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288  OCEAN ENERGY TECHNOLOGIES



                         MOON
                     QUARTER PHASE





                                     SOLAR TIDE



                                     LUNAR TIDE

                       NEAP TIDES



                        SOLAR TIDE





                                      MOON
                                   FULL OR NEW
                        LUNAR TIDE
                      SPRING TIDES
                      Figure 9.1  The effects of the moon and sun on
                      ocean tides.



                     sun are at right angles to each other, lower tidal differences are experienced, which
                     results in the neap tides (Fig. 9.1).



                     Tidal Power Generation


                     The generation of electricity from tides is similar to hydroelectric generation, with the
                     exception that water flows in and out of the turbines in both directions. Therefore, gen-
                     erators are designed to produce power when the rotor is turned in either direction.
                       A tidal power station, known as an ebb-generating system, involves the construction
                     of a dam, known as a barrage, across an estuary. A number of sluice gates on the bar-
                     rage allow the tidal basin to fill with the incoming high tides and to exit through the
                     turbine system on the outgoing tide, referred to as the ebb tide. As mentioned earli-
                     er, special generators used to produce electricity on both incoming and ebb tides are
                     also possible.
                       Tidal power is a technology that makes use of captured energy contained in moving
                     water mass owing to tides for conversion into electricity.  Types of tidal energies
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