Using Outback FXR with EnPhase Array

vlabs

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Feb 20, 2022
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I have an EnPhase IQ7 array currently operating as a grid tied system with no backup or other complications.
I recently came to own (for free :)) a pair of Outback FXR inverters, and a 48v set Lead Acid batteries.
I'd like to set this new hardware up to enable off-grid operation when the power goes out. I've seen mentions that the FXR is a "hybrid" inverter, but I'm having trouble nailing down whether it will shift the microgrid frequency when the batteries are done charging, and how it would need to be wired. The Outbacks have ACIN and ACOUT, as well as DC battery lugs.

If I connect ACIN and ACOUT to the grid, Can I program it to sink/source power at different times of day? I'm assuming not, as I haven't seen anyone describe that kind of setup.

Can I wire an SPDT relay to switch grid power between the IN/OUT of the outback? It would charge batteries during the day, and discharge at night. I'm comfortable building a system to do that and the Outback seems to be very configurable.

Finally, how can I use this hardware to operate off-grid, if needed? I want the Outback to use it's off-grid inverter functionality to form the microgrid, but I want it to accept power from AC and charge the batteries. It would need to curtail generation by frequency shifting the microgrid. I could use an AC->DC battery charger in parallel to the outback, but then the outback would just power the charger off the batteries in a loop...

I think the first Idea of a grid-tied battery buffer (with a timer+relay to reconfigure) is viable because it's a subset of what the Outback was advertised to do. But as for off-grid AC coupling, I don't really know. Outback recommends a Radian, but that's not what I have. What can be done?
 

timselectric

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You can't connect ac out to the grid. That will get someone killed and is illegal. You can feed the hybrids from your main panel, and then from them to a sub panel. Move critical loads to the new sub panel.
 

vlabs

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The Outback FXR manual clearly describes grid-interactive operation with export to the grid for net-metering, so I'm not sure I understand the issue you're describing. If I were operating during an outage with the FXR in off-grid mode, I would be disconnected from mains service with a transfer switch. The issue is whether the FXR can maintain a micro-grid while sinking power to charge batteries.
 

vlabs

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Thanks for the help! Are you suggesting that the input side of the inverter is capable of maintaining a micro-grid? Or that only the input side is capable of accepting power, and therefore my approach won't work for off-grid operations?
 

timselectric

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You will have to look into the inverters instructions. Different manufacturers do things differently.
Most of the time you would put the hybrid inverter between the grid and micro inverters, and loads.
 

vlabs

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I've done some more reading on this, and I think it's not possible. The charger would need to rapidly ramp current in response to changing loads, which it would not have been designed to do. It is perhaps possible with the IQ8 inverters, which respond directly to changing loads (rather than to the frequency shift of a central inverter). But I have the IQ7. I'll find a more modern "ac coupled" inverter to support off-grid operation, and use the FXR in a camper van project or something.
 

Ampster

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The question appears to be about whether the FXR can AC couple with the micros when the grid is down. The answer may turn on how old the FXR inverters are and whether they are compliant with UL 1741 or its later version UL1741SA. The Enphase IQ7s are most likely UL1741SA compliant. If the FXRs are not UL1741 you might be able to use them with the batteries for battery backup and possibly some load shifting but when the grid is down they would not be able to fire up the micros.
 

vlabs

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My understanding is that they are UL1741(A?) compliant as grid-attached inverters; They will respond to changes in frequency by shutting down/reducing output. This is very common for almost all inverters, it seems. But they don't seem to support generating the frequency shift and absorbing the excess energy for the few seconds where the micros are responding to the frequency change. So they are 1741 _receivers_ (like the IQ7s, but not capable of creating the microgrid themselves.
 

timselectric

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Starting up the micro inverters is easy.
Controlling them, is the hard part.
 

vlabs

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I'm planning to ride my bike at 60rpm and then hop off once it gets going 😑. That's how they did it back in the day, right?
 
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