12. Storing hydro power (Always in motion)

Electric power cannot be stored practically on a large scale.

The Problem

Renewable energy sources, such as run-of-river, wind or solar power stations cannot be adjusted to fluctuating power demands. And both coal and atomic power stations cannot be flexibly run up or switched off to instantly respond to these fluctuations.
So how can power excess, generated for example during the night or during strong winds, be stored for times of peak demand?
A solution was implemented here in Baden, as early as the 1920s and early 1930s...