected to myMPPT that charges my 48V battery. (running a PIP5048GK MPPT/INVERTER all in one)

I would like to have another string of 10 in NW direction. I cant parallel them obviously as they are in different directions.

My questions, is there such a thing as automatic dc transfer switch that i can buy (best option) or if not build that will allow me to switch from one string to the other at the point where it feed to the MPPT. If it can switch automatically based on current i.e. the string at has the max current or even based on timer i.e. i can program it based on the time of the day i need to switch the string.

If there is an alternate option please let me know. If this has been asked before i apologize.

Thanks
 
Actually, you can parallel them.
You may want to add an inline diode into each string, to prevent current from the sunny string reversing into the other in the shade. There are neat units integrated into MC4 connectors. You might get away without one if both sides get enough ambient light.
And of course, the combined cable must be thick enough to carry double the current.

But depending on the intelligence of the MPPT, and the exact position of the sun / clouds, you may not get as much power as when having 2 separate MPPTs. It's possible that some times one string won't contribute at all.
 
Thanks ajw22, how would the circuit be? a diode or a mc4 connected at each end of string and join them before connectiong to mppt? sorry i am a noob
 
If you have 10 panels in series, that's some serious voltage that could easily kill you. If you're even slightly unsure about it, don't do it.
It should not need saying, but if you're not a professional,do it after dark and wear insulation gloves, just in case.


Something like this would be convenient to use:
https://www.aliexpress.com/item/32903440367.html

Inside is basically a diode like this that allows current to flow only in one direction. In this use, it's often referred to as a blocking diode. The silver marking on the one end shows thedirection of flow.
https://www.aliexpress.com/item/32880775284.html


This would be one possible circuit. You can place the diodes just as well on the negative side, or even between the panels.
Again, you may not need it. But it's not wrong to use it.

image_nervpe.jpg
 
Its better to parallel them since that will gove more overall BUT best is of course to just buy another MPPT charger like an PCM60x and you get even more energy.
 
you just need a parallel combiner box - I have 3 parallel strings of 4 panels - I use a midnite solar combiner on the roof then run a single bit of 2 core down to the MPPT controller.

All modern panels have reverse protection diodes built in.
 
HughF said:
All modern panels have reverse protection diodes built in.
Click to expand...

No, they do not.This is a common misunderstanding. Virtually all large panels made in the last ~10 years or so have severalbypass diodes, which are not the same as reverse protection diodes. It may be the same device, but is wired in differently to serve a very different function.Bypass diodes are there to split a panel into typically 3 sections, andallow each to bebypassed individually.
Without these diodes, a single leaf covering just one cell would kill the output of the whole string to virtually zero.
With these diodes, that same leaf would disable the output ofjust1/3 of a panel, and the rest of the string will keep producing.

Some smaller panels designed to directly attach to batteriesmay have reverse protection diodes built in.


Found some SMA documentation on using multiple strings:
https://www.sma-italia.com/fileadmi...dium_Power_Solutions/Rueckstrom-UEN083010.pdf
 
thanks ajw22 for the circuit diagram. the connection seems simple enough.

the mc4 connectors with inbuilt diodes have negligible cost compared to new mppt. efficiency is not an issue as i have more than enough panels then required for my battery.

thanks all for your inputs
 
You might find this youtube interesting by @Adam Welch "Solar Panel Shading"
It goes into a detailed explanation and actual experiment related to @ajw22's comments and shading/reverse current in a string of panels. :)
 
OffGridInTheCity said:
You might find this youtube interesting by @Adam Welch "Solar Panel Shading"
It goes into a detailed explanation and actual experiment related to @ajw22's comments and shading/reverse current in a string of panels. :)
Click to expand...


Interesting indeed. Always nice to see practical tests confirm or correctthe theoretical.

Some notes to the video relating to the original thread question:
The 0.2V~0.5Vloss caused by the reverse blocking diode is negligible in an string application with 300+V.
The MOSFET "ideal diode" module is designed to handle much lower voltages. Very likely to blow up in a stringapplication.
 
I would like to know what the panel specs are and also what the mppt can handle. That is required to give the man a proper answer I would say. That is besides the fact that all this talking about diodes is not necessary since you don't need them when you parallel 2 strings even though they are not orientated the same.
 
"The effect of reversely induced electric stress currents has demonstrated to be a very important factor in determining not only the performance and efficiency of PV solar cells and modules, but it has also proven to be a dominant factor in determining the operating lifetime of the cells."
View attachment 6
 

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