What's the interest of extending PV by AC Coupling with Micro Inverter rather than MPPT?

Q&A and troubleshooting
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1

Hello

I am thinking to add 2 two more PV panels in another location on my roof (no room for more than 2).

It is unclear of the interest to go the AC Coupling way, vs adding a MPPT. Any comment ?
What micro inverter would work without issue with my MP2GX ?

Thanks for your lights
Matt

PS: my system is made of the following

  • Multiplus 2 GX
  • Smartsolar 250/70 with 3.2kW PV - VE.Direct connected to the MP2GX
  • 15.5kWh 48v LiFePO4 battery
  • All consumers are connected on the AC OUT 1 (nothing on AC IN side, nor on the AC OUT 2)
  • ESS is active, and fully controlled by Node Red
    • MP2GX is connected to the grid (« ON » mode) when appropriate, ie only during the night to charge the battery or if, during a day with low production, the battery reaches a low voltage/SOC point
    • otherwise, it is in « inverter only » mode (disconnected from grid).
2

Directly powering AC loads without DC-DC conversion (MPPTs) and then to AC (inverter). You could argue that using the micros would be slightly more efficient but with just two panels it’s probably not worth the bother. Another reason would be the extra AC inverter capacity you would get when the sun is out. Again, for two panels it’s probably not worth it unless you just want experience AC-coupling solar with a Victron system.

I hope this helps.

3

Hi

This is what I was thinking by feeling, thanks for confirming.
It’s a matter of bit of efficiency to power directly AC, which is what I would prefer for those 2 panels… if this does not lead to absurd expensive setup vs MPPT use.

I am having a very hard time to clearly find micro inverters able to be controlled with frequency shift by the MP2, since it seems to be a recommended thing to avoid situations when being disconnected from grid (inverter only in my case) & battery is full (if no control, I understood the MP2 will shutdown to protect itself, which is definitely not what I would like).

I saw many times the Hoymiles HM range being named, but the most common HMS does not seem to have the feature - and nothing else than Hoymiles found for now…
Is there any list around with suitable Micro inverters ?

Matt

4

I use Hoymiles HMS micros AC-coupled to the output of Victron systems. We have several installations with that configuration and it works just fine. You will need either ESS or the PV Inverter assistant installed on the Multi along with an energy meter such as the Victron VM-3P75CT configured as a PV inverter so you can keep track of the micros. Works a treat!

5

Interesting :face_with_monocle:

I have ESS active but have “inverter only” mode in place most of the time (connected back to grid only when and if necessary (node red controled)).

Is your MP2 connected to grid ?
If not, does that mean your Hoymiles HMS have their production frequency-shift controlled by the MP2 ? (to avoid problems when battery is full) - or maybe your AC-coupled production is sized to fit with the base load consumption of the loads connected behind (ie: 100% self consumption, whatever happens))

Thanks

6

Your PV inverters need to support frequency shifting or be a natively supported device, else the system will have issues trying to coordinate usage, in which case sticking to DC is just simpler. If you are new to this, rather stick to best practice or tried and tested gear, whether that be AC coupled or not.

7

Being new to something does not prevent the willingness to understand, right :smiling_face:?
Which is now done thanks to your feedback and the one previously got. I’m embedded systems and electronics engineer, and very curious, so my brain is well « equipped » to welcome the related informations .

I understood that the frequency shifting (FS) is the way for the MP2, when off grid (or without grid injecton at all), to limit/stop AC-coupled production in case it is above the capacity of consumption (loads and/or battery).

From now, I’m trying to identify which are the suitable/known as working micro inverters, as this FS control feature/capability is not listed on the datasheets :slight_smile:
Hoymiles HM series is known as having the FS-control capability… and I did not find any other reference from my searches.

Feedback from Ed on HMS series is of interest, however as there are many reasons/setup leading to potentially have a non FS-control enabled micro inverter to work anyway without any trouble, I’m digging more on this case to understand better.

8

I live in the United States, where Victron doesn’t provide grid codes and ESS is not supposed to be used because Victron hasn’t provided equipment and software to support grid feed-in here. I’ve spoken with Victron a number of times about this and I’ve been assured a product is coming.

Most of our business is off-grid, but not all. With respect to Hoymiles micros, they were installed on the AC output of the Victron Multis/Quattros and they have no problem controlling the HMS micros via frequency shifting. I have NOT tried this using ESS but it should work just the same.

For practical purposes, stick with MPPT solar. If you want to learn and experiment, then give it a go. :slight_smile:

1 Like
9

Thanks, definitely good to know HMS are frequency shift control enabled :smiling_face: far easier to find on the market than the HM series.

In my case ESS is active, but not much of a thing since I totally control my MP2 behavior using node red , so yes, having ESS on my unit is not expected to influence, however frequency shifting must be enabled.

Thanks again all for the feedback !