Solar panel pump with differential in/out temperature sensing for pump control

solar.yaml

input_number:
  ### Solar Pump Hysteresis Offsets ##
  pump_off_offset:
      name: Pump OFF offset
      initial: 0.1
      min: 0
      max: 2
      step: 0.1

  pump_on_offset:
     name: Pump ON offset
     initial: 3
     min: 0
     max: 10
     step: 0.5

sensor:
  ## Water Out Temp ##
  - platform: mqtt
    state_topic: "/solar/exit/temperature"
    name: "Solar Temperature"
    qos: 0
    unit_of_measurement: "C"

  ## Water In Temp ##
  - platform: mqtt
    state_topic: "/solar/Tin/temperature"
    name: "Solar Input Temperature"
    qos: 0
    unit_of_measurement: "C"

  # GPIO 12 for PWM Control
  - platform: mqtt
    state_topic: "/solar/pwm/12"
    name: "Solar Motor Value"
    qos: 0

  - platform: template
    sensors:
        temp_diff:
          friendly_name: Temperature Difference
          value_template: >
            {% if ((states.sensor.solar_temperature.state | float ) - (states.sensor.pool_temperature.state | float))
              < (states.input_number.pump_off_offset.state | float ) %} pump_off
            {% elif ((states.sensor.solar_temperature.state | float ) - (states.sensor.pool_temperature.state | float))
              > (states.input_number.pump_on_offset.state | float ) %} pump_on
            {% else %} pending {% endif %}

switch:
  - platform: mqtt
    name: "Solar Pump"
    state_topic: "/solar/pwm/12"
    command_topic: "/solar/pwm/12"
    payload_on: "1023"
    payload_off: "0"
    qos: 1
    retain: true

Thanks again for the swift reply.
So I set up a packages folder as per Packages in Home Assistant (https://www.home-assistant.io/docs/configuration/packages/). Downloaded your solar.yaml and included packages in my configuration.yaml.
I need to modify my ESPHome DS18B20 temperature sensors to replace your platform: mqtt sensor. However I do not see any of the history graph or status window. Am I missing something. Thanks