Calculate power usage

Configuration
3

Two options:
A)
Start with this to calculate time on:

Then create a template sensor where you multiply the result(s) of the above mentioned component with your 0.74kW.
e.g. for yesterday

  - platform: history_stats
    name: Heater ON yesterday
    entity_id: sensor.heater
    state: '1'
    type: time
    end: '{{ now().replace(hour=0).replace(minute=0).replace(second=0) }}'
    duration:
      hours: 24

and the template sensor:

   energy_heater_yesterday:
      value_template: '{{ states.sensor.heater_on_yesterday.state | multiply(0.74) | round(2)}} kWh' 
      friendly_name: 'Heater yesterday kWh'

B)
You mentioned Grafana. I assume you also have InfluxDB.
Do your aggregations using a combination of template sensors (some math inside) and InfluxDB sensors:


However, since you are not reading kWh or kW directly I recommend option A.
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