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lcollis avatar image
lcollis asked

8kw mppt controller options

Kia ora from New Zealand!

Needing some help. We've previously been offgrid but went for the 5kw easy solar which made this whole process much simpler but 5kw inverter isn't going to work for our next place. Too bad they don't make an 8kw easy solar! We're aiming to have a 8kw array and 8kw inverter.


Anyway, I need a second opinion incase I'm missing something and some advice.


Here's the plan:

- 2x smartsolar mppt 250/100-tr ve.can charge controllers

- 20x 420w Longi panels 10 on each charge controller with 2 strings (5 in each)

- QUATTRO 48/8000/110-100/100 230V VE.BUS INV./CH.

- 5x pylon tech us300 batteries

- color control gx


Is this a smart, most simple and economical way do to this with victron gear? Am I on track here?

Is there a better way other than running 2 solar controllers?

I've seen people using shunts. What's a shunt, is it necessary? (we haven't used one on our previous system).

Anything else that I should be aware of or that I'm missing?

MPPT Controllersoffgrid
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3 Answers
snoobler avatar image
snoobler answered ·

If those panels are 60 cell (Voc 37-40V-ish), 5S is fine. If those are 72 cell panels (Voc 46V+), 5S is too close to 250V, and you should go for 4S. Insure the array short circuit current does not exceed the PV input current limit (IIRC, it's 70A).


Comments:

  • Owning a CCGX myself, I wish I had a Cerbo. Recommend you get a Cerbo. If you plan to use the VE.Can of the MPPT to synch the chargers and connect to the GX, you MUST get a Cerbo for the BMS connection. VE.CAN can be used for BMS, but it can't also be used to connected to the MPPT. You'll need the Cerbo for the BMS.CAN for the Pylontech connection and VE.CAN for the MPPT.
  • You could go up to about 12kW with a single RS450/200 charge controller.
  • Shunts - I believe the EasySolar had this built in - it's what reported % charge.
  • IMHO, due to limitations of the Pylontech implementation, I would recommend a BMV-712 or Smartshunt if for no other reason to pass accurate voltage information to the MPPT in a VE.Smart (bluetooth) network. The Pylontech does not pass shared voltage to other system components.
  • Make sure you get 3 VE.Direct cables and a 32GB MicroSD card for the Cerbo data logger.




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kevgermany avatar image kevgermany ♦♦ commented ·
Sadly no shunts in easysolar.
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lcollis avatar image
lcollis answered ·

Thanks for the info there. Some good advice. Will definitely go with the cerbo.

After looking at the new 450 mppt controllers I was put off by the price of the 200 but the 100 seems doable! I am considering going for the 450/100 mppt charge controller and going with 2 strings at 4kw each at different angles. (our house is a boomerang shaped house so this would work well). One facing north and another facing north west. Thoughts?


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snoobler avatar image snoobler commented ·

The 450/100 is limited to about 5760W, so the 4kW on different orientations would help you utilize more of the array.


1681757011583.png


With it's higher Voc allowance, it as a notably lower PV current allowance than the 250/100. Getting 10S on a string may not be practical.

Link to your panel's datasheet?



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1681757011583.png (57.2 KiB)
lcollis avatar image lcollis snoobler commented ·

https://drive.google.com/file/d/1n_ZHkY5sq5oijtLQ7jTmIqmQtjrkELH0/view?usp=drivesdk

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snoobler avatar image
snoobler answered ·

Thank you. That's a first for me. Those are 54 cell panels but have the Voc of 60 cell panels.

I just wanted to confirm that 10S was do-able with those panels. You're at ~380Voc and ~14A Isc. A single string of 10 is fine. If it never gets below -3°C at your location, you could go 11S :)

Looking back at your original plan of 2X 250/100, you could safely go 6S down to -11°C, but 5S would be more practical with 20 panels and give an absurdly large temperature marggin. 4P would stay within the 70A PV input limit. Two of these controllers would capture all of your array. You could even downsize to 2X 250/70 for about the same price as a 450/100, so 5S2P on each controller - well within all limits and not failing to convert available photons to electrons.

As awesome as the 450/100 is, I don't know that it's the best solution for you. When looking at replacing 2X 250/100, it made more sense but realizing you could capture everything you have with 2X 250/70, that would be my inclination.


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lcollis avatar image lcollis commented ·

Oh, that's a better option! That's why it's great to run ideas past others. Much appreciated. Thank you

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snoobler avatar image snoobler lcollis commented ·
Glad to hear it! Definitely get the Cerbo for the added VE.Direct ports.
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lcollis avatar image lcollis snoobler commented ·
Can I just ask one more question. I'm off grid, won't ever be tied to the grid and will have a generator back up that I'm planning on programming in to start when the batteries hit a certain percentage. Knowing this as it a better move to go with the multiplus ii 8kw rather than the quattro?
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snoobler avatar image snoobler lcollis commented ·

I have 2X Quattro in parallel for 120/240VAC/60Hz split phase power in the U.S.


I too am off grid with genny backup. The ONLY reason I selected Quattros was because of the lack of availability of a 48/5000 120VAC Multiplus at the time of purchase, and I didn't want to go the autotransformer route with a 230V unit. I see having two Quattros as backup. Both won't fail at the same time, right? :)


Even without the second AC input, one can always make provisions for a second AC source with a transfer switch to select back and forth.


Even now, the max 48V MP-II is 3000 for 120VAC. If a MP-II 48/5000 had been available in 2019, I would have gone that route without hesitation.


I'm looking at your battery capacity... Are those the 3.5kWh Pylontechs? If so, that's only 17.5kWh of storage, and that feels mismatched to 8kW of PV. My Solar is exception in Arizona high desert with 18-21kWh available from a 3kW array. My final array will be 6kW producing up to 42kwh Spring, summer, fall and over 30kW on clear winter says. those values dictate my target usage of 30kWh daily. My battery is sized to allow 36 hours with no charging (45kWh).


Yes, I realize I'm applying my bloated American consumption to your situation, and you may have deliberately oversized your array to account for lower latitude (I'm at 34°N) and weather impacts, but I thought I'd point it out. If you've sized your PV and battery according to your energy needs based on a detailed audit, you're good.


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