Catch an electricity cost fault before the bill

A daily kWh total can be technically correct while a stuck appliance or wrong tariff selector quietly adds cost. Compare current base load with its normal context, calculate cost from your own bill rates, and alarm separately when the accounting path stops making sense.

The fault this project detects

This project detects persistent out-of-hours base load, stale or decreasing source energy and a tariff selector that disagrees with the configured schedule. It builds an indicative daily cost from your own rates without pretending to reproduce every retailer adjustment.

The example assumes a whole-site power sensor in watts, a cumulative import-energy sensor in kWh, a two-tariff plan and a Schedule helper for the actual peak period. Demand charges, controlled load, solar export, shoulder rates and billing adjustments need their own reviewed model.

The evidence model

A useful alarm does not promote one noisy reading straight to an emergency. It combines measurements that fail in different ways:

1. Value: daily kWh and calculated AUD show the accumulating consequence.
2. Direction: a rising out-of-hours power baseline reveals leakage before the billing total is large.
3. Agreement: power, cumulative energy and tariff buckets should move consistently.
4. Context and time: the tariff and occupancy or operating schedule define what consumption is expected, while persistence rejects kettle and compressor starts.

The monitor keeps physical consumption and tariff bookkeeping as separate diagnoses. A wrong tariff selector should not be reported as a failed appliance, and a genuine base-load rise should not wait for the next bill.

Freshness is separate evidence

An entity can keep a plausible old value without becoming unavailable. Inspect last_changed on a source that should genuinely change, and work out your own longest healthy interval between meaningful state changes by scrolling back through that entity's History over a normal week and timing the longest gap between real updates. If the measured process can legitimately stay flat, add a changing source heartbeat or timestamp; do not treat an unchanged temperature, level or power value as proof that the transport is alive.

Rate maths: never copy a gradient

The Trend integration expresses min_gradient in units per second. The arithmetic example from the project brief is 4 °C/hour ÷ 3600 = 0.00111 °C/s. That is an example conversion, not a threshold for this equipment. Calculate the rate from your own timestamped readings: pick two points from that entity's History, subtract the earlier value from the later one for your measured change, divide by the number of seconds between their timestamps for the elapsed seconds, and that division gives you the site-specific gradient. A Derivative helper can instead display a friendlier per-hour unit when configured that way.

Collect this data before choosing a threshold

Use the meter and rates printed on your own current bill. Record several normal weekdays, weekends and hot-weather days before declaring an abnormal base load.

The experiment that makes this article defensible

1. Reconcile the cumulative Home Assistant energy change with the physical or retailer meter over a documented period.
2. Record quiet-period mean power across several normal days, including fridge, freezer and hot-water cycles.
3. Observe every tariff transition for at least one complete plan cycle and confirm the correct Utility Meter bucket increments.
4. Switch one safe plug-in test load on and off to confirm direction and timing; do not alter switchboard wiring or deliberately create a high load.

Keep your own record as you go: timestamped readings, your Home Assistant version, the exact entity IDs you used, and one or two History or dashboard screenshots. Do not stage an unsafe electrical, refrigeration, pressure, battery or water fault merely to make a graph.

Create the helpers

Use Settings → Devices & services → Helpers. Create the named Number or Toggle helpers before loading the templates. Where this guide uses a Derivative, Statistics, History Stats, Integral, Schedule or Utility Meter helper, the current Home Assistant interface can create it; the source links below describe the current options.

Current Home Assistant YAML

Merge top-level keys with your existing configuration instead of duplicating them. Replace the example entity IDs consistently. If you keep automations in automations.yaml, paste only the automation list items there, without a top-level automation: wrapper.

Split cumulative import into daily tariff buckets

This is for a genuine two-tariff plan only. Confirm that sensor.grid_import_energy is a suitable cumulative kWh source. Merge the top-level key if Utility Meter configuration already exists.

utility_meter:
  grid_energy_daily:
    source: sensor.grid_import_energy
    cycle: daily
    tariffs:
      - peak
      - off_peak

automation:
  - id: select_daily_electricity_tariff
    alias: "Electricity - Select daily tariff"
    mode: restart
    triggers:
      - trigger: state
        entity_id: schedule.electricity_peak_period
    actions:
      - action: select.select_option
        target:
          entity_id: select.grid_energy_daily
        data:
          option: >-
            {{ 'peak' if is_state('schedule.electricity_peak_period', 'on')
               else 'off_peak' }}

Calculate indicative cost and flag a persistent quiet load

The cost excludes anything you have not modelled. Compare it with bills before relying on it, and keep rates in helpers so a contract change does not require editing templates.

template:
  - sensor:
      - name: "Grid electricity daily indicative cost"
        unique_id: grid_electricity_daily_indicative_cost
        default_entity_id: sensor.grid_electricity_daily_indicative_cost
        device_class: monetary
        state_class: total
        unit_of_measurement: "AUD"
        availability: >
          {{ has_value('sensor.grid_energy_daily_peak')
             and has_value('sensor.grid_energy_daily_off_peak') }}
        state: >
          {% set peak = (states('sensor.grid_energy_daily_peak') | float)
             * (states('input_number.electricity_peak_rate_aud_per_kwh') | float) %}
          {% set off_peak = (states('sensor.grid_energy_daily_off_peak') | float)
             * (states('input_number.electricity_off_peak_rate_aud_per_kwh') | float) %}
          {{ (peak + off_peak
              + (states('input_number.electricity_daily_supply_charge_aud') | float)) | round(2) }}

  - binary_sensor:
      - name: "Electricity cost warning"
        unique_id: electricity_cost_warning
        default_entity_id: binary_sensor.electricity_cost_warning
        device_class: problem
        delay_on:
          minutes: >
            {{ states('input_number.electricity_cost_hold_minutes') | int(0) }}
        availability: >
          {{ has_value('sensor.grid_power_recent_mean') }}
        state: >
          {{ is_state('binary_sensor.house_quiet_period', 'on')
             and (states('sensor.grid_power_recent_mean') | float)
                 >= (states('input_number.electricity_quiet_load_warning_w') | float) }}
        attributes:
          reason: >-
            Quiet-period mean import is {{ states('sensor.grid_power_recent_mean') }} W;
            today's indicative cost is
            {{ states('sensor.grid_electricity_daily_indicative_cost') }} AUD and tariff is
            {{ states('select.grid_energy_daily') }}.

