TIDAL POWER STATIONS OPERATE BY USING FULL

The primary cause, the lunar tide, is labelled the M2. The height of this tide dwindles to almost zero in a cycle which takes 13.66 days. For example, there is a diurnal tide in the Ross Sea near Antarctica every 24.84 hours. It also follows that some places will have one daily diurnal tide, while other places will have semi-diurnal tides twice a day. This means that if one of the bulges travelling around the Earth is above the equator, then the other bulge is below the equator. For this reason, Cook Strait can experience exceptionally fast tidal flows.Ī third influence occurs because the Moon orbits at an angle to the equator. When it is high tide on one side of Cook Strait it is low tide on the other side. Global surface elevation of the M2 ocean tide (NASA) This computer animation shows the peaks and troughs of the M2 tides sweeping anticlockwise around New Zealand. The gravitation of the Moon and Sun are the most important. However, some of the larger harbours on the west coast of the North Island, in particular the Kaipara, experience significant currents as the tides rise and fall.Īltogether there are sixty-two recognised natural influences on the tides, though only some will be significant at a given location. New Zealand has a relatively small tidal range, usually less than two metres. When the Sun is at right angles to the Moon, the effects are partially cancelled, producing the small tides called neap tides.

TIDAL POWER STATIONS OPERATE BY USING FULL

When the Sun, Earth and Moon are aligned in a straight line (at new and full moon), their tidal effects combine, producing the particularly high and low tides called spring tides. However, the Sun influences the tidal range. Gravitation from the Sun has less influence than the Moon, because it is so much further from Earth. Ī second influence on the tides occurs because of gravitation from the Sun. The effect of the Earth spinning about this centre is that it behaves as a centrifuge, resulting in a second high tide bulge in the ocean most distant from the Moon. This centre is two-thirds out from the centre of the Earth, not at the centre of the Earth. There are actually two high tides, because the Earth and Moon, as a system, both rotate about a common centre of mass. About once a day the Moon rotates around the Earth, attracting as it travels the bulge of water called the high tide that also travels around the Earth. Tides are controlled mainly by the gravitational pull of the Moon. Headlands and constrictions like these focus the currents, giving energy levels reaching 750 W per square metre. Some exception are in and around Cook Strait, where tidal currents can be much stronger, and at the entrance to some harbours, particularly Kaipara Harbour. Tidal currents are usually around two kilometres per hour (one knot). The tide usually ranges between one and two metres. Tidal devices can be weir or dam like structures ( barrages), used to hold the tide back, or turbines anchored within the tidal stream.īy world standards, New Zealand's tides are, for the most part, moderate. Tidal power is generated by capturing some of the energy in the tides as they cycle forth and back, twice each day. Nuclear power proposed as renewable energy.These tidal volumes are 12 times greater than the flows in the largest New Zealand rivers. The harbours produce currents up to 6 knots with tidal flows up to 100,000 cubic metres a second. Other potential locations include the Manukau and Hokianga Harbours, and French Pass. Two resource consents have been granted for pilot projects in Cook Strait itself and in the Tory Channel, and consent is being sought for a project sites at the entrance to the Kaipara. The greater Cook Strait and Kaipara Harbour seem to offer the most promising sites for using underwater turbines. įrom 2008 to 2011, the government Energy Efficiency and Conservation Authority is allocating $2 million each year from a Marine Energy Deployment Fund, set up to encourage the utilisation of this resource. However, the association doesn't list its members. According to their 10 February 2008 newsletter, they have 59 members. The Aotearoa Wave and Tidal Energy Association was established in 2006 to 'promote the uptake of marine energy in New Zealand'. However, not a lot of public information is available about these projects. TVNZ reported in 2007 that over 20 wave and tidal power projects are currently under development. New Zealand has large ocean energy resources but does not yet generate any power from them. Renewable energy sources French Pass has the fastest tidal flows in New Zealand

Tidal power stations operate by using