AC Coupling Enphase Microinverters to (old)SW+ 5548s?

Vic

Need to add some PV power to this mature off-grid system.  For convenience,  have considered adding 8-ish PVs to a low slope roof that faces ESE,  and 6 - 8 more PVs facing WNW.   The candidate inverters for these added PVs are Enphase M250s.  This off grid system is one,  as noted in the Signature for this "Post".

There is a 250 foot run of #2 AWG 240 VAC cable running from the Power Room,  to this structure,  and that would be a long run if an additional CC was used with these added PVs.

The main question,  is,  weather the True SineWave AC output waveform from the Stacked Xantrex SW Plus 5548 inverters is clean enough for the Enphase Microinverters to be satisfied that it looks enough like real Grid power, that is  syncs and delivers substantial power to the system.

The sinewave from these inverters have discrete Steps  --  34 steps and 52 steps maximum,  depending on inverter loads and battery voltage.   Each step has a small differentiated blip on each end  ...  one,  positive going,  the other,  negative going,  composed of some high-frequency "noise".

These venerable Xantrex/Trace inverters were produced in volume for several decades,  and Enphase inverters have been produced for more than ten years.  There must be some folks,  here who have tried this combination.  So am looking for any real world experiences.

Finally did get a judgment from Enphase,  stating the AC from the off-grid inverter cannot have any Steps.   But,  bet that all Pure SineWave off-grid inverters DO have steps,  just a matter of degree,  and nature.

May need to buy several Enphase inverters,  and connectors,  and just try it,  but thought would ask here,  first.

Thanks for feedback.   Vic

arby

Found on Google--

<<. Almost all consumer grade inverters that are sold as a "pure sine wave inverter" do not produce a smooth sine wave output at all,[citation needed] just a less choppy output than the square wave >>

https://en.wikipedia.org/wiki/Power_inverter

jonr

I suggest that the issue may not be if it is "clean enough", but if it is sufficiently low impedance and resistant to zero crossing shift.  

Most "pure sine wave" inverters look quite good on an oscilloscope.  And by the time it gets to your socket, utility power isn't a perfect sine wave either.

Vic

Hi arby,  and jonr for the replies.

I HAVE looked at the off-grid inverter waveforms,  and particularly at light loads on the inverter outputs,  the waveform is not divine.   The peak of the sine wave is truncated  --  just chopped off.  This is part of the AC output voltage regulation  approach.

Am not now at any of the off grid locations,  but will try to take a snapshot of the AC waveforms of the OG inverter.   May be able to post an image from the inverter manual ...

And jonr,  believe that Microinverters are simply not able to successfully measure Grid impedance,  as each microinverter has an output power capability of only about 250 Watts (typical PV power available is about 190 or so watts for each microinverter),  and each of the two stacked low frequency inverters that the microinverters are coupled to is rated at 5500 watts continuous.  The battery is relatively stiff,  as well ...

Believe that some/many String Inverters DO attempt to test the impedance of the "Grid",  as they have much more current capability than do individual microinverters.

What is the zero-crossing shift that you referred to?   What is shifting,  and under what conditions?

Thanks!   Vic