AC coupling: Victron Multiplus + HoyMiles microinverter ?

[Raul a/3]

I had AC coupled off grid with mppt’s as well. In my case, I had a multi 5kva, a fronius TL3kw, one 150/85 Victron mppt, and one 150/35. I hated it. Even being a hybrid AC/ DC coupled, the AC side was tripping if not enough load to keep the fronius going. As it’s on 53hz (Europe grid), the fronius will not connect back, unless a large prolonged load will bring the multi out of the 53hz lock out. A laundry machine will do the trick, and allow the fronius to come back on line, after considerable amount of battery would be cycled. A well pump will not be enough load, as the mppt’s will respond fast and cover that load, but a motor or oven, will always cycle the battery before the fronius will re Connect.
Since then, I modified and upgraded to two 5kva multi in parallel, one 150/85 mppt and one 250/85, all DC coupled, and no more cycles in the battery when there is enough solar.
The only best combo for AC coupled with Victron is Fronius primo, or gen 24. Both work configured for micro grid, and are visible on GX. The modulation with primo is very smooth, unlike the frequency shifting, where the modulation is done in tree abrupt steps.
Off grid since 2014 and learned the hard way few things.
My opinion is, go with high voltage mppt, if the panels are far away, try to avoid AC coupled, unless you have a guaranteed load to swallow all the production, or most of it.

What Andy did there in Australia, works for him, as he’s got loads of consumption and a large amount of DC coupled as well.

 

[RCinFLA]

The wild card risk with AC coupling is if grid drops out losing backfeed power absorption, or you are off grid and you switch off a large load, suddenly leaving significant excess PV power.

It takes up to 2 seconds for freq shifting to begin cutting back PV GT inverter power which is enough time to do damage if PV excess power cannot be immediately pushed to battery, or a secondary load dump, for the period of time required to command PV GT inverter(s) to cutback production.

Frequency shifting works well following relatively slowly changing PV illumination level due to clouds going by but is not quick enough to handle a sudden excess PV power situation when AC loads suddenly drop off.

Grid interactive hybrid inverters are restricted in the rate they shift frequency to no greater than about 0.3 Hz per second.

On many hybrid inverters that allow AC coupling, as soon as you enable AC coupling they will not allow battery to be fully charged to ensure a safety margin for dumping excess PV GT power long enough to accomplish freq shifting control. You never know when grid may collapse and not be able to export excess PV GT power.

This does not prevent the user from having too small of AH batteries that cannot take the maximum back push current. This is a common mistake made by users thinking they don't need large AH batteries because they have so much PV power supplementing.

The hybrid inverter power rating also limits the amount of battery back feed charging power it can convert so maximum PV GT power should not exceed hybrid inverter maximum charging capability.

 

[CRenner]

Hi all,

I'm confused about this 1:1 rule and the size of my system.
I have 18 400w panels. But each has an IQ8+ on them. So max output is 1.21a x 18 = 21.78 x 240v =5227.
So do I use 7200 or 5227 in the calculation?

 

[sunshine_eggo]

The max output of the PV system. If the IQ8+ can only deliver 290W max, then it's 18 * 290W.

 

[CRenner]

Thanks