Tidal

[[image:renewable-energy-tidal-2.gif]][[image:power_up_tidal_1.gif]]
== Tidal energy devices exploit the natural rise and fall of coastal tidal waters caused principally by the interaction of the gravitational fields of the Sun and Moon. The tide moves a huge amount of water twice each day. Additional monthly and annual lunar cycles vary the strength of these currents, and narrow and shallow constrictions produce the fastest and most powerful movements of current. Different coastlines experiences different fluctuations in tides, with some estuaries accentuating the effect creating tidal ranges of up to 11 metres. ==

== Like many other alternative energies, tidal energy is not really anything new. Tide mills were in use on the coasts of Spain, France and the UK before 1100 AD and in tidal estuaries around 1800 AD (the Schelde River in Belgium). The difference between the tide mill and today's tidal power plant is the size of the unit and the amount of energy generated. ==

== There are basically two methodologies for creating tidal power: == == · by building semi-permeable barrages across estuaries with a high tidal range to dam the water - barrages allow tidal waters to fill an estuary via sluices and to empty through turbines == == · by harnessing offshore tidal streams - tidal streams can be harnessed using offshore underwater devices similar to wind turbines. == == Dams are based on using a barrage at a bay or estuary with a large tidal range. Power is generated primarily at ebb tides as the barrage creates a significant head of water, much like a hydroelectric dam, only smaller. The ebb and flow of the tides can be used to turn a turbine, or it can be used to push air through a pipe, which then turns a turbine. Large barrage facilities can have large lock gates, like the ones used on canals to allow ship s to pass. ==

== Barrage technology is very well established at La Rance, France where a 240 MW plant has operated since 1966. Tidal dams have a serious drawback. Estuaries are amongst the world's most productive and sensitive ecosystems, and the flooding by these barrages causes a great disruption to their natural processes. For this reason this type of tidal energy capture is not considered sustainable. ==

== Harnessing offshore tidal streams has the advantage of being much cheaper to build, and does not have the environmental problems that a tidal barrage would bring. The range of suitable sites is far greater also. ==

== · barrage systems are costly to build, and affect a very wide area - the environment is changed for many kilometres both up- and down-stream == == · the tide needs to actually be moving, therefore they only provide power for approximately 10 hours each day == == · reduced flushing, winter icing and erosion considerably change the ecosystem == == · is only available in a small number of regions - it requires a basin or gulf that has a mean tidal amplitude of 7 metres or above. Also need semi-diurnal tides where there are two high and low tides everyday. ==

== · is a renewable energy source == == · needs no fossil fuel == == · offers free power - once the system is built == == · is a reliable source of electricity == ==<span style="display: block; line-height: 14pt; margin: 0cm 0cm 10pt 165pt; mso-list: l1 level1 lfo3; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto; tab-stops: list 36.0pt; text-align: justify; text-indent: -18pt; text-justify: inter-ideograph;"> · produces no greenhouse gases or other pollutants == ==<span style="display: block; line-height: 14pt; margin: 0cm 0cm 10pt 165pt; mso-list: l1 level1 lfo3; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto; tab-stops: list 36.0pt; text-align: justify; text-indent: -18pt; text-justify: inter-ideograph;"> · is a predictable system == ==<span style="display: block; line-height: 14pt; margin: 0cm 0cm 10pt 165pt; mso-list: l1 level1 lfo3; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto; tab-stops: list 36.0pt; text-align: justify; text-indent: -18pt; text-justify: inter-ideograph;"> · offshore tidal stream turbines and vertical-axis turbines are not very expensive to build and do not have a large environmental impact == ==<span style="display: block; line-height: 14pt; margin: 0cm 0cm 10pt 165pt; mso-list: l1 level1 lfo3; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto; tab-stops: list 36.0pt; text-align: justify; text-indent: -18pt; text-justify: inter-ideograph;"> · may protect a large stretch of coastline against damage from high storm tides == ==<span style="display: block; line-height: 14pt; margin: 0cm 0cm 10pt 165pt; mso-list: l1 level1 lfo3; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto; tab-stops: list 36.0pt; text-align: justify; text-indent: -18pt; text-justify: inter-ideograph;"> · can provide readymade road bridges == ==<span style="display: block; line-height: 14pt; margin: 0cm 0cm 10pt 165pt; mso-list: l1 level1 lfo3; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto; tab-stops: list 36.0pt; text-align: justify; text-indent: -18pt; text-justify: inter-ideograph;"> · the economic life of a tidal power plant is expected long - 75-100years, compared to 35 years for a conventional fossil fuel generating plant. ==

