New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

has large ocean energy resources but does not yet generate any power from them. TVNZ reported in 2007 that over 20

wave In physics, mathematics, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium (re ...

and

tidal power Tidal power or tidal energy is harnessed by converting energy from tides into useful forms of power, mainly electricity using various methods. Although not yet widely used, tidal energy has the potential for future electricity generation. Ti ...

projects are currently under development. However, not a lot of public information is available about these projects. The

Aotearoa Wave and Tidal Energy Association The Aotearoa Wave and Tidal Energy Association (AWATEA) is a New Zealand organisation established in 2006 to promote renewable energy from marine sources. This includes energy from Tidal power, tides, wave power, waves and Marine current power, oc ...

was established in 2006 to "promote the uptake of marine energy in New Zealand". According to their 10 February 2008 newsletter, they have 59 members. However, the association doesn't list its members. From 2008 to 2011, the government

Energy Efficiency and Conservation Authority Energy Efficiency and Conservation Authority (EECA) is a New Zealand government/Crown agency responsible for promoting energy efficiency and conservation. The EECA was set up by the Fourth National Government of New Zealand in 1992 to encourage, ...

is allocating $2 million each year from a Marine Energy Deployment Fund, set up to encourage the utilisation of this resource. The greater

Cook Strait Cook Strait ( mi, Te Moana-o-Raukawa) separates the North and South Islands of New Zealand. The strait connects the Tasman Sea on the northwest with the South Pacific Ocean on the southeast. It is wide at its narrowest point,McLintock, A ...

and

Kaipara Harbour Kaipara Harbour is a large enclosed harbour estuary complex on the north western side of the North Island of New Zealand. The northern part of the harbour is administered by the Kaipara District and the southern part is administered by the Auckla ...

seem to offer the most promising sites for using underwater turbines. Two resource consents have been granted for pilot projects in Cook Strait itself and in the

Tory Channel Tory Channel / Kura Te Au is one of the drowned valleys that form the Marlborough Sounds in New Zealand. Inter-island ferries normally use it as the principal channel between Cook Strait and the Marlborough Sounds. Tory Channel / Kura Te Au lies ...

, and consent is being sought for a project sites at the entrance to the Kaipara. Other potential locations include the

Manukau Manukau (), or Manukau Central, is a suburb of South Auckland, New Zealand, centred on the Manukau City Centre business district. It is located 23 kilometres south of the Auckland Central Business District, west of the Southern Motorway, so ...

and

Hokianga Harbour The Hokianga is an area surrounding the Hokianga Harbour, also known as the Hokianga River, a long estuarine drowned valley on the west coast in the north of the North Island of New Zealand. The original name, still used by local Māori, is ' ...

s, and French Pass. The harbours produce currents up to 6

knots A knot is a fastening in rope or interwoven lines. Knot may also refer to: Places * Knot, Nancowry, a village in India Archaeology * Knot of Isis (tyet), symbol of welfare/life. * Minoan snake goddess figurines#Sacral knot Arts, entertainme ...

with tidal flows up to 100,000 cubic metres a second. These tidal volumes are 12 times greater than the flows in the largest New Zealand rivers.

Tidal power

Tidal power is generated by capturing some of the energy in the tides as they cycle forth and back, twice each day. Tidal devices can be

weir A weir or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. Weirs are also used to control the flow of water for outlets of l ...

or dam like structures ( barrages), used to hold the tide back, or turbines anchored within the tidal stream. By world standards, New Zealand's tides are, for the most part, moderate. The tide usually ranges between one and two metres. Tidal currents are usually around two kilometres per hour (one knot). Some exception are in and around

, where tidal currents can be much stronger, and at the entrance to some harbours, particularly

.Stevens, Craig and Chiswell, Stephen
''Ocean currents and tides: Tides''
Te Ara: The Encyclopedia of New Zealand, updated 21 September 2007 Headlands and constrictions like these focus the currents, giving energy levels reaching 750 W per square metre.Stevens, Craig; Smith, Murray and Gorman, Richard (2005)
Ocean bounty: energy from waves and tides
' Water & Atmosphere, Vol.13, No.4.

Tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...

s are controlled mainly by the gravitational pull of the moon. About once a day the moon rotates about the earth, attracting as it travels the bulge of water called the

high tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables c ...

that also travels round the earth. There are actually two high tides, because the earth and moon, as a system, both rotate about a common centre of mass. This centre is two-thirds out from the centre of the earth, not at the centre of the earth. 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. A second influence on the tides occurs because of gravitation from the sun. Gravitation from the sun has less influence than the moon, because it is so much further from earth. However, the sun influences the

tidal range Tidal range is the difference in height between high tide and low tide. Tides are the rise and fall of sea levels caused by gravitational forces exerted by the Moon and Sun and the rotation of Earth. Tidal range depends on time and location. ...

. When the sun, earth and moon are aligned in a straight line (at

new New is an adjective referring to something recently made, discovered, or created. New or NEW may refer to: Music * New, singer of K-pop group The Boyz Albums and EPs * ''New'' (album), by Paul McCartney, 2013 * ''New'' (EP), by Regurgitator ...

and

full moon The full moon is the lunar phase when the Moon appears fully illuminated from Earth's perspective. This occurs when Earth is located between the Sun and the Moon (when the ecliptic longitudes of the Sun and Moon differ by 180°). This means ...

), their tidal effects combine, producing the particularly high and low tides called

spring tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ca ...

s. When the sun is at right angles to the moon, the effects are partially cancelled, producing the small tides called

neap tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables c ...

s. New Zealand has a relatively small tidal range, usually less than two metres. 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. Altogether there are sixty-two recognised natural influences on the tides, though only some will be significant at a given location. The gravitation of the moon and sun are the most important. A third influence occurs because the moon orbits at an angle to the equator. This means that if one of the bulges travelling around the earth is above the equator, then the other bulge is below the equator. It also follows that some places will have one daily diurnal tide, while other places will have semi-diurnal tides twice a day. For example, there is a diurnal tide in the

Ross Sea The Ross Sea is a deep bay of the Southern Ocean in Antarctica, between Victoria Land and Marie Byrd Land and within the Ross Embayment, and is the southernmost sea on Earth. It derives its name from the British explorer James Clark Ross who ...

near Antarctica every 24.84 hours. The height of this tide dwindles to almost zero in a cycle which takes 13.66 days. New Zealand's tides are semi-diurnal. The primary cause, the lunar tide, is labelled the M2. The M stands for the moon and the 2 stands for twice a day. A fourth influence occurs because the orbit of the moon around the earth and the orbit of the earth around the sun are elliptical rather than circular. The effect of this is that the time between high tides changes a little from day to day. The moon takes about 24.8 hours to orbit around the earth, so it takes half this time, 12.4 hours, for the M2 tides to occur. The tides can be predicted far in advance, because the moon and earth have orbits that are predictable. The

National Institute of Water and Atmospheric Research The National Institute of Water and Atmospheric Research or NIWA ( mi, Taihoro Nukurangi), is a Crown Research Institute of New Zealand. Established in 1992, NIWA conducts research across a broad range of disciplines in the environmental scien ...

(NIWA) run a tidal computer model specific to New Zealand. The actual tide pattern and timing is determined by the nature of the resonances in each ocean basin with the various frequencies of the gravitational influences, over many cycles. New Zealand's situation (like Iceland's) is a small island in a large basin, and the peaks and troughs of the M2 tides sweep continuously anticlockwise around New Zealand. When it is high tide on the west coast, it is low tide on the east coast, and vice versa: the straightforward notion of tidal bulges aligned with the moon is insufficient. These currents are most noticeable in straits such as Cook Strait and in Foveaux Strait. A notable example is French Pass, just off the greater Cook Strait, where, despite the low tidal range, tidal streams can reach nearly eight knots.

Manapouri

Since the construction of the Manapouri power station, there has been about five MW of tide-determined generation. The tailrace tunnel exit by Dusky Sound debouches at sea level, and thus the effective head of the power station is affected by the level of the tide there. If the turbines are operated at a fixed flow aperture, the power produced is not constant but follows the tide, an effect that can be seen in the following graph. Note that the timing follows the tides around the clock, ''not'' the usual twenty-four cycle of electricity usage. The Opunake power station has its tailrace exiting to the beach but its operation is intermittent so if there is any tidal effect on generation there, it is unclear.

