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Who owns Crest Energy?
Has Crest consulted with the local community?
Is tidal energy much more expensive than existing NZ hydro electricity?
If the project fails, who will return the harbour to its current state?
How is the environment being looked after?
Will the project benefit the local economy?
Where tidal technologies are deployed today?
Will snapper stocks be damaged?
How big are the turbines?
What's the history?
How did this all start?
Can I see a map?
Where else in the world is tidal electricity an option?
What are the commercial risks in this project?
Does the project attract government support?
Why the Kaipara and not other harbours?
How will the project be monitored?
How does tidal energy's carbon footprint compare with other energy sources?
How big is the Crest Kaipara Energy Project?
Will the project create jobs in New Zealand?
How do I register as a supplier to Crest Energy?
Can I get a job at Crest Energy?
How do the currents go in and out of the harbour?
Will the turbines get covered in barnacles?
How will the turbines be kept in position?
Will the turbines rust quickly in sea water?
If the turbines are seven metres underwater, can a storm destroy them?
Where are the 100 shipwrecks?
Will the turbines damage dolphins?
Will the turbines damage birds?
Will the project harm fishing?
Will the turbines prevent access to leisure craft?
Will the cables cause problems anchoring, or to animals?
What happens if the main channel changes?
What happens if the cables break?
Why do the turbines need so much space?
What is resource consent?
How will the turbines be kept in place on the harbour floor?
What is the difference between megawatts and megawatt-hours?
How much electricity can one marine turbine produce?
What happens when the tide is slack and not moving?
Can I buy 'green', renewable electricity for home?
Why use DC power (rather than AC)?
What sort of cable will be used?
Why do you need a substation?
What happens to the turbines if the project fails?
Who are the main generators in New Zealand?
Are these turbines viable?
How about a tunnel between Manukau Harbour and the Hauraki Gulf to power turbines based upon the tidal differences between the two bodies of water?
How do electricity prices in New Zealand compare internationally?
How do tides work?
What are the differences between the 2006 and 2007 RMA applications?


Who owns Crest Energy?

Over 99% of the shares are owned by New Zealanders.


Has Crest consulted with the local community?

Crest undertook a major consultation programme with key stakeholders. Judge Newhook of the Environment Court noted in his December 2009 Interim Decision that '... attempts by Crest to consult were extensive, considerable and meaningful ...'.

Crest held well over 100 consultative meetings over five years with interested parties.

The consultations included those with the Auckland Regional Council, Northern Regional Council, Rodney District Council and Kaipara District Council.

Representatives of Environs Holdings on behalf of Te Uri o Hau provided Crest with a Cultural Impact Assessmentdocument outlining their understandings of the project and its potential impact on their community and the harbour.

Crest also attended hui and met with many other interest groups and individuals.

Many companies have expressed interest in the commercial and economic opportunities which may be created in and near the Kaipara by the project, and have also met with Crest.

As a result of the consultation processes Crest withdrew its July 2006 consent applications and made revised applications in July 2007 which incorporated modifications arising from community and stakeholder feedback.

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Is tidal energy much more expensive than existing NZ hydro electricity?

It is not possible to directly compare the pricing of tidal and hydro generated electricity as there are many different considerations to take into account e.g. a major percentage of the hydro generation system is from legacy state-funded developments, some of which are more than 50 years old - if these had to be built today it would be at very significant cost in real terms, with consequent implications for power pricing.

The price comparison of tidal power is not against legacy hydro schemes but against new fossil fuel based power stations where typically the new gas supply is very much more expensive than many people imagine, as is the electricity generated by such new stations.

Another consideration is that we have reached maximum capacity of available resources, and the pricing of new generation capabilities to meet the rising demand for electricity in New Zealand. For a secure and sustainable future we have to develop renewable resources. We simply cannot afford not to.

What we can say about the cost of tidal power is that it provides predictability of supply, enabling smoothing, optimisation and management of resources. This means that it will be less subject to the external price fluctuations we see with other sources of power. If anything tidal turbines will depress the spot electricity price, not inflate it.

