I believe you can achieve the same thing by shutting the grid tie inverter off using a relay or using the dry contacts on an off grid inverter. Won't be as elegant but it would work, imo
Will it work? Supplementing off grid inverter/battery with on grid PV inverter in one system.
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MajicDiver
Solar Enthusiast
Countless ways to skin a cat if you use your head along the way.
Lol. Are you angry about life?
MajicDiver
Solar Enthusiast
If I were starting from scratch today I would seriously consider the eg4 powerpro and eg4 inverters. But, it appears to me from the traffic on this forum and other places that the EG4 products are still needful of frequent human intervention to keep them running properly- for me the most important thing was seamless integration between inverter/battery/powermeter with an expectation that after system is setup as desired it would be hands off - the system I have has been so in all the configurations I’ve had it in since the beginning between expansions.
apctjb
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@MajicDiver; Thanks for the additional info, very helpful. When and if you figure out a DIY alternative to the ARO batteries please let me know. Would like to do the same but don't have the necessary back gound on the comms side of this.
timselectric
If I can do it, you can do it.
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Can be throttled.
Something external must throttle them.
An off grid inverter without AC coupling capabilities can't do it.
No, many grid tie inverters can self throttle with a zero export option
zanydroid
Solar Wizard
Feels like you’re missing some terminology or theory of operation here.
Frequency shift OR cutting a relay are the main ways to throttle, with the latter potentially being risky due to the potential for stressing the inverter since it’s not tested for so much disconnect cycles.
Not sure what you mean by smart meter.
If the battery inverter is not able to throttle the GTI then the GTI (absent some kind of output limiter, I’m not sure where you would set up a limiter in this picture in a simple way) will keep pushing its nameplate AC power until its anti islanding triggers and it shuts off. There is no UL safety requirement that the GTI must not burn up a off grid inverter, just that it disconnects from grid island within X parameters.
That power has to go somewhere. If there is no well defined sink for the power, then the power is going to get dissipated in random places and that’s probably going to be a fire-adjacent situation
zanydroid
Solar Wizard
Ah I finally read Magic’s profile. That zero export positioning is a good idea, though it does presume a certain response latency on the grid tie inverter/ability for the grid forming inverter to absorb over production/overvoltage within that time.
I would be kind of scared of firmware updates changing behavior. Zero export to grid has much larger safety margin against bugs/behavior changes.
Even with a hybrid that has AC coupling as a supported feature, it’s not like anybody is auditing what layers of firmware and physical protections there are against getting it wrong.
I would be kind of scared of firmware updates changing behavior. Zero export to grid has much larger safety margin against bugs/behavior changes.
Even with a hybrid that has AC coupling as a supported feature, it’s not like anybody is auditing what layers of firmware and physical protections there are against getting it wrong.
The easiest thing may be to DC couple your current array to an mppt charge controller during an outage
timselectric
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timselectric
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See above
MajicDiver
Solar Enthusiast
I agree. I have possession of the current firmware and do not forsee a need to ever upgrade, if i do I will test and either retune or revert if necessary.
zanydroid
Solar Wizard
I don’t think that is the requirement here. Those zero export systems have to average out close enough to zero to satisfy the POCO.
The zero export when hacked up to support this unholy grid forming approach primarily needs to react fast enough to not scorch anything with overvoltage, and secondarily needs to keep anti-islanding disconnections to a minimum (a function of overvoltage). The PWM controller can probably detect a load anomaly (impedance much higher than expected) within a few PWM cycles without even needing the zero export feedback.
timselectric
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The POCO may be fine with an average zero export.
It definitely won't do any damage to the grid.
An off grid inverter being forced to receive power through its output is a different story.
zanydroid
Solar Wizard
Right. I wouldn’t have tried it myself but MajicDiver in this thread has been using strategically placed zero export for a long time to block the GTI from pushing too much into a dumb grid forming inverter and his inverters are still alive.
zanydroid
Solar Wizard
Err it sounds like two months. That’s sort of in the awkward middle of “too short to rule out being lucky” and long enough to recommend. ?
timselectric
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Maybe I misread it. But I thought that he was using two hybrid inverters. One grid-tied and the other off grid?
If both are capable of AC coupling, then there wouldn't be a problem.
zanydroid
Solar Wizard
Good point, AC coupling is in the spec for that inverter. I don’t think his SLD matches how growatt wants them to be tied together (there’s some kind of custom Growatt combiner/transfer switch box), but probably the protective capabilities are a function of the grid forming transformer’s response to the GTI’s behavior, EG safely absorb excess and dampen the anti-islanding detection.
I did not check the model number and assumed they had used some semi random off grid inverter.
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