Two different system in parallel - single phase home

[Ecoeco]

Hi

Long time reader, first time poster here. I’m wondering if anyone can help me with planning my set up.

We have a small 2kw enphase M215 microinverter system that works well and delivers power to our main board and feeds surpluses to the grid. We have had the system for about six years. Our house is wired for single phase, 230v / 50hz (we are in New Zealand).

We are looking at adding another 6 kw of PV generation, taking us to 8kw in total. I’m wondering if we can install a string inverter for the new panels and have that feed into our main board in parallel to the generation from the enphase microinverters.

The options we’ve considered are:
A) update the enphase system with more capacity. We won‘t do this as it is cost prohibitive as we basically need to scrap the M215s, envoy and other enphase gear and start again with a new enphase system.
B) rip out the microinverters and feed them in to a new hybrid inverter - either as a second string on a 8kw inverter or running two hybrid inverters in parallel. This isn’t great as it adds cost to our current setup and I haven’t found an 8kw inverter with ESS backup that is acceptable to our grid lines company yet
C) ideally keep the enphase system as it is since its working fine and then add a new string inverter alongside with both systems providing power to the whole board
D) keep the enphase system, but move about 2kw of load to it via a sub panel and then have the new system power the mainboard and the grid.

Is anyone able to advise if option C is possible? Or if not, if option D is a good idea?

 

[BentleyJ]

I cannot speak specifically about grid-tie inverter specs & certifications for New Zealand. No doubt you have similar anti-islanding rules that require grid-tie PV to either shut down or disconnect when the grid goes down so I believe my experience in the US related to your questions is relevant.

We started with a 3kW DC string system and a Fronius IG Plus grid-tie inverter then a few years later added another 3kW using Enphase M250 inverters. Both feed into the main panel and out to the grid. Never had any problems with incompatibility or failures while operating both systems together.

Presently both systems are now AC coupled with a Schneider XW+ back up inverter and batteries. So far so good after 4 years.

 

[Ecoeco]

I cannot speak specifically about grid-tie inverter specs & certifications for New Zealand. No doubt you have similar anti-islanding rules that require grid-tie PV to either shut down or disconnect when the grid goes down so I believe my experience in the US related to your questions is relevant.

We started with a 3kW DC string system and a Fronius IG Plus grid-tie inverter then a few years later added another 3kW using Enphase M250 inverters. Both feed into the main panel and out to the grid. Never had any problems with incompatibility or failures while operating both systems together.

Presently both systems are now AC coupled with a Schneider XW+ back up inverter and batteries. So far so good after 4 years.

Fantastic - thanks, that‘s exactly what I’m looking to achieve. We have the same shutdown requirements (within 2 seconds of failure or less than a specific voltage coming in from the grid). Our enphase system already does this and we can get a 6kw hybrid inverter which will do the same thing.

I’ll probably go with the Fronius Gen24 inverter for the new string system, which I think will give me the option of DC coupling using BYD batteries, or AC coupling using a Victron inverter.