Published May 23, 2025

Smart Solar Heating with MiniPLC, ESPHome & Home Assistant

Upgrade your solar heating with MiniPLC, ESPHome & Home Assistant—smart control, real-time data, and energy efficiency in one system.

BeginnerFull instructions provided10 hours207

Smart Solar Heating with MiniPLC, ESPHome & Home Assistant

Things used in this project

Hardware components

HOMEMASTER MiniPLC

pt1000 Sensor

pt100

Adafruit Waterproof DS18B20 Digital temperature sensor

water pump

Software apps and online services

Home Assistant

ESPHome

Story

Overview

In this project, we'll walk through how to connect a solar water heating system to a MiniPLC, using two pumps, multiple temperature sensors (RTD and 1-Wire), and relay control. This setup is ideal for automating and optimizing solar thermal energy utilization in home heating systems.

System Background

The solar water heating system was installed some time ago and originally included the following components:

A solar collector
An indirect heater reservoir
A circulation pump
A controller
One NTC temperature sensor for the reservoir
One PT1000 sensor for the solar collector

The system has since been upgraded:

The old controller was replaced with a MiniPLC
The existing PT1000 sensor for the collector was connected to the new PLC
The circulation pump was connected to the PLC relay outputs
A mixing pump was added and connected to another PLC relay
The reservoir’s NTC sensor was replaced with a PT100 sensor and connected to the PLC

Four 1-Wire temperature sensors were added:

Two for the feed and return lines of the solar collector
Two for the high and low levels of the indirect heating boiler

Firmware and automation logic were developed using **ESPHome**

The MiniPLC was integrated with Home Assistant, enabling real-time monitoring, automation, and control from a centralized dashboard.

Sensor Placement Notes

Accurate temperature measurement is critical for efficient and safe solar water heating system operation. Here's how the sensors are placed and their roles:

PT1000 and PT100 Sensors:

Installed in the factory-designated sensor ports of the solar collector and the reservoir, these sensors ensure reliable and direct temperature measurements. Chosen for their stability and robustness, they are used to control the circulation pump, which is essential to prevent overheating of the solar collector.

1-Wire Sensors (DS18B20):

These sensors are placed under the insulation on the feed and return water pipes, and at the high and low levels of the reservoir. Due to indirect contact with the water, their readings may slightly deviate from actual water temperatures. While not as stable as RTDs, these sensors are suitable for non-critical functions such as monitoring and mixing pump control.

Wiring the Sensors to MiniPLC

Follow the RTD wiring guidelines in the [MiniPLC user manual]. Use analog input terminals for RTD sensors.

PT1000 (2-wire connectiong):

Connect one lead to the RTD/2 terminal 2
Connect the other lead to the RTD/2 terminal 3

PT100 (2-wire):

Similar wiring as PT1000

Connect one lead to the RTD/1 terminal 2
Connect the other lead to the RTD/1 terminal 3

The MiniPLC factory jumper settings are configured for 2-wire RTD connections: RTD/1 terminals are set for PT100, and RTD/2 terminals for PT1000.

Connecting 1-Wire Temperature Sensors (DS18B20):

These sensors require:

3 connections: GND, VCC (3.3V or 5V), and Data. In our case, we use 5V, Data, and GND.
Normally, a 4.7k ohm pull-up resistor between VCC and Data is required, but in this case, it is not needed because the MiniPLC includes a built-in 10k ohm pull-up resistor between VCC and Data is required.

Two sensors were connected to the 1-WIRE/1 bus, and the other two sensors were connected to the 1-WIRE/2 bus on the MiniPLC. Assign unique ROM codes to identify each sensor.

Connecting Pumps to Relays

Use relay outputs of the MiniPLC to control the two pumps:

Mixing Pump Relay Output

The neutral wire goes directly to the pump.
The phase (live) wire from the common circuit breaker connects to the COM terminal of the relay.
The NC (normally closed) contact of the relay connects to the pump's live input.

Circulation Pump Relay Output

Wired the same way as the mixing pump.

The use of the NC (normally closed) contacts ensures that if the PLC fails or loses power, the pumps will automatically start, providing a fail-safe mechanism for continuous operation.

Since the MiniPLC is powered from 230V AC, a single common circuit breaker is used both for powering the PLC and supplying the pumps. This ensures centralized protection and simplifies the installation.

Ensure proper AC isolation and safety procedures when wiring high voltage devices.