Cook Strait

has tidal flows amongst the strongest in the world, even though it has a smaller tidal range than most places in New Zealand. This is because the main M2 lunar tide component which circulates anti-clockwise around New Zealand is out of phase at each end of the strait. On the Pacific Ocean side the high tide occurs five hours before it occurs at the Tasman Sea side. On one side is high tide and on the other is low tide. The difference in sea level can drive tidal currents up to 2.5 metres per second (5 knots) across Cook Strait as well as into the Tory Channel.Benign tides
Energy NZ No.6, Spring 2008. Contrafed Publishing. An unusual complication is that although there are two spring tides a month on the south side, the north side has only ''one'' spring tide a month, as shown in the plot. A further consequence of these opposed tides is that there is almost zero tidal height change at the centre of the strait. Although the tidal surge should flow in one direction for six hours and then the reverse direction for six hours, a particular surge might last eight or ten hours with the reverse surge enfeebled. In especially boisterous weather conditions the reverse surge can be negated, and the flow can remain in the same direction through three surge periods and longer. This is indicated on marine charts for the region. There are numerous computer model representations of the tidal flow through Cook Strait. While the tidal components are readily realizable, the residual flow is more difficult to model. In April 2008, a resource consent was granted to Neptune Power for the installation of an experimental underwater tidal stream turbine in the strait. The turbine has been designed in Britain and will be built in New Zealand at a cost $10 million. Fourteen metres in diameter and constructed of

carbon fibre Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...

, it will be capable of producing one megawatt. It will be placed in eighty metres of water, 4.5 kilometres due south of Sinclair Head, in waters known as the “Karori rip”. Power from the turbine will be brought ashore at Vector's Island Bay substation. The turbine is a pilot, and will be sited in slower tides for testing. Neptune hopes to generate power from the unit by 2010. The company claims there is enough tidal movement in Cook Strait to generate 12 GW of power, more than one-and-a-half times New Zealand's current requirements. In practice, only some of this energy could be harnessed. On the other side of the strait, Energy Pacifica has talked for some time about applying for resource consent to install up to ten marine turbines, each able to produce up to 1.2 MW, near the Cook Strait entrance to

. They claim Tory Channel has tidal flows of 3.6 metres per second with good

bathymetry Bathymetry (; ) is the study of underwater depth of ocean floors (''seabed topography''), lake floors, or river floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of water ...

and access to the electricity network. No application had been lodged by March 2011. The power generated by tidal marine turbines varies as the cube of the tidal speed. Because the tidal speed doubles, eight times more tidal power can be produced at spring tides than at neap tides.

Kaipara Harbour

The entrance to

, one of the largest harbours in the world, is a channel to the

Tasman Sea The Tasman Sea ( Māori: ''Te Tai-o-Rēhua'', ) is a marginal sea of the South Pacific Ocean, situated between Australia and New Zealand. It measures about across and about from north to south. The sea was named after the Dutch explorer ...

. It narrows to a width of , and is over deep in parts. On average, Kaipara tides rise and fall . At high tide, nearly 1000 square kilometres are flooded. Spring tidal flows reach 9 km/h (5 knots) in the entrance channel and move 1,990 million cubic metres per tidal movement or 7,960 million cubic meters daily.Bellve, AR; Austin, G and Woods, B (2007
Pathway to energy generation from marine tidal currents in New Zealand's Kaipara Harbour
University of Auckland. In 2011, Crest Energy, a power company, received resource consent to install about 200 underwater tidal turbines for the

Kaipara Tidal Power Station The Kaipara tidal power station is a proposed tidal power project to be located in the Kaipara Harbour. The project is being developed by Crest Energy, with an ultimate size of 200MW at a cost of $600 million. Crest plans to place the turbines a ...

, which would use the substantial tidal flows moving in and out every day near the harbour mouth to produce electricity for approximately 250,000 homes. Crest plans to place the turbines at least 30 metres deep along a ten kilometre stretch of the main channel. Historical charts show this stretch of the channel has changed little over 150 years. The output of the turbines will cycle twice daily with the predictable rise and fall of the tide. Each turbine will have a maximum output of 1.2 MW, and is expected to generate 0.75 MW averaged over time. The peak level of generation for the combined turbines is about 200 MW. This exceeds the projected peak electricity needs of Northland. It would have environmental benefits in offsetting annual carbon emissions from a thermal-based, gas turbine generator of 575,000 tonnes of carbon. The project is costed at about $600 million and to be economic would have to be scaled up rapidly to near full capacity.''Harnessing the power of the sea'' Energy NZ, Vol 1, No 1, Winter 2007.
However, while the Department of Conservation has approved the project, and has made substantial environmental monitoring conditions part of the consent, the project also has objectors on the grounds of claimed influences on the local

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...

s and charter fishing. Appeals before the

Environment Court The Environment Court of New Zealand ( mi, Te Kōti Taiao o Aotearoa) is a specialist court for plans, resource consents and environmental issues. It mainly deals with issues arising under the Resource Management Act, meaning that it covers a ...

were concluded in 2010, with a favourable decision released in February 2011.

