I have a problem. I have 4k5W of panels in 2 strings feeding an 8kVA Deye inverter and 7.2kWh of Blade battery. I wish to add a further 4kW of panels (and another battery), but do not really require a bigger inverter. the solution is to add a Victron 250/60, say, charger to handle the extra string. Can this work, or will the Deye MPPT throw up it's arms in despair? Is there another solution that the esteemed members of the forum may have up their sleevies?

22 minutes ago, BigC said:

Can this work, or will the Deye MPPT throw up it's arms in despair?

That should work fine, I have not tried it myself... Deye + extra MPPT, but there should be no reason for this lot not to co-exist, the only possible problem may be that you might not be able to use battery comms between inverter and battery, but may have to run Voltage based...

1 hour ago, BigC said:

I have a problem. I have 4k5W of panels in 2 strings feeding an 8kVA Deye inverter and 7.2kWh of Blade battery. I wish to add a further 4kW of panels

I don't understand the existing scenario. What exact panels do you have now and in what configuration? I'm assuming "4k5W" is a typo.

2 dissimilar strings totaling 27 mixed panels, cobbled to give me 2 nice strings of about 4500W total. They were inherited so I did the best I could. They are working well. As @Kalahari Meerkat suggested, I may have to forgo the BMS connection, configure the battery mode as "use battery v" which means I lose some of the battery metrics. Was hoping someone tried this before I spend the bucks . . . 😆

12 minutes ago, BigC said:

2 dissimilar strings totaling 27 mixed panels, cobbled to give me 2 nice strings of about 4500W total. They were inherited so I did the best I could. They are working well. As @Kalahari Meerkat suggested, I may have to forgo the BMS connection, configure the battery mode as "use battery v" which means I lose some of the battery metrics. Was hoping someone tried this before I spend the bucks . . . 😆

I wouldn't do that as a first choice. The inverter can in theory connect up to 10,400W of panels. Now I understand that it's a mixed bag of panels, but I'd start by maybe listing what you've got by make and model of the panels, and then seeing if one can come up with a configuration that could allow you to add that 4kW of panels without resorting to another MPPT. If it's a forlorn hope, if it doesn't work, then so be it, or if you've already gone through the thought process and concluded that you need the MPPT solution, that's something else, but from what you've written, I'd at least ask if this is an option.

6 hours ago, GreenFields said:

if you've already gone through the thought process and concluded that you need the MPPT solution

A Solis grid tie inverter on the Aux port with frequency control is better than a standalone MPPT.

7 hours ago, BigC said:

27 mixed panels, cobbled to give me 2 nice strings of about 4500W

I agree with @GreenFields take proper inventory of the solar panels, how the strings are configured and the reason you want to use a 3rd party Mppt. Above in your response the figures does not make sense. 4500/27= 166w/panel average output?.

How is the 2 strings connected to the Deye are you using both string inputs on Mppt 1 or 1 string/ Mppt. Also the orientation of the 2 strings. What is the motivation for adding the extra panels eg cloud conditions, load coverage, battery charging?

Edited March 7Mar 7 by TaliaB

12 hours ago, BigC said:

I have a problem. I have 4k5W of panels in 2 strings feeding an 8kVA Deye inverter and 7.2kWh of Blade battery. I wish to add a further 4kW of panels (and another battery), but do not really require a bigger inverter. the solution is to add a Victron 250/60, say, charger to handle the extra string. Can this work, or will the Deye MPPT throw up it's arms in despair? Is there another solution that the esteemed members of the forum may have up their sleevies?

Short Answer, Yes! it can work and there is no need to disconnect your BMS. Separate MPPT, separate string will have no interference with your inverter functioning as it should, as this is like connecting an ''extra battery'' on your battery bank

Copied and pasted

Methods for Adding External MPPT to Deye

There are two primary ways to add more solar capacity to an existing Deye installation:

1. Direct-to-Battery (External MPPT/Charge Controller): You install a separate, third-party MPPT charge controller (e.g., Victron SmartSolar) and connect its output directly to your battery bank.

   • Pros: Independent of Deye MPPT limitations; easiest for adding panels with different voltages or orientations.

   • Cons: Requires its own monitoring/app; not directly visible in the Deye Solarman app.

2. AC Coupling (Additional Grid-Tie Inverter): You install an AC-coupled microinverter or string inverter and connect its output to the GEN or GRID port of the Deye inverter.

   • Pros: Fully integrated into Deye monitoring; efficient for large scale expansion.

