Unlike wind and wave, tidal power is an inherently predictable source. However the technology is in its infancy and numerous devices are in the prototype stages. Today it is known that a tall tubular tower with three blades attached to it is the typical profile of a wind turbine, but in the earlier stages of the technology’s development there were a wide variety of different systems being tested. Tidal stream power captures energy from the flow of tides, often using underwater plant resembling a small wind turbine although the turbines can be horizontal, vertical, open or ducted. An example is Marine Current Turbines SeaGen 1.2 MW device at Strangford Lough in Northern Ireland, which is the largest tidal stream turbine in the world. To date the only two installed tidal power plants of notable size are the Sihwa Lake Tidal Power Station in Gyeonggi Province, South Korea and the Rance Tidal Power Station in Brittany, France, rated at 254 MW and 240 MW respectively.