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If the project fails, who will return the harbour to its current state?

Both the original 2008 Northland Regional Council recommendations and those of the 2011 Environment Court decision contain conditions for a large financial bond.

The purpose of the bond is to provide for the removal by independent contractors of materials related to the project from the harbour, should the project be abandoned after construction begins. The bond is automatically adjusted for inflation and there are specific conditions in place for the periodic review of the size and purpose of the bond.

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How is the environment being looked after?

This project has evolved through five years continuous research and investigative processes, in which a key focus has been to identify any potential effects on the harbour environment.

The rigorous Environment Court process ensured extensive analysis, debate and input from independent experts, Tangata Whenua and interested parties. The consent conditions provide for extensive monitoring and assessment throughout staged development of the project.

The Environment Court's project conditions, and in particular the Environmental Monitoring Plan, has 103 pages of detailed monitoring requirements and identifies responsibilities and processes for the initial and continuous obligations imposed under the consent.

The EMP was developed jointly over several years in consultation with stakeholders, the Northern Regional Council, the Department of Conservation, interested parties and experts giving evidence to the Environment Court.

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Will the project benefit the local economy?

We intend to incorporate as much NZ content as feasible and Crest intends to source and manufacture locally when possible.

The development of competitive local supply chains into a major project will have substantial economic benefits.

Crest volunteered to fund a significant “Crest Energy Kaipara Trust” for the benefit of the health of the harbour. Community trustees will be needed once the project is in operation to manage the trust on behalf of all users of the Kaipara.

A 2006 study carried out by Business and Economic Research Ltd (BERL) for the Industry Capability Network (a unit of NZ Trade and Enterprise), established that every $1 million spent in manufacturing activity in New Zealand generates an extra 11 jobs, NZ$117,000 tax revenue, $195,000 of purchasing power and $119,000 saving of government welfare payments.

We estimates total potential expenditure of around NZ$600 million during the first ten years of the project. Many of the skills needed for the project are common to ship building and large construction projects. This is potentially a substantial capital injection into Northland Region’s population of 160,000 people.

A generally agreed average for large projects is that expenditure is equally split across the region, nation and internationally. If these averages hold true for the Kaipara project over the first ten years of the project, about $200 million will be spent in Northland and Auckland, a further $200 million nationally and the balance overseas.

Some components of the project are not available and are unlikely to be available in NZ such as submarine electrical cabling, complex electrical control equipment and turbine technologies.

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Where tidal technologies are deployed today?

There are deployments of marine tidal turbines including those in Norway, Northern Ireland, USA, Canada, Australia, South Korea and Scotland. Large international technology companies are investing their capital and engineering expertise in tidal technologies.

We recognise that there are concerns about the implementation of new technologies: however there is widespread international recognition of the significance of the ocean energy sector, which is supported by high levels of investment and commitment to the development of this energy source in many countries.

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Will snapper stocks be damaged?

A NIWA scientist and expert witness for the NRC during the Environment Court hearing indicated that his opinion was that there is a low risk that the project would adversely affect snapper and fisheries. His evidence was given in the context of other research showing the importance of the Kaipara harbour to the north-western New Zealand fishery.

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How big are the turbines?

Bearing in mind that consents are for a period of 35 years, the company applied for the maximum possible size of turbine that could fit in the harbour mouth.

This does not mean that large turbines will be installed immediately: it means Crest is taking heed from some other projects (particularly wind) where permits were gained for small turbines which subsequent technological developments made redundant.

Most turbines being built today are ten metres in diameter, although some of the latest designs are as large as 17 metres. Potentially Crest’s could be as large of 25 metres, sited invisibly seven metres below the surface of the water in water 31-52 metres deep.

Crest has not yet made a decision on the initial supplier or suppliers of turbines for the project.

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What's the history?

