@Steve777 First, make sure you are updated to the latest firmware #6 as it has fixed some on_grid with grid feed-in use cases.
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Based on my own experience, here are my interpretations of the operation of the inverter.
1. Max feed-in is the max power selling back to the utility but i didn't get a chance to test this because when my inverter was installed in october, I need the max power of my AC coupled solar + DC string on the inverter. The One does measure grid-in properly when comparing to the Enphase consumption CT meter as well. The only question is how graceful the power control is. My previously outback skybox did this perfectly. It throttled its own DC PV power to meet max sell-back.
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2. If you allow Discharge end SOC (on-grid), the inverter will use battery and try to zero out all the usage at the point of the CT. If you set 300W (default), it is where the algorithm tries to maintain. I'm guessing this is the inverter's way to have some buffer against accidentally feed-in by always trying to consume some power versus trying to really cancel out all power consumed. Weird that 30W is the lowest it can go and not true 0W if I have a NEM agreement with the utility company.
3. I think you are right, this setting should zero out AC side house loads plus the Loads Out if you have set up the CT and associated setting of the CT properly.
4. I am guessing this is the re-bulk setting?
5. Something funny going on with the reporting of the MPPTs. I pull the data directly from the inverter and I can't seem to get individual MPPTx power but there is a "PV Total Input Power" and it's quite noisy when I would expect this to be 0W.
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6. Same issue observed. I think there are inverter and app updates to improve the data coming post new years.
7. Unfortunately not. Push midnite to document and TEST more because on-grid use cases are not fully documented, let alone tested. The replies I get are along the lines of "there are over 500 installs of the MN15 inverter...", implying people aren't encountering the issues I am reporting...
Good luck and please post your findings in this thread as well!