Hey folks,

I have a Mecer inverter (apparently axpert insides) 5kva.  Model SOL-I-AX-5P.  (Image attached)

On this I have 3 Pylontech US2000 (one is a 2000C)

Also 9 panels of either 330W or 335W.

I started with 6 panels and one US2000.  Over the past year or two I have expanded to what is listed above.

Looking to add a second inverter, to allow 10KW (It is not that we use such immense amounts of power all the time, but, more a case of often having to stop and think about whether or not we can turn on the kettle and coffee-maker right now (maybe while microwave is defrosting something, and pool pump is running).  Kettle will only run for 3 mins, BUT, we cannot run it, since all running together (along with the general household wattage) will pop over the 5KW and will overload.

Installers indicate that they can get me the "partner" inverter and connect it, BUT, they say the second inverter MUST also have panels connected, to work.  They have confirmed that the two inverters will share the battery-bank (via a "bus-bar" setup?).  But, if no panels on the inverter, then the inverters/system may be (my own words) unbalance/unstable.  I have found contradictory statements regularly in their explanations, and therefore I am asking on these forums, as my own knowledge is way too limited.

I have come across posts in powerforum where folks using Axpert inverters were apparently using two in parallel with panels only on one.  Additionally, I think to myself:  what happens at night....no panels are operating at night?

So, the question:  does anyone have experience of, of knowledge of using above-mentioned inverters in parallel with panels only on one?

TLDR

So, another part of why I am trying to find out, is:  the installer seems to be very expensive.  They did my initial install, and prices were comparable to other installers at that time.  But, at present, they are quoting prices that appear to be way out of whack, and I think it is simply because they are very busy, and thus can ask "what they like" in a sense.  They are good installers, and did a great job installing the initial system, but, over the past three years, every time I expanded, it seemed to me that the prices were getting more and more excessive.

Just as an example:  A Pylontech US3000C can be bought for around R18000 at the time of this writing.  Yet, their quote (for ONLY the battery - no install, just the battery) is R24000.  Similar is true for the panels they quoted.  Thus, I am going to purchase a battery myself.  Purchase panels myself (as funds are available), and simply ask them to install, or get quotes from competing installers.

The one massive challenge that I have is the actual inverter.  It appears that no-one whom I have asked, is able to get or supply an inverter that can parallel with this one, and worse:  it seems these inverters are now discontinued (according to my above-mentioned supplier).  They do, however, appear to have a last one in stock.  So, rather than replacing the inverter with an entirely different one, I simply want to attempt to add the extra one so long, hoping to add batteries and panels during the coming year.

I am hoping to thus get only the inverter installed, and later, once panels are purchased, get an installer at a more reasonable cost.  But, as mentioned above, this installer sticks to their guns that I need to get panels and have them installed also.  Since I am now slightly weary of them , I ask the folks here for input 🙂
 

Thanks in advance to any who can assist.

11 hours ago, Riaan Eloff said:

Installers indicate that they can get me the "partner" inverter and connect it,

You do need a good installer to find the exact right model, and who can deal with the frequent firmware issues that arise. Usually, you will need the same, or very similar, firmware running on the two, and that can be a challenge when the inverter is 20 months old, as yours is. Finally, a parallel install is slightly tricky; if you don't do the steps in the right order, there is the chance of blowing them both up.

I resisted a second inverter for a while, but now have two. While one was repairing, I had to run on one for a while, and it was significantly less convenient, as you have noted. It is worse for me though as mine are only rated at 4 kW (but still 5 kVA).

11 hours ago, Riaan Eloff said:

BUT, they say the second inverter MUST also have panels connected, to work.

This is simply not true. I don't know where they are getting that idea from.

Hey Coulomb, thanks for the informative reply.

If I were to purchase the inverter from them, is it possible for me to update the firmware myself, or is that not as simple as I am making it sound?

5 hours ago, Riaan Eloff said:

If I were to purchase the inverter from them, is it possible for me to update the firmware myself, or is that not as simple as I am making it sound?

The actual programming is fairly straightforward. You need a Windows computer and a USB to serial interface. Some interfaces don't work well for this; there are several that are well known and readily available in South Africa. The AEVA page mentions two of them.

The hardest part is deciding which firmware version you need for your particular hardware, and where to download it from. 

In your case, you just need to make sure it's not a 64 V model; see what the highest possible absorb/bulk voltage setting is (it will be 58.4 V or 64.0 V). So then the firmware you need is 72.40 or later, or if it is 64 V, then 72.20 or later. Beware of version number overlaps! For example, there are old PF0.8 firmwares with the number 72.20.

You can get fully patched firmware for these models as well, in either the LPF or non-LFP (called LC) flavours. All available from the link above. The fully patched firmwares fix the dreaded premature float bug, and add some nice features such as KettleKomp™.

In summary: updating the firmware yourself is not trivial, but not very hard either.

If you pay lots of hard money for an installer, it will be his responsibility to make the two inverters work together in parallel. It is mandatory that they run the exactly same firmware version, otherwise there will be an error message. And Coulomb is right, there is no need for both having solar panels. I ran my two Synerjy/Axpert MKS 5K (5kW) for quite a while with panels only on one unit. Reading your product label it appears to be quit equal as mines. Mines run firmware 74.40.

I installed the units myself, I have the advantage to be in that trade. It worked out well and they keep running.

Hey folks,

just a quick thank-you for the responses.  Much appreciated.