July 2005
  • Company incorporated, consultation with the local communities and project investigations begin
July 2006
  • First applications for permits
December 2006
  • Public submissions for and against the Kaipara project for Northland Regional Council, Auckland Regional Council and Rodney District Council.
January 2007
  • Public submissions closed on 12th January 2007
  • Council officers review application material and submissions received, and Crest provides further information requested by Council officers (these are called S92s; other s92’s were answered in November 2006)
June 2007
  • As part of Crest's extensive consultations with Tangata Whenua, representatives of Environs Holdings on behalf of Te Uri o Hau provided Crest with an extensive and carefully prepared Cultural Impact Assessmentdocument outlining their understandings of the project and its potential impact on their community and the harbour
July 2007
  • Crest applies for adjusted consents in response to public submissions received in January 2007.
  • The revised applications require less marine cabling (33 to 7 kilometres), occupy less space in the harbour (1,300 to 350 hectares) and place turbines deeper below the surface of the sea (7 to 5 metres).
  • The new applications also mean that previous applications with Rodney District Council and the Auckland Regional Council are no longer required.
  • Kaipara District Council pursuant to Section 139 of the RMA certify that the overland reticulation of power generated by the project is a permitted activity as defined in the District Plan
September 2007
  • Second round of public submissions to the applications closed (about 123 in favour, 121 against)
October 2007
  • Northland Regional Council begin writing the Staff Report, a detailed consideration of the Project
  • Three independent Commissioners form a panel to consider the evidence for and against the applications
November 2007
  • The Invitation to eligible investors to apply for shares in Crest Energy Limited dated September 2007. This offer was not open to the general public. Interested potential investors should visit our Investors page.
May 2008
  • Marine Energy Deployment Fund first NZ$1.85 million grant awarded to Crest by the Minister of Energy, subject to the granting of consents for the project.
  • Five days of regional authority Hearings
August 2008
  • The Northland Regional Council recommends that the Minister of Conservation approve a staged tidal power plant in the Kaipara Harbour.
September 2008
  • Two parties launched appeals to the Environment Court requesting the project be declined in its entity. Two further appeals centre around consent conditions rather than objections to the entire project.
June 2009
  • Appeal by Environs Holdings to the Auckland High Court to delay Environment Court Hearings denied.
  • The Environment Court convened in Whangarei under Judge Newhook to consider Crest's applications for resource consents. Over 30 expert witnesses offered evidence.
July 2009
  • Leading New Zealand energy producer and retailer Todd Energy takes cornerstone stake in Crest Energy. Todd Energy owns and operates its own natural gas, oil, LPG, electricity, cogeneration and solar hot water heating assets, enabling it to manage the flow of energy from exploration and production for its industrial, commercial and residential customers. Todd Energy has significant investments in renewable generation developments including hydro, geothermal and landfill gas energy plants. Todd Energy is also the largest generator of electricity in New Zealand from efficient gas-fired co-generation facilities.
December 2009
  • The Environment Court’s interim decision indicated a possible positive recommendation for the project subject to some additional fact finding and the preparation of a draft environmental monitoring plan.
May 2010
  • A second Invitation to eligible investors to apply for shares in Crest Energy Limiteddated 23rd April 2010. This offer was not open to the general public. Interested potential investors should visit our Investors page.
August 2010
  • Crest filed further documents with Environment Court participants following extensive additional consultation with experts on mainly two subjects: the detailed Environmental Monitoring Plan for the project, and the impact (if any) of the Project on snapper.
February 2011
  • The Environment Court recommended that the Honourable Kate Wilkinson, Minister of Conservation, approves Crest's applications for the development of a tidal power station
March 2011
  • New Zealand's Minister of Conservation approves Crest's applications
August 2011
Onwards
  • Crest raises pre-construction capital
  • The total funding requirement is over ten years is perhaps NZ$600 million
  • Capital will be raised in stages corresponding to project milestones
  • Generation of up to 200 MW is planned for 2023

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How did this all start?

The company was founded in July 2005. The idea is not new: the Auckland Chamber of Commerce lobbied unsuccessfully for tidal power in the 1920's. Please see Auckland’s Voice of Business: A history of the Auckland Chamber of Commerce 1856-2006 chapter 3 page 51.

