Comment by closewith

Rance and Sihwa Lake are different beasts as they require sea walls or dams, which are immensely more expensive and environmentally damaging, and have extremely limited suitable sites worldwide. They would never be built now (Sihwa is only 15 years old, but the seawall was built in 1994). They are essentially low head hydro installations fed by the tidal range.

The installation in the Pentland Firth is a fundamentally different category as it is installed in open water (albeit in a firth or channel) which is much less environmentally impactful and has 2-4 orders of magnitude more suitable sites globally.