Why does Inverter Output differ from generation meter reading?

A common question about solar panels is why the reading that the generation meter shows is different to the reading shown by the solar inverter. The difference between the two readings can work either way, sometimes the inverter reads a higher generation figure, sometimes the generation meter can give the higher reading from the solar panels.

The reason is that the generation meter gives the correct number as it is calibrated and produced to a specific tolerance to meet the requirements of the MCS scheme in the UK and electricity companies. The value shown by the solar inverter is only an estimate and can be a few percent different to the solar generation meter.

As an example our generation meter yesterday passed the 4MWh milestone for generated solar electricity but our inverter is still only at 3952 kWh. The difference between the two readings is around 1.5% with the generation meter giving the higher reading.


Why does Inverter Output differ from generation meter reading?
Inverter reads 3958kWh



Why does Inverter Output differ from generation meter reading?
Generation meter reads 4006kWh