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Can I see a map?

For photographs, maps and diagrams, please see our Gallery .

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Where else in the world is tidal electricity an option?

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What are the commercial risks in this project?

The risks are similar to any large infrastructure project. Additional considerations for the Crest Kaipara Energy Project are:

  • Financial: will Crest Energy secure sufficient capital to execute the project?
  • Management: will Crest Energy attract the right people to complete the project?
  • Forecasting: future cost of funds and future wholesale electricity price path
  • Environmental: the adaptive management regime and the environmental conditions under which the project's consents are granted prove too arduous
  • Technical: will the combinations of turbines and cables work to specification?

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Does the project attract government assistance?

Ex-Prime Minister Helen Clark launched the New Zealand Energy Strategy which includes a target to generate 90% of electricity from renewable resources by 2025, and to limit the construction of new fossil fuel generation plants for a decade. Current renewable output is about 60% of supply. There is limited scope for further large scale hydroelectric power generation. Geothermal and wind are well positioned and newer technologies such as wave and tidal were mentioned by the government: Crest Energy is named in the announcements. Meanwhile NZ Maui gas supplies used for electricity generation are running out and an alternative, the importation of LPG, would be even more expensive than renewables, according to Ministers.

A particular issue for northern NZ is that most electricity supply flows from south to north, and through the Auckland isthmus. The government has stated that it does not support a proposed gas plant north of Auckland near Helensville, close to Kaipara Harbour. Although there are many small initiatives to generate electricity north of Auckland, at this stage it would seem the Crest project may be valuable both for grid stability and security of supply to the north, once and if it comes on stream.

The Emissions Trading Scheme is good news for the Project. It may mean that the spot market electricity price line rises by about 10% over time. In addition Crest may provide VER's which are likely to trade at a discount to Kyoto carbon credits.

In May 2008 Crest Energy was awarded NZ$1.85 million from the New Zealand Marine Energy Deployment Fund (185 KB)by the Energy Minister. The NZ Energy Efficiency and Conservation Authority (EECA) administer the fund on behalf of the Minister of Energy. The award is subject to a rigorous set of milestones. The NZMEDF runs for four years and offers a maximum of NZ$8 million: the award to Crest is the maximum available in the first year and the funds can only be used for turbine construction and installation.

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How will the project be monitored?

Monitoring is an important component of the Project. Monitoring data will be evaluated by the consent authority (Northland Regional Council) under Section 128 of the Resource Management Act, before the start of each stage of the project. Monitoring will also occur continuously during operation of the power station.

Two years of baseline data will be collected prior to the Stage 1 deployment, with monitoring continuing during Stage 1 and for a minimum of 12 months after completion of Stage 1 prior to initiation of Stage 2. A similar process will apply for the transition between later stages. The stages are for 3,20, 40, 80 and 200 turbines.

Monitoring before, during and after installation of the various stages would allow verification of the level of actual environmental effect, would enable adverse effects to be determined and would provide a basis for measures to avoid, remedy or mitigate any such adverse effects as appropriate.

Monitoring will include a wide range of environmental parameters and monitoring of the integrity of the turbine structures themselves. Specific aspects to be monitored will include:

  • Energy extraction through the tidal current devices
  • Interactions with tidal flow patterns, localised currents, sedimentation processes and seabed bathymetry and morphology
  • Effects of support structures on the wave and tidal dynamics, possible implications for local sedimentation and seabed movement, geotechnical and geological aspects
  • Effects of the rotor interactions on the water column and the subsequent effects on seabed morphology
  • Observed collision risk for marine life
  • Acoustic emissions and the potential implications involved with respect to marine mammals and other marine ecology, such as fish
  • Vibration characteristics
  • Overall ecological impacts and benefits of installation and operation
  • Recreational, commercial and non-commercial use of the harbour

Detailed monitoring protocols are contained within the 103 pages of consent conditions agreed by the Environment Court within the Environmental Monitoring Plan.

The EMP was developed jointly in consultation with stakeholders, the Northern Regional Council, the Department of Conservation and experts giving evidence to the Environment Court.

