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How to best integrate external MPPT with Sunsynk?


wolfandy
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Hi all

I am in the process of upgrading my system from older Axperts to the 8kW Sunsynk and adding some more panels.

Am planning to install 3 strings, each facing a different direction. 2 of the strings will be connected to the MPPTs of the Sunsynk, the 3rd to a Victron MPPT that I already have in my systems.

My question is how to best integrate the Victron MPPT with the Sunsynk?

Currently the MPPT is connected to a DC bus bar together with the Pylontechs and the Battery-In of the Axperts. Do I keep it that way or can I connect the MPPT on the Generator Input of the Sunsynk? What would be advantages/disadvantages?

If I keep the Victron MPPT connected to the DC bus bar, then I cannot use their production to power non-essential loads, correct? How could I connect the Victron MPPT to also use it's production to power non-essential loads?

Thanks in advance for your help
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51 minutes ago, Brani said:

Your Victron MPPT will produce 48V DC. Generator input is 230V AC. 

Fair point. Have to admit that I missed that one 🙄

52 minutes ago, Brani said:

Why not keep the axpert setup with battery and mppt with one string for one set of loads, and use Sunsynk with other 2 strings for another set of loads?

Everything is already wired for a single system. The reason I want to upgrade is mostly (a) to be able to blend PV and grid for cloudy days and (b) to also be able to feed non-essential loads currently purely on grid with excess PV.

Keeping the Axperts would in my view rather complicate my setup

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39 minutes ago, Brani said:

Just an idea... replace it with Victron inverter (Multi or Quattro) and you can keep the mppt, busbar, and batteries. 

Yeah, that was my original idea. But I struggle to justify the cost of 2x Multi, 2x MPT, and GX device compared to the Sunsynk...

I'll still keep the Victron MPPT, DC busbar setup, and my Pylons with the upgrade to the Sunsynk. It just means that the Victron MPPT will only be able to power the essential loads and charge the batteries - but not also feed non-essential loads

Or am I missing anything?

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10 minutes ago, Brani said:

you can’t control the battery with Inverter and mppt at the same time

This does work. My system is set up that way at the moment. The only thing to be careful about is that the max charge amps between the inverter and the MPPT do not exceed the max charge amp of the battery

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14 hours ago, wolfandy said:

Hi all

I am in the process of upgrading my system from older Axperts to the 8kW Sunsynk and adding some more panels.

Am planning to install 3 strings, each facing a different direction. 2 of the strings will be connected to the MPPTs of the Sunsynk, the 3rd to a Victron MPPT that I already have in my systems.

My question is how to best integrate the Victron MPPT with the Sunsynk?

Currently the MPPT is connected to a DC bus bar together with the Pylontechs and the Battery-In of the Axperts. Do I keep it that way or can I connect the MPPT on the Generator Input of the Sunsynk? What would be advantages/disadvantages?

If I keep the Victron MPPT connected to the DC bus bar, then I cannot use their production to power non-essential loads, correct? How could I connect the Victron MPPT to also use it's production to power non-essential loads?

Thanks in advance for your help

The 8k Sunsynk comes with 2x 18A MPPTs capable of handling 4 strings, newer ones are capable of 22A. If there is a noticeable difference in output of all 3 arrays due to orientation, I agree that you may want a third MPPT. You haven't indicated the sizing of your arrays, but if one of them is small then you may want to consider a microinverter connected to the Aux/Gen port. If the array is too large for that, consider a Sunsynk string inverter like the 3k SSUN-3KEXP.
image.png.8279a0e3446ef93d33c1ed696ec7882a.png

You can then flog the Axpert and Victron MPPT to cover the cost (which ought to be far less than the 3k Hybrid Sunsynk).

Alternatively, if you have space on the main two arrays' roof, then consider splitting the 3rd array's panels between the two.

Agreed that you could consider adding additional Victron kit and FrankenMonster it, but that would negate any benefit of going Sunsynk in the first place, and introduce additional points of potential failure.

Edited by YellowTapemeasure
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56 minutes ago, YellowTapemeasure said:

If there is a noticeable difference in output of all 3 arrays due to orientation, I agree that you may want a third MPPT. You haven't indicated the sizing of your arrays, but if one of them is small then you may want to consider a microinverte

Thanks

My plan so far was to split my current 12x 380W panels into 8x on the Sunsynk and 4x on the 250V Victron. Then to add 8x 465W new panels on the Sunsynk.

