Hello experts

I have 2 Mecer SOL-I-AX-5P inverters connected in parallel each with their own incoming PV string from 2 strings of 12 JA Solar 330W panels. These are connected to 8 Pylontech US3000 3.6Kwh batteries and then to my DB board.

This is a totally off grid system and has been working great.

I have now purchased a Mecer SOL-I-AX-11M which will have 2 strings of 10 Mecer 545W SOL-P-M-545 PVs coming into the 2 MPPTs.

This will be connected to 8 Pylontech batteries also US3000 3.6Kwh batteries.

My questions are:

1. Is there any way to connect the new inverter in parallel with the other 2 to create one system? My instinct says no because they are not exactly the same inverters? (But I would truly love to be wrong!).

2. If this cannot be done, is there any way to combine the two systems’ AC outputs into my DB board?

I have a feeling my lovely wife is not going to be happy that I didn’t know these answers before we spent the money!!

Thank you

I stand to be corrected, although I do not think you'd be able to run the 3 inverters in parallel and I don't think you'd be able to combine the AC outputs in your DB board.

Perhaps consider selling the 2x 5KW inverter and buying a 2nd 11KW inverter if you want to have it all running as a single system?

 

Although 22KW of inverter power is quite a lot for the average household. I assume it is more the additional panels which you want to be able to add to the system?

I cannot find the current (amps) limit for the MPPT's, although with 20x 545W panels you're basically maxing out the MPPT wattage limit anyways so one would need to look at an additional inverter for additional PV.

 

if I misunderstood and you have 10x 545W Mecer panels and wanted to split them into 2x strings of 5 panels then you could maybe look at running a string of 10 panels (possibly 5S2P) and then add the JA panels on the other MPPT on the 11KW inverter.

15 hours ago, Deonbayly said:

1. Is there any way to connect the new inverter in parallel with the other 2 to create one system? My instinct says no because they are not exactly the same inverters? (But I would truly love to be wrong!).

Definitely not. Paralleling these inverters requires the same battery (all battery modules in parallel), and identical firmware on each. This is simply not possible with the different models.

15 hours ago, Deonbayly said:

2. If this cannot be done, is there any way to combine the two systems’ AC outputs into my DB board?

I guess what you could try is connecting the 11 kW inverter's output to the AC inputs of the other two. So the other two will power the house (to a maximum of 10 kW), then when that battery runs low, it will switch to AC-in, which will be the 11 kW inverter. You can then run the house to a maximum of 11 kW.

Really, the 11 kW inverter doesn't do much, apart from charging half the total battery.

The other thing is to put some loads (perhaps the larger loads) on the 11 kW inverter, while still connecting the AC-out of it to the AC-in of the 5 kW inverters. Then you can run a higher total load, but when the battery for the 2 5 kW inverters runs out, then the 11 kW inverter will be the limit. Having to be aware of this difference could be a problem.

Finally, you could simply split the loads and not connect the two systems in any way. That way, you don't have to worry about overloading the 11 kW inverter with loads from the other inverters, but you could have capacity in one battery when the other is empty. Maybe you could have a changeover switch for any really essential loads, so if one battery goes flat when the other has charge, you can at least switch over those very essential loads to the battery that has charge.

To make a true 22 kW system, you would indeed have to sell the two 5 kW inverters, get another 11 kW inverter exactly the same as the existing one, set up the paralleling boards (the ones you have now should work). You may have to rewire your panels. But in addition, you also have to parallel all your battery modules. So you'd need a decent pair of bus bars for that. You'd be paralleling new modules with older modules, which is always tricky. At the very least, get both battery banks to the same SoC (preferably 100% SoC) before paralleling. Otherwise, you'll have no end of problems with balancing. If the older Pylontechs aren't too old (say 2 years or so), then this should work OK, as far as I know. I think you need some extra hardware to parallel more than 8 Pylontech battery modules; I have no knowledge of that.

Edit: BTW, 22 kW at 230 V is 96 A, so you'll need some serious AC wiring to make that safe, possibly more than 16 mm². But I suspect you won't need that much power all at once.