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Why the Kaipara and not other harbours?

The Kaipara Harbour has the biggest tidal flows in New Zealand and is one of the largest harbours in the world. During spring tides the current in the Kaipara can exceed 9 kph (nearly five knots).

The next four New Zealand harbours are Manukau, Hokianga, Whangarei and Waitemata. The Kaipara has over double the tidal flow of Manukau. Additional attractions of the Kaipara are the lack of commercial shipping, proximity to Auckland north of the isthmus, and relatively low leisure usage of the harbour mouth.

The depth of the harbour mouth channel, where the turbines will be located, is an asset: neither too deep for access by divers if needed (31 metres to a maximum 52 metres), nor too shallow and therefore impacted by lack of water at low tide. The sandbar surrounding the mouth protects the project from oceanic waves.

Harbour Water volume Average current
  Millions of cubic metres Metres/second Kilometres/hour Knots
Kaipara 1,990 1.12 4.0 2.20
Manukau 918 0.92 3.3 1.80
Hokianga 228 0.81 2.9 1.60
Whangarei 164 0.54 1.9 1.00
Raglan 46 0.59 2.1 1.10
Hume and Herdendorf, 1992, 1993; and Hicks and Hume (1996)

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How big is the Crest Kaipara Energy Project?

Crest's output would provide power for the equivalent of 250,000 NZ homes. Crest aims to generate about 3% of New Zealand's industrial, commercial and residential electricity needs. Demand is expected to rise 2% annually across the country and 5% or more north of Auckland.

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How does tidal power's carbon footprint compare with other energy sources?

In 2007 CREST provided some funding assistance two University of Auckland environmental engineering students to research the full life carbon cycle of four NZ sustainable energy sources: tidal, wind, hydro and geothermal. Their findings are summarised below:

Full life carbon Embodied energy Kilo joules per kilowatt hour Carbon dioxide emissions Grams of CO2 per kilowatt
Tidal 42 1.8
Wind 70 3.0
Hydro 55 4.6
Geothermal 105 6.3
Combined cycle gas N/A 200-300
Coal N/A 400-1,000

The study found that tidal is amongst the cleanest (in CO2 terms) of renewable electricity sources. Wind is less predictable and consistent, increasing the footprint. Hydro uses huge amounts of energy for the steel and concrete in the dams and waterways, and for the energy used initially for vegetation clearance and roads. Geothermal uses high quality of materials with high energy contents to operate in hostile geothermal environments and the materials require frequent replacement.

Coal and gas produce hundreds of times more emissions than renewable sources.

NZ national average emissions are about 210 grams CO2 equivalent per KWh which is internationally low due to the high contribution of hydro to NZ electricity production. Figures for Huntly coal are 958 g CO2/KWh and Otahuhu B gas 372 g CO2/KWh, according to Energy Modeling Consultants Ltd November 2008 report.

Tidal energy short and long term marginal costs seem economically similar to those of wind power, and those of tidal energy can only improve as more turbines are deployed around the world.

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Will the project create jobs in New Zealand?

General averages suggest that large projects create jobs locally, nationally and internationally in roughly equal proportions. The Crest project could involve NZ$600 million of expenditure over the first ten years of the project.

Figures from the Industry Capability Network, part of NZ Trade and Enterprise, suggest that eleven jobs are created by each NZ$ million invested. Furthermore government expenditure on unemployment benefit declines by NZ$118,000, government income tax revenue increases by NZ$117,000 and there is an increase in purchasing power of $195,000.

Crest Energy does not currently have agreements in place concerning recruitment and the supply of products and services.

Consideration of potential suppliers may commence in late 2011.

