You are still incurring a cost if you use the electricity instead of selling it back to the grid

The extent of that heavily depends on where you are. Where I live in NZ, the grid export rates are very low while the import rates are very high.

Our peak import rate is 3x higher than our solar export rate. In other words, we’d need to sell 3 kWh hours of energy to offset the cost of using 1 kWh at peak.

We’re currently in the process of accepting a quote for home batteries. The rates here highly incentivise maximising self-use.

Luxembourg: Purchase price = 2 x sales price, mostly due to grid costs.

And this is with no income tax or VAT on sold electricity.