Wave power

Wave power Wave power is the capture of energy of wind waves to do useful work – for example, electricity generation, water desalination, or pumping water. A machine that exploits wave power is a wave energy converter (WEC). Waves are generated by win ...

involves converting the energy in

ocean surface wave In fluid dynamics, a wind wave, water wave, or wind-generated water wave, is a surface wave that occurs on the free surface of bodies of water as a result from the wind blowing over the water surface. The contact distance in the direction o ...

s into electricity using devices either fixed to the shore, the seabed or floating out at sea. Wave energy varies with time, depending on when and where the winds and storms that drive the waves occur. Tidal energy is more regular and predictable. Two wind zones affect New Zealand. South-east

trade wind The trade winds or easterlies are the permanent east-to-west prevailing winds that flow in the Earth's equatorial region. The trade winds blow mainly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisph ...

s dominate in the north, enlivened an occasional cyclone from the tropics. The rest of the country is dominated by the

roaring forties The Roaring Forties are strong westerly winds found in the Southern Hemisphere, generally between the latitudes of 40°S and 50°S. The strong west-to-east air currents are caused by the combination of air being displaced from the Equator ...

, a broad band of westerly winds that span the middle latitudes of the southern hemisphere. The roaring forties extend over most of the southern part of the

and the

Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...

. These winds produce some of the stormiest seas in the world, with maximum wave heights regularly exceed 4 metres.Stevens, Craig and Chiswell, Stephen
''Ocean currents and tides: Waves''
Te Ara: The Encyclopedia of New Zealand, updated 21 September 2007 On average, ocean waves in New Zealand deliver about 25 kW to each metre of coastline. The west and south-west coasts have the country's most energetic waves. Even on windless days, swells that were generated in the Southern Ocean still arrive. Less wave energy arrives at the north-east coast, because it is sheltered from the south-west waves (click the link on the right for a diagram). The amount of energy in a wave is proportional to the square of its height, so a two-metre wave contains four times the energy of a one-metre wave. Wave Energy Technology - New Zealand (WET-NZ) is a Government-funded research and development collaboration programme between Industrial Research Limited, a Crown Research Institute, and Power Projects Limited, a privately owned Wellington-based company. The programme seeks to develop a wave energy device that generates electricity from both the kinetic and potential energy available in open ocean waves. In 2010 WET-NZ received resource consent for half-scale prototype testing at two test sites. The device is now called Azura and is being tested in Hawaii.

Timeline

* 1966: The world's first tidal barrage project goes online at La Rance, France, with a capacity of 240 MW. * 2003: Seaflow, the world's first underwater turbine prototype, goes on stream off north

Devon Devon ( , historically known as Devonshire , ) is a ceremonial and non-metropolitan county in South West England. The most populous settlement in Devon is the city of Plymouth, followed by Devon's county town, the city of Exeter. Devo ...

with a peak capacity of 300 KW. * 2008: The world's first commercial

wave farm Wave power is the capture of energy of wind waves to do useful work – for example, electricity generation, water desalination, or pumping water. A machine that exploits wave power is a wave energy converter (WEC). Waves are generated by wind ...

goes on line in Portugal. It uses Pelamis devices and has a peak capacity of 2.25 MW. * 2008: SeaGen, the world's first commercial scale tidal stream energy generator, goes on stream in

Strangford Lough Strangford Lough (from Old Norse ''Strangr Fjörðr'', meaning "strong sea-inlet"PlaceNames N ...

, Northern Ireland with a peak capacity of 1.2 MW.Tidal power in the UK: SeaGen
/ref> * 2008: Crest Energy Kaipara Limited applies for resource consent to sink 200 marine turbines near the entrance of

, with a peak capacity of 200MW. * 2008: Neptune Power given resource consent to build a pilot turbine off Sinclair Head in

. * 2008: Energy Pacifica applies for resource consent to install up to 10 marine turbines, each able to produce up to 1.2 MW, near the Cook Strait entrance to

References

External links

Ocean Energy Review 2008

Video: Chasing currents (NIWA)

– J Floor Anthoni, 2000.
WET-NZ
(Wave Energy Technology - New Zealand)

Publications {{Ocean energy

Renewable energy in New Zealand Articles containing video clips