Edit 2: Another possibility, if 11 kW is enough. Still parallel all the battery modules, but only use the 5 kW inverters as solar battery chargers. They could also be a backup in case the 11 kW inverter has a problem. You could leave them paralleled, but turn the load switches off to save idle consumption. (The switches are really load (AC-out) switches, not total power switches). The inverters should turn themselves off at night, and power up in the morning. If needed, change the load from the 11 kW to the two 5 kW inverters and turn the latter on.

Edited November 2, 20232 yr by Coulomb

Maybe split the loads onto sub-db's, use the MKS inverters to power loads that run mainly at night, lights and kitchen. Use the newer inverter to run plugs and the geyser and basically daytime loads. Just don't tell.

3 hours ago, GreenFields said:

Maybe split the loads onto sub-db's, use the MKS inverters to power loads that run mainly at night, lights and kitchen. Use the newer inverter to run plugs and the geyser and basically daytime loads. Just don't tell.

 

5 hours ago, Coulomb said:

Definitely not. Paralleling these inverters requires the same battery (all battery modules in parallel), and identical firmware on each. This is simply not possible with the different models.

I guess what you could try is connecting the 11 kW inverter's output to the AC inputs of the other two. So the other two will power the house (to a maximum of 10 kW), then when that battery runs low, it will switch to AC-in, which will be the 11 kW inverter. You can then run the house to a maximum of 11 kW.

Really, the 11 kW inverter doesn't do much, apart from charging half the total battery.

The other thing is to put some loads (perhaps the larger loads) on the 11 kW inverter, while still connecting the AC-out of it to the AC-in of the 5 kW inverters. Then you can run a higher total load, but when the battery for the 2 5 kW inverters runs out, then the 11 kW inverter will be the limit. Having to be aware of this difference could be a problem.

Finally, you could simply split the loads and not connect the two systems in any way. That way, you don't have to worry about overloading the 11 kW inverter with loads from the other inverters, but you could have capacity in one battery when the other is empty. Maybe you could have a changeover switch for any really essential loads, so if one battery goes flat when the other has charge, you can at least switch over those very essential loads to the battery that has charge.

To make a true 22 kW system, you would indeed have to sell the two 5 kW inverters, get another 11 kW inverter exactly the same as the existing one, set up the paralleling boards (the ones you have now should work). You may have to rewire your panels. But in addition, you also have to parallel all your battery modules. So you'd need a decent pair of bus bars for that. You'd be paralleling new modules with older modules, which is always tricky. At the very least, get both battery banks to the same SoC (preferably 100% SoC) before paralleling. Otherwise, you'll have no end of problems with balancing. If the older Pylontechs aren't too old (say 2 years or so), then this should work OK, as far as I know. I think you need some extra hardware to parallel more than 8 Pylontech battery modules; I have no knowledge of that.

Edit: BTW, 22 kW at 230 V is 96 A, so you'll need some serious AC wiring to make that safe, possibly more than 16 mm². But I suspect you won't need that much power all at once.

Edit 2: Another possibility, if 11 kW is enough. Still parallel all the battery modules, but only use the 5 kW inverters as solar battery chargers. They could also be a backup in case the 11 kW inverter has a problem. You could leave them paralleled, but turn the load switches off to save idle consumption. (The switches are really load (AC-out) switches, not total power switches). The inverters should turn themselves off at night, and power up in the morning. If needed, change the load from the 11 kW to the two 5 kW inverters and turn the latter on.

Wow! Appreciate your time and advice immensely. There's a lot of food for thought here, maybe all is not lost! Thank you very much! I buy you a coffee!

3 hours ago, GreenFields said:

Maybe split the loads onto sub-db's, use the MKS inverters to power loads that run mainly at night, lights and kitchen. Use the newer inverter to run plugs and the geyser and basically daytime loads. Just don't tell.

Thank you Greenfields, I hadn't thought of that option. Its a little complicated but certainly an option. Appreciate it!

@Deonbayly

I would use existing db and just rewire a split between the 10kw(2x5kw) and 11kw inverters. Split the live and neutrals and decide which supply you want the essential loads then use a transfer switch that can switch between essential on both supplies( inverters either 10kw or 11kw) should you have a problem with one supply. Ensure that the 2 supplies have seperate input and output mcb's and seperate output Rcd's.

