FoxESS Community - Owners & Installers Forum

Greetings!

I have new solar/battery system to be installed soon. A FoxESS KH9.9 hybrid inverter paired with a ECS4800-H6 battery and 13.2kW of solar.

My expectations for the system were:
- DC coupling (wasnt a deal breaker, but wanted to know if it was possible)
- Provide whole house backup in the event of a black out (I'm good at monitoring my power usage even without an app )
- Also be able to charge the battery from solar if the blackout lasts longer than usual.

Are these unrealistic expectations of the above hardware?

If by DC coupling, you are referring to how the battery is connected, then AFAIK being a hybrid inverter it can blend AC/DC to charge the battery. DC to DC is preferred as it lowers the losses.

I have a KH7, it has an EPS circuit, and if you read your spec sheets, it will tell you how much power the KH9.9 can supply to the EPS circuit (odds are almost 10kW)

As mine is wired up correctly for EPS circuit, I can confirm that during a recent supply cut to unloop my electric from my neighbour, the PV was charging the battery up.


As you are in Australia, there maybe some regulations that I am not aware of, since you are spending a lot of money, I recommend you put these questions to your installer, if you haven't already done so.

It may be by DC coupling you are referring to PV, the answer to that is yes - any existing panels can be connected to the KH inverter, and it would make more sense doing that than having an older AC coupled system as you will only have one set of losses and full control over export i.e. the system will derate the MPPT's if necessary to suit export limits.

Whole house backup can be more complex than having an EPS 'protected' circuit but very possible, if you do go with a full house changeover you will need to watch the load as heavily inductive loads may cause premature trips and make sure that you have local earthing arrangements in place (in case the incoming grid is totally disconnected).

Whilst running on EPS (effectively in off-grid mode), the PV will still be available as normal.

MaterialBarracuda48 wrote: ↑Fri Feb 06, 2026 9:30 am If by DC coupling, you are referring to how the battery is connected, then AFAIK being a hybrid inverter it can blend AC/DC to charge the battery. DC to DC is preferred as it lowers the losses.

Yep that was what I was referring to. I have another family member who had a Sigenergy system installed, 10kW inverter/40kWh of batteries and 15.6kW solar. The other day to demonstrate they were showing me how they were using the full 10kW of the inverter with the EVAC charger @ 7kW and they switched on a few other loads to bring it up to 10kW and the solar was still charging the battery since the solar was producing 13kW.
I cant afford that setup, but the FoxESS looked like it could do a similar thing, but my googlefu was failing me.

Dave Foster wrote: ↑Fri Feb 06, 2026 11:44 am Whole house backup can be more complex than having an EPS 'protected' circuit but very possible, if you do go with a full house changeover you will need to watch the load as heavily inductive loads may cause premature trips and make sure that you have local earthing arrangements in place (in case the incoming grid is totally disconnected).

Whilst running on EPS (effectively in off-grid mode), the PV will still be available as normal.

I understand. We lose power here a couple times a year, around summer mostly, and its awful with those humid summer nights and no power. Saving the contents of the fridge and running a small split system aircon would make for a happier time.
A whole house backup would be ideal and I'm pretty good at moderating my power usage when needed. I see the KH10 EPS circuit has a max current of 45A, that is more than sufficient for any load I have in my place. The biggest load I have right now is probably the hot water tank. I dont have an EV etc

Now the test will be the installers, hopefully they have the skills to get the system working as I would like. They will be subcontractors Its good to have hopes and dreams because sometimes that is all you get!

Thanks muchly MaterialBarracuda4 & Dave Foster, you have helped me immensely! I'll post back here once I get the gear installed and set up.

Good luck with your install, let's hope they meet your expectations.

After many phone calls, visits by many different electricians the system is installed and working as expected in its current set up. No backup though, I'll have to sort that out later. I'll find a competent electrician to do that work. I didn't trust the installers to do the job properly.

Final hardware was KH9.9 inverter and EQ4800-L6 battery stack with 13.2kW solar, most of the panels are north facing.

Generating 70+kWh a day this time of year, it a crazy amount of energy compared to what my little old 2kW system generated.

The app has all the info I need. I could discharge/charge the battery to and from the grid at a touch of a button. Just wanted to see how easy it was to top up the battery for when there is a run of heavy cloud for days. Happens every few weeks here.

Firmware updates were a breeze, though I always feel nervous doing them. Lingering PTSD from doing PC BIOS updates decades ago

The hardware is great, I couldn't be happier with it.

All of the issues I have encountered were from the staggering amount of ineptitude of the people I had to deal with. From sales, quoting, knowledge of the product (or even their job), workmanship, testing, code of conduct, DNSP requirements. What a clown show. The system wasn't working for nearly a week after final install. They didn't even wire up the HWS!

None of it was obvious that they were going to be like this, it wasn't until there were boots on the ground that cracks started to show. Oh well, lesson learned, glad it hasn't cost me anything extra financially, just time.

Thanks again for you help guys!