Tidal stream power

Tidal-current (or stream) power is derived from water turbines submerged in the wide expanse of a tidal flow or current there is no constructed barrier. Such a turbine is, therefore, the water-equivalent of a wind turbine. As yet, there are no commercial tidal-current power plants. 

A more benign approach is to extract energy from the tidal flows that occur between headlands and islands or in and out of estuaries. The power available in these tidal streams varies with the cube of the current velocity and while sea currents are typically around 3 m/sec, much lower than the minimum velocities required for wind turbines ( 7m/sec), the density of seawater is such that the output of tidal stream devices is much higher than equivalently sized wind generators. The energy flows are significant with aroimd 7.5 GW of accessible resource in Scotland alone. ... 

An estimate of the dissipation of energy by friction in all of LIS can be made if it is assumed that the only difference in the tidal friction between the eastern and western parts of the Sound is that due to the increased speed of the tidal stream. The power used in work against friction... 

In the next 20 years, hydrokinetic power drawn from the earth s oceans and rivers could account for more than 10% of the world s global electricity market (Wood, 2010). The renewable energy resources from ocean wave, tidal stream, ocean and river current and ocean thermal resources are expected to be the major growth area over the next decade (Marsh, 2009). 

The kinetic energy of a flowing tidal stream per unit time obeys the same power law as that for the wind turbine and is given at any instant in the tidal cycle as equation [19.2] ... 

The cubic relationship between velocity and power is the same as that underlying the power curves of wind turbines, and likewise there are practical limits to the amount of power that can be extracted from tidal streams. Some of these limits relate to the design of the tidal stream devices and others to the characteristics of the resource. 

Wood, K. (2010), Composites-enabled tidal stream energy projects lead the way as new forms of hydrokinetic power generation move towards commercialization , Composites Technology, Composites World, 30 September 2010. 

One of the first Pulse Stream generators was the 100 kW test rig situated in the Humber estuary, which currently feeds power into a chemicals company on the banks of the river. The shells of the blades of one of these Pulse Stream 100 tidal generators were manufactured in glass fibre/epoxy polymer composites the spar was fabricated in carbon fibre/epoxy polymer composites. The spar, which is thick compared with the shell, was manufactured by the infusion technique, but for subsequent generators the prepreg technique will be used to make the spars. Figure 10.8 shows the Pulse Stream 100 tidal generator. 

Power from Currents. Besides the proposed giant rotors in the Gulf Stream, which would be an open-ocean device, a number of projects have been designed for obtaining power from tidal currents in estuaries and other constricted passives using... 

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