Major tidal currents are encountered in the Arctic Ocean, the English Channel, Irish Sea, Skagerrak-Kattegat, Hebrides, the gulfs of Mexico and of St Lawrence, the Bay of Fundy, such rivers as the Amazon and Rio de la Plata, the straits of Magellan, Gibraltar, Messina, Sicily, Bosporus. The tidal range is observed as far as 800 km upstream on the Amazon River! In the Far East currents are encountered, a. o. near Taiwan and the Kurile Islands. Northwest and Western Australia have their share. There are many other locations.
Most commonly cited examples are the Pentland Firth, Irish Sea North Channel, Alderney Race, Isle of Wight to Cherbourg, Orkneys to Shetlands. The Florida
Current has been mentioned repeatedly as it is assumed it could provide 25 GW, but the idea of tapping it has caused more than a raised eyebrow among environmentalists.
Where narrow straits occur between landmasses or are adjacent to headlands, large tidal flows develop. For instance in the Iroise Sea, off the Brittany coast, current speeds of 8 knots are not infrequent in the Fromveur passage.
Very high one-way tidal currents exist in the Far East Indies and at the southeast of New Guinea-Papua. Indeed, the westerly movement of the “planetary tidal wave” increases substantially the southwesterly ebb flows in the connecting Pacific – Indian oceans channels, with ebb tides reaching in spots 10 knots. An exploitable 70 TWh/yr would be available in the Sibulu Strait of the Philippines.
Even if huge amounts of energy are available it seems that tidal current power is best adapted for regional, even local sites.