   • Cons: More complex setup, requires proper grid-tie settings

If I opt to fit a second inverter rather, say a 3.6k or 5k unit, which is a bit more expensive, then you lose nothing .. just as long as they are compatible when connected in parallel. Can one mix inverters, as long as they are from the same stable?

7 minutes ago, BigC said:

If I opt to fit a second inverter rather, say a 3.6k or 5k unit, which is a bit more expensive, then you lose nothing .. just as long as they are compatible when connected in parallel. Can one mix inverters, as long as they are from the same stable?

No, you need to run identical inverters in parallel.

Buying a hybrid inverter and not using with a battery is a waste of money. If you couple both inverters to the batteries, you will have double the losses/own consumption.

@GreenFields . . . Just to clarify, the existing panels are old and were installed on 3 different occasions, as 3 strings, on a roof that is impossible for me to access. The cables all ended up in the garage, where I was able to measure OC voltage and SC current, and then carefully connected the panel sets that were identical in current, at least, into 2 strings. It is not possible to identify them, or change the configuration.
@frivan and @hoohloc have identified a possible solution. I have 3 x Solis mini 2500 inverters (removed from the old installation)! However, I don't see how they can connect to the Aux/Gen port. Surely the grid-tie inverter needs to see a grid? Would the Gen port work like that?

18 minutes ago, BigC said:

I have 3 x Solis mini 2500 inverters (removed from the old installation)! However, I don't see how they can connect to the Aux/Gen port. Surely the grid-tie inverter needs to see a grid? Would the Gen port work like that?

Yes, this is the AC coupling method as described above, and I guess you can read more about in the manual of the Deye under the Grid/Aux port operating modes. Basically the Deye inverter acts as a controller and creates a mini-grid. The Solis inverter will respond to the grid signal from the Deye, generate power and the Deye inverter will then charge the battery connected as normal.

I love this solution .. now to commence the install. Thank you all for your valuable contribution to my enquiry. All done and dusted in < 12 hours. I just enjoy this forum . . . 🙂

PS . . . I may need help with the configuration, but will cross that bridge when I get there. Ciao . . .

3 hours ago, BigC said:

@GreenFields . . . Just to clarify, the existing panels are old and were installed on 3 different occasions, as 3 strings, on a roof that is impossible for me to access.

So how are you going to install the new panels if it is impossible to access the roof?

Even if you need to pay an installer just to survey your existing panels that would still be money spent wisely - at least in my opinion... You might possibly be able to remove some of the least powerful existing panels, and just replace them if the support is adequate, thereby saving some installation costs.The cables all ended up in the garage, where I was able to measure OC voltage and SC current, and then carefully connected the panel sets that were identical in current, at least, into 2 strings. It is not possible to identify them, or change the configuration.

4 hours ago, frivan said:

Buying a hybrid inverter and not using with a battery is a waste of money. If you couple both inverters to the batteries, you will have double the losses/own consumption.

Wise words - I agree.

22 hours ago, BigC said:

@GreenFields . . . Just to clarify, the existing panels are old and were installed on 3 different occasions, as 3 strings, on a roof that is impossible for me to access. The cables all ended up in the garage, where I was able to measure OC voltage and SC current, and then carefully connected the panel sets that were identical in current, at least, into 2 strings. It is not possible to identify them, or change the configuration.
@frivan and @hoohloc have identified a possible solution. I have 3 x Solis mini 2500 inverters (removed from the old installation)! However, I don't see how they can connect to the Aux/Gen port. Surely the grid-tie inverter needs to see a grid? Would the Gen port work like that?

Hi @BigC - just to get back to this - and it comes back to understanding the existing configuration before making decisions. I'm understanding from the above that you had 3 strings, one on each Solis mini 2500. That means each string will have been with a max input current of 11A, and a max power rating of 2500W.

I'm also understanding that you managed to combine 2 strings onto one MPPT of the Deye, and that you connected the other string to the second MPPT. You don't want to make changes to the strings on the roof, but you have access to the cables in the garage.

If this is all correct, then the logical thing for me would be to connect the single string off from the second Deye MPPT, and connect it back to your Solis 4G again (this time with the Solis inverter connected via the AUX input). This will free up the MPPT on the Deye that can take a 5200W string at least.

Is this what you were thinking of doing anyway? Also, sorry to bug and beat this drum, but these things stick in my head and then bother me.

