We have already gone a dangerous step into German territory by having super long agreements on price-fixing of feed-in tarriffs for a large enough chunk of electricity to distort the market. Reading the linked article, the embarrassing thing is that Germany still has a large carbon footprint and a much higher carbon intensity than neighbouring France. A negative price for a commodity is not a sign of achievement, it is a sign of a dysfunctional market structure. There is a perverse incentive to keep fossil fuel powered stations going because of the market necessity of the utilities to not go broke keeping a reasonably steady power supply.
If you want to understand my seemingly contrarian views on feed-in tariffs, read the link in its entirity. For a functional market, wholesale cost of a commodity needs to asymptote to the marginal cost of production. Thus solar electricity needs to be set up that - sure, generate your electricity for your own use first, saving you the retail price, but your excess needs to go to the grid for free. If that doesn't pay back the cost of investment quick enough, subsidies should be to reduce the capital investment, not to artificially increase the return for eternity.