MPPT's in parallel

[intrinsicaly]

Hi Martin,
I hope all is well.
Thanks for all your work on this project to date.
Would there be any issues if I put these mppt's in parallel?
I am looking at setting up a 24v lithium battery at either 280A or 560A/hr so I am want to put up to 2kw of panels on the roof.
Based on the specs of the mppt and the solar panels that I have, I can only have two panels in parallel/mppt so I would need up to 5 of these mppt's. Is this feasible?
The panel spec's are as follows;
Voc - 45.84V
Isc - 5.70A
Vmpp - 36.97V
Impp - 5.41A
This setup will be around 17A so will be close to the 20A issue that you have described in another issue. Do you forsee this as an issue as the mppt will spend a lot of the day at this value?

Thanks again for all your work.

Cheers

[martinjaeger]

Hi @intrinsicaly,

Yes, in general it is feasible to put multiple MPPTs in parallel. However, due to voltage measurement tolerances, their charging algorithms could behave slightly different, which may lead to issues because they switch from one charging mode to another at different times. This would be more severe for Lead-Acid batteries than for Li-ion batteries, though.

We did an experiment a while ago to control multiple MPPTs in parallel using CAN for exchanging control parameters. The important CAN part can be seen here. The basic idea is that the node with the lowest node address automatically becomes the master and the others take the master's MPPT algorithm current as their target current. This worked well in the lab, but we haven't been able to test it any further in the field.

Long story short: I would just try it out, it should even work without communication for your setup with a Li-ion battery.

Regarding the current close to 20A: This could indeed be an issue. You could limit the current to 15A by software for the 24V battery. Just adjust the value in the devicetree file.