Your solar system app shows production of 20 kWh, but the grid meter records a lower amount of exported energy. Has energy been lost? Usually, the first step is to check whether you are comparing the same quantity: production, the energy you use at the property, and the energy you send to the grid are different quantities.
The discrepancy alone does not prove a fault or an incorrect meter reading. A structured comparison is needed, using the same time period and clearly identifying each reading.
First, identify what each number measures
In the app, you may see “production,” “consumption,” “energy imported from the grid,” or “export.” On a meter display, you may see a cumulative number that has been increasing since it was installed. These numbers are not directly comparable just because they use the same unit, kWh.
- Solar production: the energy generated by the system at the point monitored by that specific reading.
- Energy imported from the grid: the energy entering the property from the grid.
- Energy exported to the grid: the energy leaving the property and going to the grid.
- Total consumption: the energy used by your loads, regardless of the source supplying them.
Also confirm that you are comparing energy in kWh and not instantaneous power in kW. Power describes what is happening at that moment; energy adds up what happened over a period of time.
Self-consumption explains a large difference
In a self-consumption system, some of the production supplies appliances at the property without going to the grid. This energy may be included in the app’s production figure, but it is not recorded as exported energy by the meter that measures exchanges with the grid.
Illustrative example, not an actual customer result: suppose that on one day, a system without a battery generates 20 kWh on the AC side. Of this, 8 kWh is used directly in the home and 12 kWh is exported to the grid. Later, when production is insufficient, the home imports another 5 kWh from the grid.
- The day’s production is 20 kWh.
- The exported energy is 12 kWh and the imported energy is 5 kWh.
- The home’s total consumption is 8 + 5 = 13 kWh.
To keep the example straightforward, we are excluding losses between measurement points and instrument discrepancies. The difference of 8 kWh between production and exported energy is not lost energy: it has been used in the home. Likewise, the 5 kWh of imported energy do not represent your entire consumption.
Compare the same period, with the same start and end times
Before looking at discrepancy percentages, choose a complete period. The app’s “today” reading cannot be compared with the meter’s total reading or with a bill covering different dates.
For a cumulative register, you need two readings from the same register: subtract the initial reading from the final one. For example, export readings of 4.100 and 4.220 kWh correspond to 120 kWh of exported energy over the period in between. The example only shows how to do the calculation.
Ask them to identify which registers measure imported and exported energy on your model. Do not rely on the order in which the display screens change. Note the date, time, and unit, without opening covers or interfering with sealed equipment.
Check the app’s last update time, whether there have been any communication gaps, and whether the selected period is complete. For billing information, also check whether actual or estimated readings are being used. The bill-reading guide helps distinguish the main quantities.
With a battery, ask for the full energy balance
If there is storage, some of the production may charge the battery and be used later. Charging, discharging, changes in stored energy, and conversion losses must also be taken into account. That is why the simple example without a battery does not apply as is.
Do not mechanically subtract exported energy from a “production” reading and call the entire difference direct consumption. With a hybrid inverter, you need to know whether the reading refers to solar production or to a total flow at the device output. The label and calculation depend on the platform and configuration.
Ask your installer to explain the energy balance for your installation and whether charging from the grid is permitted. SMA’s Energy Balance documentation is an example of how different flows are presented and of additional requirements for storage connected on the DC side.
The app needs accurate metering to show consumption
Connecting the inverter to the internet does not mean that all the property’s loads are automatically measured. To view consumption and exchanges with the grid, a compatible monitoring meter may be required, correctly position and configuration.
The photovoltaic monitoring meter and the grid meter may be different devices with different roles. The Fronius Smart Meter documentation, for example, distinguishes between a position at the point of exchange with the grid and a position on the consumption branch. This is not an instruction to change the arrangement yourself.
For general use of the data, see our guide to photovoltaic monitoring.
When a technical inspection is needed
If, after aligning the periods and measurements, the picture is still unclear, gather information rather than changing settings:
- The two meter readings, with dates and register identification.
- An export or screenshots from the app for the same period.
- Information about a battery, a second inverter or recent equipment changes.
- Any alerts and periods without data.
Ask the appropriate professional to inspect the metering arrangement, settings and communication. There is no universal “acceptable percentage” that explains every difference, regardless of the devices and measurement points. If your question concerns meter readings or billing, ask for this to be distinguished from the operational reading in the app.
At Solar Home, we incorporate monitoring into the photovoltaic system design so you know what your equipment is showing. If you are planning a new system, contact us to discuss your needs and the readings you need for everyday use.
