DC coupled or AC coupled conundrum

[jammin]

I have an existing SolarEdge system with SE6000H inverter and 20 panels with S440 optimisers. I am in NSW, Australia.

The optimisers are important as some panels are partly shaded at different times of the day. Example shown in the attached images where at 10am panel 14 is mostly shaded:

But at 2pm, panel 3 is shaded and panel 14 back to full sun.

It's a small roof almost entirely covered, so better placement was not an option.

(although there is potential for another 6 south-facing panels)

I am looking to get am EQ4800 full stack, and most installers have been recommending AC coupling this system and just leaving the Solaredge system as-is, but I feel this would introduce complexities in dealing with 2 inverters and ecosystems, and especially if looking at VPP programs. I am concerned the Fox system would not be fully aware of house consumption, grid production etc as it all just happens on the same AC bus. Would love anyone to expand on whether this is actually the case with correctly placed CT clamps etc. Ideally I'd not want to look at Solaredge system again, except to look at things like panel level production.

The other option some have suggested would be to DC couple the panels, removing the Solaredge inverter and optimisers in the process. I'm concerned this would reduce the panel output due to the shading issues. I have read that Tigo optimisers could be an option here, and it looks like it would be about $2000 AUD to replace the SE optimisers with Tigo ones and remove Solaredge from the equation completely. I'd be willing to pay this for a more optimised and simple system.

I'm wondering what people here would advise - if I went the Tigo route would I get individual panel production in the Fox ESS interface like I have now?

Are my AC coupling concerns unjustified, and am I just shooting myself in the foot removing reliable well performing gear?

Thanks!

[Dave Foster]

I can’t comment on the VPP stuff myself, there is also a community Facebook group here https://www.facebook.com/groups/foxessownersgroup with a lot of Australian members and you’ll likely get a better response there to that question.

In terms of DC vs AC coupled, if your AC coupled systems can be monitored at a single point i.e. if they combine in a single distribution unit you can clip a second CT to that feed which will be able to measure the absolute power being generated by those panels and your house load / grid statistics will be correct.

If you cannot do that because the AC coupled systems are connected at multiple locations, the Fox system will still work perfectly in that it will see any excess solar on it’s main CT and will use that to charge the batteries. But you are correct in that the system will not be able to provide house load metrics and accurate statistics (when the sun is out).

[jammin]

Thanks for the reply.

Seems there is not much downside to AC coupling. I might do that and enquire about getting another 6 new panels connected to the fox inverters so I have a small capability to charge the battery when there is no AC power. And to increase ability to fill this enormous battery of course!

[WyndStryke]

I believe that it is possible for SolarEdge optimisers to run in 'indop' (independent operation) mode, rather than being tied to the solaredge inverter. I don't know if this is possible once they have already been commissioned, nor do I know the pros & cons of running this way, nor do I know if it is a universal feature on all solaredge optimisers. If it is possible, then you would not need to buy new Tigo optimisers (the solaredge optimisers have a better reputation than tigos, although tigos are popular here, and I have them on my own roof).

The simplest solution would be to AC couple the new battery, or to use solaredge batteries.