To the solar owner, in case you would like to monitor your solar generation, grid, and load in realtime (mobile app only), you can consider installing this bidirectional energy monitor (https://expo.tuya.com/product/1105297 , from Shopee or Lazada). NOTE: This is for a single-phase house.

I will recommend an energy monitor with 2 CT, where the 1st CT (current transformer) monitors the TNB input (as Channel A), while the 2nd CT (as Channel B) can either monitor your load or solar wire (subject to the complexity of your wiring). For simplicity, monitor the solar AC input. Channel C is derived from Channel A and Channel B.

For example:-
Channel A: TNB input
Channel B: Solar input
Channel C: Channel A + Channel B = Load/Consumption

NOTE: The above works well if both TNB and solar input meet in the same DB box; otherwise, you will need 2 units of energy monitors, for example, one for the TNB on the ground floor and a second monitor unit on the 2nd or 3rd floor where your solar inverter is connected.

For smart home users using Home Assistant, this energy meter does not give valuable (limited) data for plotting graphical energy flow between grid, solar, and load.

Do a Google search on Smart EV charger and you will find an EV charger where it will monitor your grid export and charge your car accordingly.

I foresee the problem will come after the 10-year contract with TNB ended and the owner decided to install 100 kWH of battery to hold 2 days of sunlight energy and then find out that this energy can only be used in one of the electrical phases (e.g., a certain section of the floor), but the other phases have to draw from TNB.

In summary, underutilize the battery capacity sized for 3 phases, which can only be used by one of the phases.

I wonder if this kind of trick is also practiced by TNB's solar subsidiary.

If I have 13KWac Solar Systems, and able to generate 45.5KWh (13KWac x average of 3.5 Full Day light) per day and size the battery to 1.5 to 2 times of the daily capacity maybe make sense.

The battery will last longer if charge and discharge around 30 to 80% of its rated capacity.

Correct, they keep the admin login to themselves.

If one day you want the Solar System to use isolated WIFI (IOT/Guest wifi) instead of private WIFI, you need to call them to login and change the WIFI connection for you.