Oh it’s absolutely possible to do it legally in Germany: Land, natural resources and means of productions can be socialised without even having to show that it’s for the common good, and compensation wouldn’t be what RWE is hoping for as the amount will not only take their interests into account but also that of the public. Article 15 GG.
But that article has never been used and I indeed would very much prefer if the first time it’s used it’s expropriating landlords in Berlin.
Another interesting approach would be to take Article 14 (2) seriously and demand that RWE buys carbon credits for every single ton of coal they pull out of there. Sure it’s their coal noone is disputing that but using it comes with an obligation to not hurt, if not serve, the common good.