question

Hello.
The Inverter has no direct communication to the solar charge controllers and therefore does not recognise how much PV energy is being generated. It can "feel" the rise and fall of the battery bank voltage and/or current (and with this the inverter makes its own % SOC calculation via its internal battery monitor). Hence, one of the better options is to use the Inverter's % state of charge and/or battery voltage for AC Output 2 control via Programmable relay assistant. My comment on the % SOC window, I would suggest you make it wider, for example 5% difference as a minimum, i.e. 95% to kick in, and kick out below 90%. If you make the window too small, with surge loads and intermittent loads, it can kick in and kick out very often in a very short time frame.

Another option you can use and possibly combine with the above programme, is to have a look into the relay switches of the Cerbo GX. Run a separate load triggered via contactors perhaps, but please pay close attention to the relay voltage/current ratings. Some users have used the Relay Function: Generator Start/stop relay to trigger loads.

for information:

my French idea on EasySolar 2 GX (2400W/ 3000VA). If the power consumed is low, you can assume that you have a significant surplus of solar energy. If it is the real case or not, you can switch the ACOUT2 relay ON and wait after the SOC low (75% for exemple) to switch OFF. If solar energy are realy available the battery's SOC will be not degrease. The total power grows up and you must wait a big delay to charge the tank and put OFF the relay. the relay is OFF after 4h (enough for a standard tank) or immediatly if the Victron's inverter is on overload (activate other essentiel load).

For long latencies, it is also necessary to control overload and watch temperature pre-alarm to stop the tank's process quickly for do not run an alarm. The process will be reactivated if all conditions are met.

Only the SOC is used to save battery life if you don't have solar energy enough. (not to activate the process for a long time on one shot, but you can made the calculus to have enough hot water for 25% or X% of SOC). It is essential to separate the function to protect the battery and guarantee enough hot water. It is a compromise you can experiment. In this assistant the behaviour in the case of weak solar, the batterie is used in tampon for charge enouth energy and discharge on the tank. it's like a "solar pump" and the SOC will grows up until the delay of 1200s is terminated. You can try other delais to manage the batterie with this minimal reserved AmpHour.
To stop the process in the night, the relais ACOUT2 is put OFF. It can be OFF by the MPPT solar relay with "day/nigh" detection or by a programmable clock who activates the AUX2 input (solution for my case).
An other advange of this assistant, is that you preserve the life of the AOUT2 relay (1200s min + time of discharge or charge of the battery by solar energy.) (not every 30s in other solutions).
An other advange is that you can install some derivative node to power on other load on ACOUT2. and if a load is not activate, an other load can switch ON. The time allocated for a heating iteration for example can be defined other than per unit of 4h.The allocation of this time can be played experimentally so that all loads relieved are active each in turn.

PIERRE