Purchasing and feed-in compensation of PV current after 20 years
You are wondering if your PV electric current will be accepted by the grid operator after 20 years.
As far as we know, the grid operator is not obliged to take over any current fed in. However, it is unlikely that they would turn it down.
It is more likely that generator operators will have to negotiate the feed-in tariff with the grid operators themselves.
If the tariff offered is too low, the electric current can always be consumed on site.