Generation VS Supply meter readings

[LoxPV]

Hello All

We have 25 panels capable of generating over 8kwh.
I have been monitoring the meters and had expected to see a drop in the mains supply meter reading when generation was high and a corresponding increase when solar generation on a particular day was low.
By and large, this does not seem to be the case.

A recent example:
On a day when 4kwh was generated we had a day mains supply reading of 21 and 5 days later we generated 24kwh and had a supply reading of 14.
The difference in generation is 20 kwh and in supply of 7kwh.

I understand that usage fluctuations would have an effect and that day use extends into dark hours and I have taken this into account, but in the example above, I would expect a much bigger reduction in the supply reading.

It would appear that we might not be effectively using the generated power?

Can anyone give me an explanation of what might be happening?
Thanks

LoxPV