@GreenFields Very well assumed as I also understand the actual wiring. All well indicated. As a ex used ofthe Solis mini for 5 yrs before my Deye I agree on your whole input and a great input for other that would like to use a Solis mini. This is a cheap way of using a external MPPT via AC coupling. 2nd hand these Solis inverters are very cheap.

@HennieL : The garage roof is fully utilised and additionally not optimised for angle, etc. Additionally, the cables and panels were installed in clusters (don't understand why). The new panels will go on the house roof. I would have preferred to mount the Solis in the house and run a mains cable to the garage, but the configuration suggested below works much better .. will have to run PV cable to the garage instead . . .

Thankyou @Scorp007 and @GreenFields .. "If this is all correct, then the logical thing for me would be to connect the single string off from the second Deye MPPT, and connect it back to your Solis 4G again (this time with the Solis inverter connected via the AUX input). This will free up the MPPT on the Deye that can take a 5200W string at least". That is the conclusion I came to. I spent some time on ChatGPT exploring all this.

The result is 4.1kW (9 panels at 460W) + 2.6kW on the Deye and 2.9kW on the Solis giving me 9.6kW total. This is close to the 190A max charging current. I think this is as good as it gets. ChatGPT suggests keeping the Gen port input substantially lower than the onboard MPPT input as, it seems, the Solis responds more slowly to the frequency shift generated by the Deye and this can cause hunting. Thankyou all for your wonderful and knowledgeable contribution to this thread. I have confidence now that this will work .. can't wait to implement this upgrade. Ciao . . .

6 hours ago, BigC said:

@HennieL : The garage roof is fully utilised and additionally not optimised for angle, etc. Additionally, the cables and panels were installed in clusters (don't understand why). The new panels will go on the house roof. I would have preferred to mount the Solis in the house and run a mains cable to the garage, but the configuration suggested below works much better .. will have to run PV cable to the garage instead . . .

Thankyou @Scorp007 and @GreenFields .. "If this is all correct, then the logical thing for me would be to connect the single string off from the second Deye MPPT, and connect it back to your Solis 4G again (this time with the Solis inverter connected via the AUX input). This will free up the MPPT on the Deye that can take a 5200W string at least". That is the conclusion I came to. I spent some time on ChatGPT exploring all this.

The result is 4.1kW (9 panels at 460W) + 2.6kW on the Deye and 2.9kW on the Solis giving me 9.6kW total. This is close to the 190A max charging current. I think this is as good as it gets. ChatGPT suggests keeping the Gen port input substantially lower than the onboard MPPT input as, it seems, the Solis responds more slowly to the frequency shift generated by the Deye and this can cause hunting. Thankyou all for your wonderful and knowledgeable contribution to this thread. I have confidence now that this will work .. can't wait to implement this upgrade. Ciao . . .

Yes the Solis mini is much slower due to its vintage than the current range of inverters.

The aux input is a great feature of the current tech in inverters.

Illness, weather, installation of 9 x 460W panels, and the addition of another Blade battery have delayed the commissioning of the system somewhat. However, it is all working well .. I got rather excited .. up to the point of the batteries reaching 100% SOC. Sadly the inverter does not react to this situation by increasing the frequency on the Gen port. Hence, at some point the inverter turns off the supply to the Solis with alarms sounding and all manner of consternation. The faults logged by the Solis are consistently "disconnected from the grid" It would seem that this Deye has older FW .. Ver 0-5388-1516, which does not implement this means of regulating the Gen port output.

Additionally, I have no experience of the Solis inverter and the configuration seems a nightmare. I therefore have no idea whether its present configuration is suitable. First off I suppose I can lean on Deye support to download the latest FW .. is this a no risk scenario?

I'm not sure if the Deye settings & names are exactly the same as the Sunsynk (they are the same inverter hardware...), but the Sunsynk's Aux Port (also used for generator) has a dedicated "tab" with various check boxes. In this Aux load / Gen window one can either select "Aux load output", "Gen input", or "For micro inverter input". Make sure that you do not inadvertently have the "Aux load output" ticked - given that your Solis is another inverter, the logical guess would be the "For micro inverter input" box to be ticked.

7 hours ago, BigC said:

The faults logged by the Solis are consistently "disconnected from the grid"

This might be (guessing) that the Deye cannot see the Gen input" if it is configured to be an "Aux load output" ...

Thanks for your comments. The Deye does make this distinction with a tick box. Earlier today the Deye FW was updated, so I am hoping to see a change tomorrow. Additionally I will be assisted tomorrow by Solis to verify it's settings as well . . . 😀