4 hours ago, Scorp007 said:

I find it strange that the diagram does not show the essential bit that the string inverter has its own PV connected.? 

You're right!

A non-PV-requiring  use case might be a small inverter/UPS-type device (with it's own incompatible battery), say, powering a handful of critical PC and office equipment. If the power fails, the larger upstream inverter keeps the little one charged and operating at full battery; and when the the upstream inverter's battery runs out and cuts off its load port, then those critical devices can continue for a bit on the smaller inverter.

This makes me wonder if it might be worth pulling out my own old (Must-clone) 12V inverter (complete with it's nasty lead-acids which I've kept floated since decommissioning) and powering just my Wifi and Fridge off it, downstream from the main inverter - a pair of 'super-essentials', so to speak. This way I cycle those lead-acid-batteries as infrequently as possible - only in the rare occasion that the main inverter runs out of battery. The disadvantage is that it adds extra DB wiring requirements, adds extra points of failure; and the considerations I mention in my previous post become pertinent: (that little thing was rated for >2kW charging of those 12V's parallel AGM's - pretty significant!).

 

My Deye inverter connection.

Zero Export to CT is on.

I would like the battery to be charged only when the second installation is generating electricity, the rest of the time it is powered by the battery.

unfortunately, in this setting, the current is drawn from the mains to charge the battery even though Zero Export to CT is on.

please advise.

37 minutes ago, krzysiekfdds said:

Zero Export to CT

This is you feeding power to the grid and has nothing to do with importing from the grid and with this imported power charging the battery...

There is a setting on the inverter that states how much, if any power from the grid can be used to charge the battery...

Of course I give the excess energy to the grid.

First I have set the battery charging, then Home Load.

After selecting the option from the picture the battery charges, but Zero Export to CT is not maintained when the battery is charging.

When the Battery is full the inverter supplies energy from the battery if necessary to maintain Zero Export to CT.

On 2025/03/07 at 10:10 AM, krzysiekfdds said:

After selecting the option from the picture the battery char

On 2025/03/07 at 10:10 AM, krzysiekfdds said:

After selecting the option from the picture the battery charges, but Zero Export to CT is not maintained when the battery is charging.

Your setup is problematic to say the least, I doubt there's a way for the two inverters to communicate and thus do what you want... also the above "...Export to CT is not maintained..." I'd think the exporting is done by the other inverter, not the one with the battery...;

Hello.

The second inverter is an On-Grid type.

When the sun appears, it transfers all the energy produced to the grid. There is no CT in it, it only synchronizes with the power grid and transfers energy from the PV panels.

Zero Export to CT is maintained if the batteries are not charging.

Limited to 5kW

.

27 minutes ago, krzysiekfdds said:

Hello.

The second inverter is an On-Grid type.

When the sun appears, it transfers all the energy produced to the grid. There is no CT in it, it only synchronizes with the power grid and transfers energy from the PV panels.

Zero Export to CT is maintained if the batteries are not charging.

Limited to 5kW

.

As said by @Kalahari Meerkat , your system is a bit problematic. Normally the grid-tied string inverter would be connected to the AUX/Gen port and controlled as a micro-inverter. In this case you're using that port for your generator.

I'd suggest to re-position the connection of your grid-tied inverter to somewhere between the CT coil and your grid meter. That way you could treat it as part of the grid from the point of view of your Deye inverter. The Zero-Export to CT function should then prevent you importing power from your grid-tie inverter to the Deye inverter; it will rather export to the outside grid past the meter.

Together with that, you could set up a Time-of-Use schedule that allows a Grid Charge during the daytime, where "Grid" would then in actual fact be coming from your grid-tie, but not exclusively.

Alternatively, why not transfer your solar panels to the Deye inverter, and just ditch the grid-tie inverter? Mine is gathering dust, it is simply obsolete in this setup.

Edited March 8, 20251 yr by GreenFields

The PV installation is a bit far from the Grid and CT connection. I will connect the old On-grid inverter to the Gen input, I will see if I can achieve Zero Extport to CT then. However I would like to avoid installing a new power cable,