So river turbines are not producing power on a commercial scale  anywhere in the world? It's a simple question. And you think they could be, but out of all the supposedly expert planning that's going on for alternative energy no one at ALL has come to the same conclusion?  OK. Got it. 

Similar arguments have been made for nuclear power by fairly famous people: James Lovelock, James Hansen and others. The problem is that it would be a massive undertaking, requiring that new nuclear plant come on line something like every 90 days for the next 30 years.

What you're proposing sounds like a post apocalyptic survival strategy that could be applied on a small scale in a few places after everything else had gone to pieces. As far as  "simple engineering" goes, there are an awful lot of engineers looking at this problem for them not to see something so "simple". Try this.

http://thesolutionsproject.org/infographic/#or