More advantages
==<span style="background: white; display: block; line-height: 14.25pt; margin: 0cm 3.75pt 0pt 36pt; mso-add-space: auto; mso-list: l1 level1 lfo3; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto; tab-stops: list 36.0pt; text-align: justify; text-indent: -18pt; text-justify: inter-ideograph;"> · With water density 832 times that of air, moving water in rivers, tides and ocean currents is the largest source of renewable energy on the planet. For example, an 8 knot tidal current has more energy than a 380km per hour wind. ==

==<span style="background: white; display: block; line-height: 14.25pt; margin: 0cm 3.75pt 0pt 36pt; mso-add-space: auto; mso-list: l1 level1 lfo3; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto; tab-stops: list 36.0pt; text-align: justify; text-indent: -18pt; text-justify: inter-ideograph;"> · Along with the rapid development of wind energy systems, the potential of hydro-kinetic energy is receiving more and more attention. The distinct advantages of hydro-kinetic energy includes the greater predictability of water currents, little if any impact on the visual amenity with turbines placed underwater, and a lower cost of energy production. ==

==<span style="background: white; display: block; line-height: 14.25pt; margin: 0cm 3.75pt 0pt 36pt; mso-add-space: auto; mso-list: l1 level1 lfo3; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto; tab-stops: list 36.0pt; text-align: justify; text-indent: -18pt; text-justify: inter-ideograph;"> · While water energy has been harvested since Roman times, and several free flow or open propeller-type turbines have been installed in ocean currents, there has been little development in the core technology for harnessing this huge yet largely neglected source of renewable energy. The Tidal Energy Pty Ltd concept is to maximize the transfer of energy from the moving water stream to the turbine using venturis. This has led to the development of the Davidson-Hill Venturi Turbine (DHV) capable of efficiencies of 60% from a single turbine rotor. ==

==<span style="background: white; display: block; line-height: 14.25pt; margin: 0cm 3.75pt 10pt 36pt; mso-add-space: auto; mso-list: l1 level1 lfo3; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto; tab-stops: list 36.0pt; text-align: justify; text-indent: -18pt; text-justify: inter-ideograph;"> · DHV turbines employ two Patented components to harness hydro-kinetic energy – a pitching blade rotor that produces more torque and an earlier starting moment and a venturi shaped shroud that increases and accelerates the flow of water over the turbine, working in harmony to extract more energy from moving water than any other design. This advance, similar to the development of the jet engine and the breaking of the sound barrier, translates into greater power production from sites previously not commercially viable. ==

==<span style="display: block; line-height: 14pt; margin: 0cm 0cm 10pt; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto; text-align: justify; text-justify: inter-ideograph;"> Tidal energy is currently more expensive to generate than conventional energy or that from many other renewable sources ==

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====== ===Marine Current Turbines Ltd (MCT), the installation of its 1.2 MW SeaGen commercial tidal energy system will commence during the week of August 20th in Northern Ireland’s Strangford Lough. SeaGen will be the world’s largest tidal current device and will generate clean and sustainable electricity for approximately 1000 homes.===

===SeaGen consists of twin axial flow rotors, each of 16m diameter driving a generator via a gearbox much like a hydro-electric turbine or a wind turbine. The twin power units of each system are mounted on wing-like extensions either side of a tubular steel monopile 3m in diameter which is set into a hole drilled into the seabed. SeaGen will generate electricity from the flow in both directions.===

===The basic requirements for cost-effective power generation from tidal streams using MCT's technology are a mean spring peak velocity exceeding about 2.25 to 2.5m/s (4.5 to 5 knots) with a depth of water of 20 to 30m - the red spots on the map (left) show some of the locations meeting these criteria around the UK and northern France.===