      - name: "Electricity cost critical"
        unique_id: electricity_cost_critical
        default_entity_id: binary_sensor.electricity_cost_critical
        device_class: problem
        state: >
          {{ is_state('binary_sensor.electricity_cost_warning', 'on')
             and (states('sensor.grid_electricity_daily_indicative_cost') | float(-999999))
                 >= (states('input_number.electricity_cost_critical_aud') | float(999999)) }}

Warning and Critical notification actions

Replace the mobile notification action and media-player entity with your own. Put critical-monitoring-alert.mp3 in /media, test it manually, and leave the monitoring Toggle off until calibration is complete.

automation:
  - id: electricity_cost_warning_push
    alias: "Electricity cost - Warning push"
    mode: single
    triggers:
      - trigger: state
        entity_id: binary_sensor.electricity_cost_warning
        to: "on"
    conditions:
      - condition: state
        entity_id: input_boolean.electricity_cost_monitoring_enabled
        state: "on"
    actions:
      - action: notify.mobile_app_your_phone
        data:
          title: "Electricity cost warning"
          message: >-
            {{ state_attr('binary_sensor.electricity_cost_warning', 'reason')
                or 'The warning condition is active. Check Home Assistant for evidence.' }}

  - id: electricity_cost_critical_repeat
    alias: "Electricity cost - Critical repeat"
    mode: restart
    triggers:
      - trigger: state
        entity_id: binary_sensor.electricity_cost_critical
        to: "on"
    conditions:
      - condition: state
        entity_id: input_boolean.electricity_cost_monitoring_enabled
        state: "on"
    actions:
      - action: notify.mobile_app_your_phone
        data:
          title: "Electricity cost critical"
          message: "The critical condition is active. Check the equipment and evidence now."
      - action: media_player.play_media
        target:
          entity_id: media_player.alert_speaker
        data:
          media_content_id: "media-source://media_source/local/critical-monitoring-alert.mp3"
          media_content_type: "audio/mpeg"
      - repeat:
          while:
            - condition: state
              entity_id: binary_sensor.electricity_cost_critical
              state: "on"
            - condition: template
              value_template: >-
                {{ states('input_number.electricity_cost_critical_repeat_minutes') | int(0) > 0 }}
          sequence:
            - delay:
                minutes: >-
                  {{ states('input_number.electricity_cost_critical_repeat_minutes') | int(0) }}
            - condition: state
              entity_id: binary_sensor.electricity_cost_critical
              state: "on"
            - action: notify.mobile_app_your_phone
              data:
                title: "Electricity cost still critical"
                message: "The critical condition remains active."
            - action: media_player.play_media
              target:
                entity_id: media_player.alert_speaker
              data:
                media_content_id: "media-source://media_source/local/critical-monitoring-alert.mp3"
                media_content_type: "audio/mpeg"

Why the logic works

A Statistics mean filters brief loads, the quiet-period context identifies when the baseline matters, and Utility Meter buckets preserve tariff allocation. The cost consequence raises priority without claiming retailer-grade billing accuracy.

The design is intentionally diagnostic rather than controlling. It reports an impossible or abnormal relationship; it does not bypass equipment protection or decide that a single suspected cause is proven.

Severity tiers without alert fatigue

A weak clue remains visible without interrupting you. A Warning requires persistence or corroboration. Critical is reserved for direct danger or several independent signals. That separation is what stops a useful monitoring system becoming notification wallpaper.

Troubleshooting

Utility Meter totals do not match the bill

Check source units, resets, import versus net energy, tariff timing, GST, fixed charges and retailer adjustments.

Peak and off-peak are reversed

Inspect the Schedule and <code>select.grid_energy_daily</code> around every transition; do not assume off means off-peak on a three-period plan.

Hot water causes expected warnings

Exclude its genuine schedule or build separate baselines that still catch a stuck load.

Solar export creates negative power

Use a true grid-import sensor or separate import and export explicitly; do not feed ambiguous net power into this logic.

Rates changed

Update the helper values from the current contract and preserve the effective date for historical interpretation.

Safety and limits

Do not install current clamps or work inside a switchboard unless appropriately licensed. Use data from compliant meters and integrations. Smart Home Fix is not an electricity retailer, receives zero commissions and does not promise that this indicative cost equals your bill.

If a webhook is added later, treat its webhook_id like a password, keep local_only: true unless a reviewed design requires otherwise, and never use an unauthenticated webhook for locks, garage doors, power isolation or anything destructive.

Official sources

These are the primary documentation pages used for the design. Check them against the Home Assistant or ESPHome version you are actually running.

• Home Assistant Utility Meter
• Home Assistant Statistics
• Home Assistant Template
• Home Assistant Schedule
• Home Assistant Power

Related Smart Home Fix guides

• Set up the Home Assistant Energy dashboard
• Fix unreliable entities before trusting alarms
• Reduce false alarms without hiding real faults

FAQ