An inverter app, smart meter and supplier bill can all be correct while showing different numbers. The first question is what each number measures—not which screen looks most convincing.
Start with four distinct quantities
| Measurement | Likely source | What it answers |
|---|---|---|
| Solar generation | Inverter app or identified generation meter | How much energy was produced at that system’s measurement boundary? |
| Imported electricity | Supplier’s recognized import meter reading | How much grid electricity entered the home? |
| Exported electricity | Official export register or export supplier statement | How much electricity was sent to the grid and recognized for export purposes? |
| Electricity bill | Import supplier statement | What was billed under the actual rates, standing charge and adjustments? |
An in-home display is not necessarily a complete picture of generation and export. An inverter app may measure only part of household demand, especially where batteries, an EV charger or other equipment change the measurement boundary.
Seven checks before challenging a bill
- Write down the billing start and end dates.
- Identify the official import register and whether its readings are actual or estimated.
- Subtract the start cumulative kWh from the end cumulative kWh for each correct register.
- Check the unit rates and standing charges in force during that period, including any multi-rate slots.
- Find the separate export account, if one exists; export credits are not necessarily deducted from the import bill.
- Align the app, meter and supplier periods; delayed data, time zones and daylight-saving changes can introduce differences.
- State the exact unresolved amount or register discrepancy, with timestamps, before contacting the responsible supplier.
A deliberately simplified example
Suppose a no-battery system records 300 kWh generated, 170 kWh exported and 210 kWh imported over exactly the same period, with compatible measurement boundaries. Estimated directly used solar would be 300 − 170 = 130 kWh. Estimated household use would be 130 + 210 = 340 kWh.
That does not mean the electricity bill should show 300 fewer paid units or be zero. Bills still reflect actual imports, rates, standing charges and adjustments. Export income may be settled separately.
This arithmetic does not transfer automatically to homes with batteries, grid charging, different measurement boundaries or missing monitoring data.
The right person to contact
For a billed import register, estimated bill or tariff rate, contact the import supplier. For recognized export readings or payments, contact the export supplier. For a suspected app or sensor configuration issue, provide evidence to the installer or monitoring manufacturer; do not reposition a CT clamp yourself.
Ask for an explanation of the precise register, period and calculation. If export credits are missing, follow the application and MPAN trail.
Keep the bill, safe meter photos, timestamps and correspondence together. The worked fictional bill and monthly sheet in Solar Panels Installed — Now What? show how this reconciliation looks end-to-end.