PLC Logic (Example Overview)

Program the MiniPLC using a YAML configuration file in ESPHome:

Circulation Pump Logic:

Monitor the PT1000 sensor (solar collector) and compare it with the PT100 sensor (reservoir).
If the temperature difference (delta) is greater than 10°C, start the circulation pump.
If the delta drops below 3°C, stop the circulation pump.

Mixing Pump Logic:

Use the two 1-Wire sensors for the high and low levels in the reservoir.
If the temperature difference between these sensors exceeds 5°C, start the mixing pump.
If the delta drops below 3°C, stop the mixing pump.

All logic and automation were implemented in ESPHome using YAML, allowing for easy updates and integration. This configuration is then exposed and controlled through Home Assistant for seamless monitoring and control.

The full ESPHome YAML configuration used in this project is attached below to help you replicate or adapt the control logic for your own setup

Conclusion

With this configuration, your MiniPLC-based solar water heating system can smartly control pump operations, monitor system temperatures, and maintain efficient heat transfer. This setup reduces energy costs and ensures maximum use of solar energy. Integration with ESPHome and Home Assistant provides a robust platform for intelligent automation and user-friendly control.

ESPHome YAML Configuration for Smart Solar Heating Control

esphome:
  name: miniplc
  friendly_name: "MiniPLC"

esp32:
  board: esp32dev
  framework:
    type: arduino

# Enable logging
logger:


captive_portal:




web_server: 
  port: 80
  version: 3


one_wire:
  - platform: gpio
    pin: GPIO05
    id: hub_1
  - platform: gpio
    pin: GPIO04
    id: hub_2

i2c:
  - id: bus_a
    sda: 32
    scl: 33
    frequency: 400kHz
    timeout: 1s
    scan: true
    



time:
  - platform: pcf8563
    id: pcf8563_time
    address: 0x51
    timezone: "Romania/Bucharest"
  - platform: homeassistant
    # instead try to synchronize via network repeatedly ...
    on_time_sync:
      then:
        # ... and update the RTC when the synchronization was successful
        pcf8563.write_time:

    on_time:
      # Every 5 minutes
      - seconds: /10
        then:
          - if:
              condition:
                lambda: 'return id(collector_temperature).state > id(heater_temperature).state + 10;'
              then:
                - switch.turn_on: relay1
              else:
              - if:
                  condition:
                    lambda: 'return id(collector_temperature).state < id(heater_temperature).state + 5;'
                  then:
                    - switch.turn_off: relay1
      - seconds: /30
        then:
          - if:
              condition:
                lambda: 'return id(heater_up_temperature).state > id(heater_temperature).state + 3;'
              then:
                - switch.turn_on: relay2
              else:
              - if:
                  condition:
                    lambda: 'return id(heater_up_temperature).state < id(heater_temperature).state + 2;'
                  then:
                    - switch.turn_off: relay2

pcf8574:
  - id: 'pcf8574_hub_a'
    address: 0x38
    pcf8575: false
  - id: 'pcf8574_hub_b'
    address: 0x39
    pcf8575: false


spi:
  miso_pin: GPIO12
  mosi_pin: GPIO13
  clk_pin: GPIO14

text_sensor:
  - platform: template
    name: "Current time"
    id: current_time
    lambda: |-
      char str[17];
      time_t currTime = id(pcf8563_time).now().timestamp;
      strftime(str, sizeof(str), "%Y-%m-%d %H:%M", localtime(&currTime));
      return  { str };
    update_interval: 60s


font:
  - file: "gfonts://Roboto"
    id: roboto_small
    size: 8

  - file: "gfonts://Roboto"
    id: roboto_big
    size: 48

  - file: "gfonts://Roboto"
    id: roboto
    size: 14

display:
  - platform: ssd1306_i2c
    model: "SH1106 128x64"
    address: 0x3C 
    rotation: 180
    contrast: 100%
    id: oled_display
#    update_interval: 1s
#    lambda: |-
#       // Print "Mitt Smarta Hus" in top center.
#       it.printf(64, 0, id(font1), TextAlign::TOP_CENTER, "HOMEMASTER");

