As you mentioned, this is possible but often followed by lots of regulatory things. I had a look into it for Germany and the easiest way is to buy an old mill and retrofit new technology for power generation.
On the other hand, older mills are often covered by the protection of historical monuments and can therefore not be altered as you like. This should really be looked into before buying anything as it will be an absolute showstopper with no way around it.
And if you try to do what the guy here did you'll most likely run into water way authorities with requirements for fish ladders and so on.
It's doable but it's not as easy as laying some pipe through your garden.
On the other hand, older mills are often covered by the protection of historical monuments and can therefore not be altered as you like. This should really be looked into before buying anything as it will be an absolute showstopper with no way around it.
And if you try to do what the guy here did you'll most likely run into water way authorities with requirements for fish ladders and so on.
It's doable but it's not as easy as laying some pipe through your garden.