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That's a good point! I was a bit inaccurate in my text.

This is what the original document says:

When restricted to existing lakes and reservoirs larger than 0.1 km2 in the contiguous United States (excluding the Great Lakes), we estimate the total power available to be up to 325 GW, which is over 69% of the US electrical energy generation rate in 2015

Although this seems to be a form of clean energy there are some major cons in ecological means, especially when rolled out in an extensive way. The problem here is mass adaption in my eyes. Small farms at different places where care is being taken regarding animals, the environment etc. should be calculated according to power generation.

The environment issues are real issues I guess. And maybe a show-stopper. We will see what the future will tell :)