Multiple mppt chargers for different strings

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dylan-hyslop asked Dec 6, '21

Multiple mppt chargers for different strings

Good day,

My house has got lots of small roofs all facing in different directions, We also have a lot of trees with a lot of shading going on at different places at different times in the day.

I have some crazy ideas that I want to run past you guys, to see A: is it possible and B is it advisable?

Can I run 4 to 6 different arrays all with their own mppt charger onto the 48V dc bus? (Single Lithium Battery)

The arrays will probably differ in size and will also possibly provide power at different times in the day?

Here is a rough summary of the arrays, all using 350w panels: (panels are not bought yet, so I can get whatever is recommended).

6 panels facing north
3 panels facing west (afternoon sun)
6 panels facing east (morning sun)
4 panels facing northish (with shading in the afternoon)
TBC
TBC

I will try and keep each array in the same shading area as much as possible to try and prevent shading on a particular string.

This is obviously not going to be the most economical (cost-wise) way to do this, as there will have to be multiple cable runs and 4 to 6 mppt chargers vs one large one.

I am hoping this will help modularise the system and most importantly allow the mppt tracking to work for each string optimally as they get different amounts of sun/shade throughout the day.

MPPT Controllers mppt charging

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Answer 1 · 2021-12-06T12:56:53Z

JohnC answered · Dec 06, 2021 at 12:56 PM

Hi @Dylan Hyslop

It's possible to do it, but you may not find it worthwhile. Both for the added cost and the benefit derived. For example, if you have plenty of sun and your batts are charged early, then it doesn't matter if shade happens. And if it's full cloud the the strings will tend to equalize the tracked V anyway.

Other little things impinge too. Eg. The 4x panel block. You don't mention panel V or battery V, but you should be on 48V. 2x panels per string will likely be too low a tracked V under shade to function, and 4x in a single string would mean an expensive oversized 250/60. And that for a time you rarely need it anyway. (Under shade my own panels drop tracked V from like (nameplate) 105 Vmp to as low as 60V).

Summer vs Winter is important, and in SA anything facing north you'll treasure, but even then I've found that most panels will track to a similar V if they're not totally shaded by their own tilt angle.

Just me, but I'd probably choose a single 150/100 and run 3x panels per string, so 6x strings (1x panel deleted from the northish string).

But I'd run each of your 4 orientations on separate wire pairs to enable testing. If you decide on the 'TBC' arrays then you'd need more mppt anyway, so you could switch around as desired.

Just my view on it.. have fun choosing.

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dylan-hyslop commented · May 31, 2022 at 05:34 AM

That's this does make sense. I'm just struggling with the voltages. I find the victron mppt 150V range does not work very well with modern larger panels. as running two in series the shaded voltage is 2 low, and 3 in series the VOC is just slightly 2 high. And as you said upgrading to a 250v unit just for a few volts don't be VOC is not worth the money.

I have started with the best facing array. With 6 panels. the idea is to start with 3 strings of 2 panels. But I suspect the shaded voltages will be too low. Look this is better than a VOC that is too high as it wont cause any permanent damage. Hopefully, the mppt will do it job and keep the Volts up.

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