Control the EV charging power with regard to the solar PV output and grid power reading

Correct. In fact, the minimum current required by the standard makes EV chargers less suitable for consuming solar surplus efficiently.

So now, we are focusing on this:Heat the water heater using solar surplus
Utilizing solar surplus by adjusting the boiler’s power in real time.

There is no limitation on the minimum current in this approach, and the adjustment can be made in increments as small as “watts.”