#       // Print time in HH:MM format
#       it.strftime(0, 60, id(font2), TextAlign::BASELINE_LEFT, "%H:%M", id(pcf8563_time).now());
    pages:
      - id: page1
        lambda: |-
          it.printf(64, 0, id(roboto_small), TextAlign::TOP_CENTER, "HOMEMASTER");
          it.strftime(0, 60, id(roboto_big), TextAlign::BASELINE_LEFT, "%H:%M", id(pcf8563_time).now());
      - id: page2
        lambda: |-
          char str[17];
          time_t currTime = id(pcf8563_time).now().timestamp;
          strftime(str, sizeof(str), "Time: %H:%M", localtime(&currTime)); // Nur Uhrzeit anzeigen
          it.printf(0, 0, id(roboto), "%s", str); // Anzeige der Uhrzeit
          it.printf(0, 20, id(roboto), "Collector: %.1f°C", id(collector_temperature).state); // Display temperature
          it.printf(0, 40, id(roboto), "Heater: %.1f °C", id(heater_temperature).state); // Display humidity
      - id: page3
        lambda: |-
          char str[17];
          time_t currTime = id(pcf8563_time).now().timestamp;
          strftime(str, sizeof(str), "Time: %H:%M", localtime(&currTime)); // Nur Uhrzeit anzeigen
          it.printf(0, 0, id(roboto), "%s", str); // Anzeige der Uhrzeit
          it.printf(0, 20, id(roboto), "Heater up: %.1f°C", id(heater_up_temperature).state); // Display temperature
          it.printf(0, 40, id(roboto), "Heater down: %.1f °C", id(heater_down_temperature).state); // Display humidity
      - id: page4
        lambda: |-
          char str[17];
          time_t currTime = id(pcf8563_time).now().timestamp;
          strftime(str, sizeof(str), "Time: %H:%M", localtime(&currTime)); // Nur Uhrzeit anzeigen
          it.printf(0, 0, id(roboto), "%s", str); // Anzeige der Uhrzeit
          it.printf(0, 20, id(roboto), "Feed water: %.1f°C", id(feed_water_to_collector_T).state); // Display temperature
          it.printf(0, 40, id(roboto), "Return water: %.1f °C", id(return_water_from_collector_T).state); // Display humidity
      - id: page5
        lambda: |-
          char str[17];
          time_t currTime = id(pcf8563_time).now().timestamp;
          strftime(str, sizeof(str), "Time: %H:%M", localtime(&currTime));
          it.printf(0, 0, id(roboto), "%s", str);
          if (id(relay1).state) {
            it.print(0, 20, id(roboto), "Water pump: ON");
          } else {
            it.print(0, 20, id(roboto), "Water pump: OFF");
          }
          if (id(relay2).state) {
            it.print(0, 40, id(roboto), "Mixing pump: ON");
          } else {
            it.print(0, 40, id(roboto), "Mixing pump: OFF");
          }



binary_sensor:
  - platform: gpio
    pin:
      number: GPIO36
    name: "DI #1"
  - platform: gpio
    pin:
      number: GPIO39
    name: "DI #2"
  - platform: gpio
    pin:
      number: GPIO34
    name: "DI #3"
  - platform: gpio
    pin:
      number: GPIO35
    name: "DI #4"
  - platform: gpio
    name: "Button #1"
    pin:
      pcf8574: pcf8574_hub_a
      number: 0
      inverted: true
    filters:
      - delayed_on: 30ms
      - delayed_off: 30ms
    on_press:
    - display.page.show_next: oled_display
  - platform: gpio
    name: "Button #2"
    pin:
      pcf8574: pcf8574_hub_a
      number: 1
      inverted: true
    filters:
      - delayed_on: 30ms
      - delayed_off: 30ms
    on_press:
    - display.page.show_previous: oled_display
  - platform: gpio
    name: "Button #3"
    pin:
      pcf8574: pcf8574_hub_a
      number: 2
      inverted: true
  - platform: gpio
    name: "Button #4"
    pin:
      pcf8574: pcf8574_hub_a
      number: 3
      inverted: true



switch:
 - platform: gpio
   name: "RELAY #1"
   id: relay1
   pin:
      pcf8574: pcf8574_hub_b
      number: 2
      mode:
        output: true
      inverted: false
 - platform: gpio
   name: "RELAY #2"
   id: relay2
   pin:
      pcf8574: pcf8574_hub_b
      number: 1
      mode:
        output: true
      inverted: false
 - platform: gpio
   name: "RELAY #3"
   pin:
      pcf8574: pcf8574_hub_b
      number: 0
      mode:
        output: true
      inverted: true