At present Crest's plans for roles include:

Monitoring
  • Several phases of detailed biological and environmental monitoring of the site before, during and after construction
Depot
  • Turbine fabrication and assembly, land-based maintenance, docking for marine craft
Materials
  • Steel, cables, composites, ballast, concrete, electrical equipment, marine equipment, barges and boats
Crews
  • Fabrication, assembly, installation, commissioning, maintenance and monitoring of equipment offshore and on land
Substation
  • Construction, commissioning, operation and maintenance; transformer, converter and cooling equipment
Cable
  • Trenching, installation, commissioning and maintenance
Markers
  • Installation and maintenance of navigational markers
Scoping
  • Professional services for the scoping of the project
Core team
  • Provision of support for the day-to-day operation of the project

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How do I register as a supplier to Crest Energy?

Crest Energy is not yet ready to talk with potential suppliers.

Crest Energy does not currently have agreements in place concerning recruitment and the supply of products and services.

Consideration of potential suppliers may commence in late 2011.

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Can I get a job at Crest Energy?

Not yet.

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How do the currents go in and out of the harbour?

Detailed current measurements using GPS drogues show the flows in the Kaipara depending upon the tidal cycle (spring to neap). The flow is slightly asymmetric meaning that the ebb and flood are not exactly opposite in flow directions. The tidal current varies between 1.6 and 2.5 metres per second (up to nine kilometres per hour or five knots). The areas of strongest current are on the western end of the harbour mouth.

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Will the turbines get covered in barnacles?

The tidal current varies between 1.6 and 2.5 metres per second (up to nine kilometres per hour or five knots). The seawater carries sand particles in suspension from harbours and rivers south of the Kaipara, which is why there are huge sand hills and sand extraction activities around the Kaipara. The sand will help keep the turbines clean and reduce biofouling. Sand falls out of the water flow and form deposits when the current drops below 0.3 metres per second suggesting that the turbines will not suffer from sand sedimentation around them. The photo shows how much sand there is (the dunes are about 120 metres or 400 feet tall)!

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How will the turbines be kept in position?

There is a firm footing for turbines in the harbour mouth. Sonar sidescans, CCTV video footage, dredge samples and samples taken from the harbour floor in the turbine area by commercial divers suggest the floor is very hard and made up of either bare scoured sandstone, or densely packed large grain sand on a deeper bed of sandstone. The divers used a water pump and lance, sheer vane gauge and hand penetrometer to assess the nature of the harbour floor. The divers also noted that visibility is extremely poor, or zero, in the main channel.

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Will the turbines rust rapidly in sea water?

All materials corrode to varying degrees. A highly corrosive combination is the oxygen in air, and sea water. Turbines are submerged with much less oxygen than in air, which should give them a long life. Parts of the turbines will need replacement each decade. The turbines will be subject to regular maintenance.

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Will the turbines damage dolphins?

Turbine rotors turn slowly at about six revolutions a minute and are shielded. The speed of the rotors depends upon the speed of the current and the pitch of the turbine blades. A turbine with a blade radius of nine metres has a space between successive rotating blade tips of about 11 meters. Marine mammals and fish sense and avoid obstacles (Southern Right whale, NZ sea lion, orca and dolphin). Dolphins are agile, communicative, have excellent eye sight and echolocation. Crest believes the risks are minimal for dolphins. The turbines will provide new areas for fish and other life in the harbour mouth. Sharks, rays and skates are also important and although many people think they are slow and unresponsive, they show remarkable agility and power to move fast when necessary.

Turbines are almost silent and should not, therefore, distract animals from their travels, particularly bearing in mind the high baseline noise from the sandbars surrounding the harbour mouth.

See the NZ Department of Conservation guide to marine mammals for more information, and the NZ Encyclopedia which covers sharks, rays and skates.

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Will the project damage birds?

Huge numbers of wading, migratory and resident birds live in and around the harbour. The cables are sited to avoid sensitive areas such as seagrass (eelgrass) beds and tubeworms habitats. Away from the main channel the cables will be in sand and buried. The turbines may in fact increase the supply of fish for birds by providing fish breeding sanctuaries in the slower water at the base of the turbines. The panorama photo below contains thousands of wading birds.

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Will the project harm fishing?

There is a rumour circulating that fishing from the shore, and fishing in the harbour, will be banned: this is not true.

