This document will demonstrate a method for linearly controlling the power output of the resistive load(such as the heater in the boiler tank) in the home assistant.

If you have both a solar PV system and a resistive load, you can save even more money by using this method. By reducing or shutting off the load power when the system draws energy from the grid and increasing the load power when energy is being exported to the grid, you would manage costs effectively. This strategy ensures that more of the energy generated by the solar system is utilized on-site, reducing the amount exported to the grid (More self-use rate).

For more details ,please refer to  

https://community.home-assistant.io/t/esp32-scr-module-linearly-adjust-the-power-output-of-resistive-loads-such-as-heaters/726575

Video: add the SCR module into the Home assistant https://youtu.be/ywJmEiGIly8
Video: ESPHome API https://youtu.be/g4xueaTHrl4