Which inverters can do AC coupled solar on LOADoutput?

I am finding it hard to google this, as you get so many irrelevant hits.

This thread is specifically for AC coupling of Solar on the load output of the inverter
Yes I prefer DC coupling too, and yes I know there are lots of inverters that let you couple AC solar on the Generator port (such as Deye etc). But this topic is not about that.

I only know Victron inverters to be as flexibel as having existing AC solar inverters combined with consuming devices on the load output.
Of course, AC coupled batteries could be applicable. But the Victrons can do it while being inline, performing backup function in case of grid failure.

For most single homes the discussion is not so relevant but for many larger projects with existing AC solar inverters, this flexibility is great.
Are there any other inverters on the market that can do that?

Most tier-1 hardware can. I'm 1000% certain the Magnum MS4024PAE can.

A number of inverters can AC couple to GT PV inverters, hopefully those do Rule-21 frequency-watts and the battery inverter performs frequency shifting.

Sunny Island
Schneider (XW?)
Outback Skybox and Radian
SolArk (recommend not necessarily require connected to "generator" port with relay disconnect. Recommend DC coupled PV > AC coupled PV.)
Midnight Rosie

Not everything works perfectly, so some combinations may be problematic.

I recommend SMA, of course. They invented it. They also make large inverters which I think can as well, but my experience is with Sunny Island.

Thanks I will check them out.

I should have written I am looking at this from a European perspective with EU grid code, meaning that all existing grid-tied PV inverters should indeed be able to work with frequency shifting.

Projects usually consist of peak shaving and/or self consumption, but is great to do that in an inline way that provides backup

Edit: And when searching with "frequency shifting" I immediately get to the right chapters of inverters confirming they can work with it. Why didn't I think of this before to search on that?

do the Sunsynk inverters offer you what youre tying to do?

I am in the UK, and have 2 inverters (with EU certification) and one PV system (installed a few years ago with a guaranteed high rate of return, so i cant add/change etc) it feeds AC to the house and back to the grid.
i also have a Sunsynk hybrid, it is 'set' not to feed into the grid and is connected by a single connection back to the house circuit. A setting on the inverter allows me to harvest the energy produced by the PV - its accessed though the micro generator settings. There is no need for a separate connecting cable (i assume thats what you meant when you mentioned 'not on the generator port'), its done via the internal settings?

i did originally have a Sofar ME3000SP, which also operated in a similar fashion, but it didnt have the option to add a PV system, perhaps one of their other models would?

Swing said:

I should have written I am looking at this from a European perspective with EU grid code, meaning that all existing grid-tied PV inverters should indeed be able to work with frequency shifting.

Projects usually consist of peak shaving and/or self consumption, but is great to do that in an inline way that provides backup

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SMA has four products for European market.

Sunny Island is a 48V low frequency battery inverter, can be stacked in parallel or for 3-phase. Surge 2x rating. It AC couples with GT PV inverters.
I would assume this newer model does peak shaving and time shifting (older model still sold in US does not) but I'm not sure.

The other three use high voltage battery (expensive) and are high frequency designs. Not stackable, only surge about 1.25x so probably need an easy-start for all but the smallest motors.

Sunny Boy Storage AC couples, and requires external relay or grid-backup.
Sunny Boy Smart Energy is DC coupled, overpanel to 200% with AC output plus battery charging. Requires external hardware (future product) for backup.
Sunny Tripower Smart Energy (3-phase) is DC coupled, overpanel to 150%, has built-in AC output for backup without extra hardware.




Quality products, more expensive than the cheap imports but time will tell if those last long enough to actually cost less or not.

Hedges said:

Quality products, more expensive than the cheap imports but time will tell if those last long enough to actually cost less or not.

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Well the great thing about Victron is I know how to work with them. So it is not only about quality but also about support, and not spending a lot of hours that was a bit cheaper to buy.
I will look into SMA a bit more now. I actually would like to go to high voltage but only in freedom of adding my own batteries.

@MisterB1959 Yes it is about not pulling new wires. Especially because distances become bigger and so on.

Yes adding any kind of inverter in an AC coupled manner like you mention with SunSynk and tell it to keep the grid at zero or whatever, will work to some extent.
But it is different from an inline function where you backup the whole thing, including existing PV solar inverters in the load output

I've found SMA support to be quite slow. But manuals are (or for older models were) thorough and that covers most of what I need. I will be installing a few Sunny Boy Smart Energy, may or may not add optional battery later. It is the replacement for Sunny Boy GT PV.
Victron may have more customer-friendly support.

At 48V, there are some BMS for DIY that work with SMA Sunny Island.
There are a few high voltage BMS, but I'm not clear what protocol SMA requires.
REC works well with Sunny Island, I hear. But is quite expensive, especially if used with smaller cells for HV battery.