Consultations indicate that a key fishing area is around the mussel beds in known as the Graveyard, presumably named because of the many shipwrecks in the area. Crest's side-scan sonar surveys identified the location of the mussel beds and nature of seabed in the turbine array area. The turbines will be located to greater than 31 metres depth which provides separation from mussel beds, and mostly avoids the primary areas of fishing use since the mussel beds are in shallower water.

Longer term Crest Energy do not think the project will reduce the enjoyment of anglers. Consultations suggest that the area of the turbines is seldom used for fishing, even at slack water due to the depth of the channel of up to 52 metres.

During ebb and flood water the turbine area is dangerous and anchoring difficult for leisure craft. The fishing that does take place near the turbine area is sited closer to the shore near the escarpment that runs east-west along the main channel, or further out to sea.

A point to note is the differences between the old and new RMA applications made in response to concerns expressed in public submissions to the project up until 12th January 2007. The original outlined a cable running east-west across the harbour for over 30 kilometres, whereas the new route is about 7 kilometres from the array area to Pouto Point. This enormously reduces the footprint of the Project and the level of impact on fishing activities.

There are indications from structures used in offshore oil and gas fields to suggest that fish stocks and bio-diversity will be improved by the presence artificial sanctuaries. In other words, over several years Crest believes the turbines will make a significant and positive contribution to maintaining the biodiversity and richness of the Kaipara harbour.

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Will the cables cause problems anchoring, or to animals?

The Kaipara is over 738 square kilometres and Crest Energy has applied to occupy a tiny fraction of the area. A pair of cables will run seven kilometres from the harbour mouth to Pouto Point on North head. The cables will be buried one metre below the harbour floor. The harbour floor along the route is usually sand, according to Crest's initial survey. Leisure craft will be able to anchor over the cable but will be restricted from anchoring or passing over the turbine area. The cables are both buried and shielded. Similar cables are used all over the world.

The cables will carry DC electricity which is important since the electromagnetic interference is 5% of the impact for AC. Sharks, rays and skates are particularly sensitive to high electromagnetic levels. The burial process itself will cause short term disruption to harbour floor animals and plants. The cables are about 125 millimetres in diameter.

A second type much smaller cabling will link the turbines together and join with the main submarine cable at one or more hubs. Each array or loop will manage between 10 and 30 turbines.

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What happens if the main channel changes?

Early European maritime charts date from the middle of the 19th century. The main channel through the harbour mouth, where Crest plans to place turbines, does not appear to have moved in 150 years. Although the sandbars clearly shift, their overall position has not changed.

The cables include a fibre optic strand. Changes in pressure and tension can be measured accurately and Crest will be alerted quickly to movements on the harbour floor, and issues with the cables. In this event Crest can either move the cables and bury them elsewhere, or cover them with harmless ballast, or use a kind of blanket to shield the eroded area. The marine chart below shows the main channels.

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What happens if the cables break?

The cables are buried over one metre below the harbour floor in sand. If the cables are broken, as has happened for a variety of reasons with other marine cables, repair should take 48 hours.

Locating the break is done using feedback from the fibre optic strand in the cable which measures changes in tension and pressure. Weather conditions inside the Kaipara do not present additional hazards such as ice and large waves.

The most common insurance claim by offshore wind farms in Europe is for cable damage caused usually by commercial vessels. The Kaipara harbour has very limited commercial vessel activity confined to sand mining barges on the eastern edge of the harbour.

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Will the turbines prevent access to leisure craft?

The turbines will be positioned seven metres below low water (about 23 feet), meaning that leisure craft can pass over the turbines but for safety reasons access to the turbine area will be restricted. The harbour mouth is nearly six kilometres wide and the turbines will occupy a small part of the width.

The turbines will be limited to the 31 metre contour and below of the deep water channel. Commercial traffic, apart from sand barges, is minimal due to the dangerous sandbars at the harbour mouth and the low population of the catchment area. The sandbars outside the harbour mouth offers about five metres draught at low tide: therefore few large craft attempt to enter the harbour.

