For ages energy has been subtracted from tides and rivers by watermills with a horizontal axis. This was a cheap and reliable source of energy in mills for wood, grain, etc. Nowadays, energy can be transported from the locations with water currents to places were it will be used: grid connected!
Our VAWT turbines have far higher efficiencies too, still making use of tidal currents and flows in rivers. In addition, they even work in remote areas.
" The turbine rotor proved to be self-starting at low currents and the power yield was true to promise."
Roel Notelé, projectingenieur Waterwegen en Zeekanaal NV.