Earlier quoted context omitted.
In the UK you can sell electricity domestically for 20c/kWh so at least here that's the cost if you have PV. If you don't, the cost is higher.
It's not a cost if you self-consume your energy, even if you get paid for what you inject. You are just amortizing differently the cost of the PV installation. But what you get for the energy you sell is not real money, it's just money you MIGHT consume as energy in other periods.
Is the model you're describing (usage credits) in the European market somewhere ?