[a smith]

Is it possible to have enough panels so that the mains is not needed at all?

[Stuart]

No. At the moment your just importing electricity. With photovoltaics you can generally stop importing whilst still using your technology during most daylight hours.

Exporting electricity is done when electricity production exceeds demand and then you can either direct it towards heating your hot water tank or feed it to the National Grid and get paid for it or both depending on the size of system installed.