 - platform: gpio
   name: "RELAY #4"
   pin:
      pcf8574: pcf8574_hub_a
      number: 6
      mode:
        output: true
      inverted: true
 - platform: gpio
   name: "RELAY #5"
   pin:
      pcf8574: pcf8574_hub_a
      number: 5
      mode:
        output: true
      inverted: true
 - platform: gpio
   name: "RELAY #6"
   pin:
      pcf8574: pcf8574_hub_a
      number: 4
      mode:
        output: true
      inverted: true
 - platform: gpio
   name: "LED #2"
   pin:
      pcf8574: pcf8574_hub_b
      number: 3
      mode:
        output: true
      inverted: true
 - platform: gpio
   name: "LED #3"
   pin:
      pcf8574: pcf8574_hub_b
      number: 4
      mode:
        output: true
      inverted: true
 - platform: template
   name: "Switch buzzer"
   optimistic: true
   turn_on_action:
     - output.turn_on: buzzer_output
     - output.ledc.set_frequency:
         id: buzzer_output
         frequency: "2441Hz"
     - output.set_level:
         id: buzzer_output
         level: "75%"
   turn_off_action:
     - output.turn_off: buzzer_output

sensor:
 # WiFi Signal Strength
  - platform: wifi_signal
    name: "MiniPLC Wifi Signal Strength"
    update_interval: 60s
  - platform: uptime
    name: "MiniPLC Uptime"
# Dallas temperature
  - platform: dallas_temp
    one_wire_id: hub_1
    address: 0x973c99e3819c3528
    name: "Heat exchanger down Temp."
    id: heater_down_temperature
    update_interval: 5s
  - platform: dallas_temp
    one_wire_id: hub_1
    address: 0x333c56f649b88328
    name: "Heat exchanger up Temp."
    id: heater_up_temperature
    update_interval: 5s
  - platform: dallas_temp
    one_wire_id: hub_2
    address: 0x0e0000006ac79328
    name: "Feed water from collector"
    id: feed_water_to_collector_T
    update_interval: 5s
  - platform: dallas_temp
    one_wire_id: hub_2
    address: 0x07030d9794011328
    name: "Return water to collector"
    id: return_water_from_collector_T
    update_interval: 5s
    filters:
    - timeout:
        timeout: 10s
        value: 0
 #MAX 31865 RTD 
  - platform: max31865
    name: "MAX 31856 Temperature 1"
    id: collector_temperature
    cs_pin: GPIO1
    reference_resistance: 400 Ω
    rtd_nominal_resistance: 100 Ω
    update_interval: 5s
  - platform: max31865
    name: "MAX 31856 Temperature 2"
    id: heater_temperature
    cs_pin: GPIO3
    reference_resistance: 4000 Ω
    rtd_nominal_resistance: 1000 Ω
    update_interval: 5s
  - platform: ads1115
    multiplexer: 'A0_GND'
    gain: 6.144
    name: "ADC AI4"
    update_interval: 60s
    filters:
      - multiply: 3
  - platform: ads1115
    multiplexer: 'A1_GND'
    gain: 6.144
    name: "ADC AI3"
    update_interval: 60s
    filters:
      - multiply: 3
  - platform: ads1115
    multiplexer: 'A2_GND'
    gain: 6.144
    name: "ADC AI2"
    update_interval: 60s
    filters:
      - multiply: 3
  - platform: ads1115
    multiplexer: 'A3_GND'
    gain: 6.144
    name: "ADC AI1"
    update_interval: 60s
    filters:
      - multiply: 3
  - platform: modbus_controller
    modbus_controller_id: modbus_device
    name: "Modbus Sensor"
    register_type: holding
    address: 0x0001    ## address of the register inside the Modbus slave device
    unit_of_measurement: "C"
    value_type: U_WORD


output:
 - platform: ledc
   pin: GPIO02
   id: buzzer_output  
 - platform: mcp4725
   id: dac_output
status_led:
  pin:
     pcf8574: pcf8574_hub_a
     number: 7
     mode:
       output: true
     inverted: false

Credits

Dmitry

2 projects • 1 follower

Smart Solar Heating with MiniPLC, ESPHome & Home Assistant

Things used in this project

Hardware components

Software apps and online services

Story

Overview

System Background

Sensor Placement Notes

Wiring the Sensors to MiniPLC

Connecting Pumps to Relays

PLC Logic (Example Overview)

Conclusion

Code

ESPHome YAML Configuration for Smart Solar Heating Control

Credits

Dmitry

Comments

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Smart Solar Heating with MiniPLC, ESPHome & Home Assistant

Smart Solar Heating with MiniPLC, ESPHome & Home Assistant

Things used in this project

Hardware components

Software apps and online services

Story

Overview

System Background

Sensor Placement Notes

Wiring the Sensors to MiniPLC

Connecting Pumps to Relays

PLC Logic (Example Overview)

Conclusion

Code

ESPHome YAML Configuration for Smart Solar Heating Control

Credits

Dmitry

Comments

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