Home Assistant: PV surplus, hot water: heating element


Besides the Control my heat pump I can alternatively heat the hot water via a switchable socket and a heating rod. Since my heat pump can only heat the water up to 50°C, the heating rod allows me to generate higher temperatures. If the hot water is heated by an additional 10°C on a day with sufficient sunshine, no hot water heating is required the following day. If the forecast for the expected PV harvest day for the following day falls below a certain value, I have put together an automation to heat the hot water more than usual with the PV electricity generated. Here is the automation in practice:

Legend: Green: PV power generation, Red: consumption; Yellow: heat pump; Dark red: heating rod

Automation in detail

Trigger Description
When meter_power is below -3000 for 6:00

meter_power reflects the data of the smart meter: negative values (-) mean a power surplus

ID: surplus

When heating.hot water is above 60 If the hot water is above 60°C, the corresponding action should turn off:
When meter_power is above 0 no more PV power surplus



'Turn on hot water switch' execute if 'Confirm meter_power is below -3000, Confirm heating.hot water is below 60, and Confirm Pv production tomorrow is below 20' otherwise 'Turn off hot water switch'.


When triggered by surplus.

Confirm heating.hot is above 48 and below 60

Confirm Pv production tomorrow is below 20


Turn on hot water switch


Switch off hot water switch



alias: "Surplus: hot water heater"
description: ""
  - platform: numeric_state
    entity_id: sensor.meter_power
      hours: 0
      minutes: 6
      seconds: 0
    below: -3000
    id: Überschuss
  - platform: numeric_state
    entity_id: sensor.heating_warmwasser
    above: 60
  - platform: numeric_state
    entity_id: sensor.meter_power
    above: 0
condition: []
  - if:
      - condition: trigger
          - Überschuss
      - condition: numeric_state
        entity_id: sensor.heating_warmwasser
        below: 60
        above: 48
      - condition: numeric_state
        entity_id: sensor.pv_production_tomorrow
        below: 20
      - type: turn_on
        device_id: ???
        entity_id: switch.warmwasser_switch
        domain: switch
      - type: turn_off
        device_id: ???
        entity_id: switch.warmwasser_switch
        domain: switch
mode: single

The following page can be used to calculate the amount of energy required for hot water preparation: Online energy calculator: electricity vs. heat pump

To be able to actively intervene in the control of my heating, I use an ESP32 and a 4-channel relay board, see: Control heating: PV surplus with ESP32 & Home Assistant

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