Loads you want to power is the first thing to consider. What starting surge needed? Sunny Island and some other brands can supply large surge. Most of the HF inverters can't, but some do. I also understand there are issues with AC coupling by HF inverters. Some like SolArk recommend DC coupled PV > AC coupled, so they can respond immediately with internal MPPT, then frequency shift later. If there is load-dump and a few seconds delay for frequency shift, lithium batteries have to absorb that without cells going over-voltage. The hybrids with DC coupling avoid several issues.

Well because of that last part I think it is good to never fully charged the battery.

For now the next project is just a combination of a few small houses with existing PV, doing peakshaving. Nothing special in terms of surges. However, I will eventually run into more business use with more surges, depending on the business.

Not fully charged, but kept balanced to accept the charge. Maybe the recommended battery list models have a solution.
Also for precharge of capacitors before making hard connection. People here have DIY solutions, and REC BMS has one. I would expect BMS of the commercial offerings to slowly turn on FETs to limit surge.

If you want to spend the big bucks, SMA Multi-Cluster is an alternative. Connecting multiple 3-phase Sunny Island.
It looks like this does not support backfeeding grid, with comments about not compatible with European grid as well. But it mentions active anti-islanding.


They used to offer a 70kVA HV battery inverter but I don't see that on their site now. Just multi-MW size, and small ones or home.

Keep in mind, the brand/model of your grid-tied inverters can have significant impact on which hybrid inverter you should pick.

Well the Schneider XW Pro 6848 inverters do in theory work for AC coupling. There are a couple of issues:

1. Getting Schneider XW Pro 6848 configured so that they allow the PV inverters to come on and stay on is rather challenging. I have a solution that is working now, but it required me to design and build a PV shedding system. I actually turned AC coupling OFF and use relays to incrementally turn stings of PV inverters on and off. I will continue experimenting with some of the settings, but information on how all the different setting affect the operation of the Freq / Watt algorithm is hard to come by.
2. Many usage cases are not possible when using AC coupling with Schneider inverters without building some external charging control into the system. Specifically, when either selling or using self consumption (peak shaving) the function will turn off before the "Recharge Threshold" is reached. This means you can't recharge the system again for the next day. Schneider is aware of the issue. They have simply said that it is "Documented Functionality". They do document this limitation in their manual. Maybe they had a reason for not allowing you to program the inverter to sell past the recharge threshold at one time. If they did I can't figure out what it would be, but more modern usage scenarios like grid sell and load shaving don't work because of this limitation.
3. Unless you configure the system to use an External Transfer Switch, you are limited to 60 amps of pass through current. If you are using these inverters as whole home backup system and you have large loads like a dryer, a 5 ton AC, an electric range, and a water heater that is not enough. On my house I have a gas stove, and a 2 ton AC.
4. These systems are modular, and this means you can scale them. However if you are building a large DC coupled system that allows 20,000 watts AC continuous and 15,000 watts of PV, you will need three inverters, the PDP panel, and 3 charge controllers. It will supply up to 40,000 watt surges, but this will be a large wall full of equipment. Compare to two Sol Ark 15Ks or two EG4 18K PV. This system would be maxed out. The AIO solutions would have move room to add additional PV later

The actual hardware for these inverters is very solid. I was testing my system off grid in AC coupled mode with an oven and an electric dryer a few days ago. Both of these items cycle on and off. I had voltages spikes on the DC bus from -200 up to +100 amps. Everything worked perfectly. I had the AC coupling function (frequency / watts) turned off and was using my controller to manage the strings. Under low usage it would cycle between 93 and 95%. Under high usage it would cycle between 89 and 91%. Basically, you don't want to allow high rates of charge as the batteries get more full.

I am going to continue working on fine tuning my settings so that hopefully I can get things to work with the frequency / watts turn on. The problem I am having is that the inverters are turning off and won't come back on when I let the Schneider manage them.

See this post if you are interested in my PV shedding solution:

solar8484 said:

Keep in mind, the brand/model of your grid-tied inverters can have significant impact on which hybrid inverter you should pick.

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You mean there are compatibility issues and out right implementation errors in some of the hardware and software out there? I am shocked.

Seriously though ask on this forum, "Has anyone out there actually gotten this combination of hardware to work together?".

Yes, if you AC couple SMA Sunny Island with Sunny Boy. I use that for grid-backup as do several others (off-grid or grid-backup.)

There are some wattage limits to stay under, different for off-grid vs. on-grid systems.
I think you can build up to 48kW from PV, 24kW from battery, for an off-grid split-phase system. 36kW PV and 18kW battery offgrid 3-phase, or several times larger "multi-cluster".

SMA SI and SB's on 50htz works too.

With a better balance, because they are 230V native, so 6kW SI can take 12kW of SB either on or off grid.
We in the US have same relay with 56A limit, but at only 120V.

Ah reviving this old topic. For now I have chosen to work with Victron.
They can work with any solar inverter, and it really is a mixed bag of inverters.
So no use in vendor locked-in solution.