Edited November 2, 20232 yr by TaliaB

4 hours ago, TaliaB said:

@Deonbayly

I would use existing db and just rewire a split between the 10kw(2x5kw) and 11kw inverters. Split the live and neutrals and decide which supply you want the essential loads then use a transfer switch that can switch between essential on both supplies( inverters either 10kw or 11kw) should you have a problem with one supply. Ensure that the 2 supplies have seperate input and output mcb's and seperate output Rcd's.

Thank you very much! Another option to consider. Much appreciated!

On 2023/11/01 at 11:52 AM, PsyCLown said:

I stand to be corrected, although I do not think you'd be able to run the 3 inverters in parallel and I don't think you'd be able to combine the AC outputs in your DB board.

Perhaps consider selling the 2x 5KW inverter and buying a 2nd 11KW inverter if you want to have it all running as a single system?

 

Although 22KW of inverter power is quite a lot for the average household. I assume it is more the additional panels which you want to be able to add to the system?

I cannot find the current (amps) limit for the MPPT's, although with 20x 545W panels you're basically maxing out the MPPT wattage limit anyways so one would need to look at an additional inverter for additional PV.

 

if I misunderstood and you have 10x 545W Mecer panels and wanted to split them into 2x strings of 5 panels then you could maybe look at running a string of 10 panels (possibly 5S2P) and then add the JA panels on the other MPPT on the 11KW inverter.

Hi. I am 100% off grid on a farm with many fridges and freezers, cold room, chicken lamps etc, so its needed! I have 20 545 panels to add. Its looking like getting a second 11kw invertyer may be the best option....

56 minutes ago, Deonbayly said:

Hi. I am 100% off grid on a farm with many fridges and freezers, cold room, chicken lamps etc, so its needed! I have 20 545 panels to add. Its looking like getting a second 11kw invertyer may be the best option....

I see, I think a 2nd 11KW inverter will be the simplest solution.

 

You could look at splitting the loads, however that can lead to other issues and may require you to do some monitoring and possibly change the way you do things - this could be a challenge while running a farm.

Sometimes it is best to keep things simple, some things need to just work and should be setup so that you do not need to worry about them.

57 minutes ago, PsyCLown said:

I see, I think a 2nd 11KW inverter will be the simplest solution.

 

You could look at splitting the loads, however that can lead to other issues and may require you to do some monitoring and possibly change the way you do things - this could be a challenge while running a farm.

Sometimes it is best to keep things simple, some things need to just work and should be setup so that you do not need to worry about them.

Exactly my sentiment! There's more than enough other things to go wrong on a farm lol!

Hi @Deonbayly  , you do have an interesting 'problem'  .  The comments from @Coulomb has intrigued me and inspired  me to have a closer look at one of this suggestions to feed one inverters AC output to the input of another inverter.  This is all courtesy of your 11kW machine being grid-tied and therefore allowing ac blending . This may sound wrong as the machine is sold as off-grid , but it is indeed grid-tied limited to zero export but because of this it  has some very interesting ac blending modes of working.

But before we carry on along that road , I need to ask you what  did you plan to solve by the acquisition of the additional inverter, panels and batteries. Is it to increase the system storage capacity in terms of pv and batteries , or do you wish to increase the load output rating ?. In other words , one of my questions is : do you require more than 11kW load rating? 

Edited November 3, 20232 yr by BritishRacingGreen

3 hours ago, BritishRacingGreen said:

Hi @Deonbayly  , you do have an interesting 'problem'  .  The comments from @Coulomb has intrigued me and inspired  me to have a closer look at one of this suggestions to feed one inverters AC output to the input of another inverter.  This is all courtesy of your 11kW machine being grid-tied and therefore allowing ac blending . This may sound wrong as the machine is sold as off-grid , but it is indeed grid-tied limited to zero export but because of this it  has some very interesting ac blending modes of working.

But before we carry on along that road , I need to ask you what  did you plan to solve by the acquisition of the additional inverter, panels and batteries. Is it to increase the system storage capacity in terms of pv and batteries , or do you wish to increase the load output rating ?. In other words , one of my questions is : do you require more than 11kW load rating? 

Hi

I live on a farm 100% off grid. I have 7 fridge freezers, workshop, chicken breeding lamps etc. so i am in the process of doubling my capacity as we get more and more infrastructure. My geysers and boreholes are all on independent solar systems.

I don't require a huge load rating but I do need power for a long time if the weather is poor.

Cheers