But browsing a bit more and reading up on @TheoG's install, I think I might follow the same route he took and rather take 2x 5kW Sunsynk in parallel. That way I would have 4x MPPT and could avoid having to run an external MPPT (and sell it). I probably just would need to add at least another 2x 380W panels to make that string more panels to boost the voltage

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5 minutes ago, wolfandy said:

Thanks

My plan so far was to split my current 12x 380W panels into 8x on the Sunsynk and 4x on the 250V Victron. Then to add 8x 465W new panels on the Sunsynk.

But browsing a bit more and reading up on @TheoG's install, I think I might follow the same route he took and rather take 2x 5kW Sunsynk in parallel. That way I would have 4x MPPT and could avoid having to run an external MPPT (and sell it). I probably just would need to add at least another 2x 380W panels to make that string more panels to boost the voltage

Yes, that's another good option. I have 16x 380W panels on my single 5k with 2 MPPTs, works great, and I have capacity for 2 more panels (one on each MPPT) with my North facing install.  

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30 minutes ago, Brani said:

can the Sunsynk battery terminal take a mppt and a busbar

Yes. You connect the battery, the MPPT, and the inverter's battery terminal all to the busbar. The inverter will simply think that the power provided by the MPPT is also coming from the battery 

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3 hours ago, Brani said:

I’m assuming your battery will communicate SOC to the MPPT, and not the inverter? 

My setup is that MPPT is charging based on own manual voltage settings/readings. The Pylon BMS is connected to ICC, which is controlling the inverter based on SOC reading

3 hours ago, Brani said:

When the battery requests the charge, will it come from MPPT or inverter (Eskom or other two MPPT’s) or both?

In my current setup, the battery is not requesting a charge but rather the MPPT deciding that the battery needs to be charged based on voltage readings. I currently do not have any PV connected to my Axpert inverters, so I would only manually charge from grid through them when needed

3 hours ago, Brani said:

And when you limit charge current, won’t you be losing excess solar coming from Victron side? 

This depends on your array sizes. My planning was to fully utilize the Victron MPPT charge current and rather limit on the inverter the max charge current (as it also powers the loads and is less likely to actually provide the max charge current to the batteries)

But for the new system, I think I will rather go the 2x 5kW route instead of the 1x 8kW with external MPPT

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On 2021/05/09 at 12:38 PM, wolfandy said:

Yes. You connect the battery, the MPPT, and the inverter's battery terminal all to the busbar. The inverter will simply think that the power provided by the MPPT is also coming from the battery 

What you are describing is possible in theory, but perhaps a little risky in practice. Battery voltage is not the greatest way to control charge and discharge, there are too many variables (cable length, thickness, heat etc.) that could affect it. The modern way to do it is through comms to the BMS, which reduces the risk to the batteries. 

If it were my setup, I would want to use the Sunsynk's CANbus comms with the Pylontechs to ensure that the Pylontech BMS dictates the charge and discharge rates. You could add the other panels and MPPT to the busbar, but you may still be feeding it charge when it doesn't want it. My personal preference would therefore still be to use a smaller string inverter on the 8k Sunsynk's Aux port, or the two 5k Sunsynks in parallel. It also does not require the ICC, MPPT or Axperts.

Both are simple and clean solutions. Batteries are far too expensive to conduct experiments with, unless you are being paid to do them.

Edited by YellowTapemeasure
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On 2021/05/10 at 6:27 PM, YellowTapemeasure said:

What you are describing is possible in theory, but perhaps a little risky in practice. Battery voltage is not the greatest way to control charge and discharge, there are too many variables (cable length, thickness, heat etc.) that could affect it. The modern way to do it is through comms to the BMS, which reduces the risk to the batteries. 

I've been running this setup without any problems for the last 1.5 years. The Victron's voltage readings seem to be quite accurate, as the BMS (through ICC) reported 100% SOC every time

On 2021/05/10 at 6:27 PM, YellowTapemeasure said:

two 5k Sunsynks in parallel

Yup - that is also what I have now gone for. Managed to change my order from 1x 8kW to 2x 5kW before it got shipped. And selling the Victron made up more than the difference 🙂

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