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If the turbines are seven metres underwater, can a storm destroy them?

The prevailing weather on the Tasman is from the south west and storms are common. However the turbines are protected from the full impact of oceanic conditions by the sandbars that surround the harbour mouth. The sandbars limit navigation to vessels with under five metres draught. Parts of the sandbars are exposed at low tide.

There are over 100 documented shipwrecks around the sandbars. The area in which Crest will install turbines is calmer with the largest waves at about 1.50 metres. The first photograph below is unusual since the waves were created by the current (standing waves), and not by the action of wind or waves from out to sea.

Conditions in the harbour mouth can be very dangerous for smaller craft in particular when high winds blow in the opposite direction to the tidal flow, causing choppy seas that can flood a small boat.

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Where are the shipwrecks?

The Kaipara, like many harbours around New Zealand, is hazardous for shipping. According to Maritime New Zealand there are three types of harbour bar - dangerous, very dangerous and lethal - the Kaipara Harbour is no exception.

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What is the difference between megawatts (MW) and megawatt-hours (MWh)?

A watt is the unit rate at which work is done in an electrical circuit. An incandescent light bulb typically has a power requirement of 100 Watts.

kilo watt (kW) = 1,000 watts
mega watt (MW) = 1,000 kW
giga watt (GW) = 1,000 MW

One watt-hour is equivalent to one watt of power consumed or generated continuously for one hour. The average New Zealand household consumes 8,000kWh or 8MWh of electricity annually. This is an equivalent amount of power used by 2kW electric kettle switched on for six months. Houses in the north generally consume less electricity that those in the south, due to the warmer climate. Over half of domestic electricity consumption is for hot water heating.

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How much electricity can one marine turbine produce?

The amount of power each turbine will produce depends on the speed of the tidal flow, the size of the turbine rotor, the tidal cycle and the efficiency of the design. There are nearly two high tides and two low tides each 24 hours in the Kaipara. Each turbine will be in action for about 14 hours each day.

Spring tides generate more flow than neap tides, and the outgoing or ebb tide is more powerful than the incoming or flood tide. Wind, air pressure and rainfall in the catchment area also play a role in determining the speed of the tidal current. On average each turbine is expected to generate 0.75 MW. The formula is :

P = ½dAV3Cp

d = density of seawater (1.025 kg/m3)
A = swept area of the blades (m2)
V = velocity of the currents
Cp = power coefficient

Thus the current speed and blade radius are the major factors determining power output. Water is non-compressible and 830 times denser than air which also contributes to the high power output. Crest also knows that the ebb tide is not exactly the opposite of the flood tide. The Venturi shroud accelerates both flood and ebb currents. The output is enhanced further by currents entering the turbine off-centre through to an angle of 38°. In other words, the asymmetry of the currents is good news, even if this seems illogical.

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What happens when the tide is slack and not moving?

Marine turbines depend upon the current and slack tide means that generation will be minimal. The turbines will be arranged over a large distance and bathymetry surveys suggest that minor flows are always present. Nevertheless, for the 15 hours a day when there are tidal flows we can accurately predict the total output and sell that output effectively to complement other power sources. Currents range up to 2.5 metres per second (5 knots or 9 kph) and electricity generation should begin from about 0.7 metres per second of tidal flow.

Electricity systems manage major fluctuations in demand through the day and seasons. Any system must be capable of responding to these fluctuations. Relative to fluctuations in demand, those that occur due to changes in output of marine turbines are minor.

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Why do the turbines need so much space?

Further detailed work will determine the exact positioning of the turbines. They will be seven metres or more below the surface, silent and invisible. The turbines will be arranged in groups or arrays for technical reasons.

The turbines need to be apart from one another, and the groups well separated, to avoid interference and to maximise the yield from the current. Fluid dynamic studies suggest the groups need to be up to 500 metres apart, and we know that the main deep channel is narrow.

The direction of flood tidal current frequently is not always 180° from those of ebbing currents. The result is a requirement for about 8,000 metres of distance along the channel in order to position 200 turbines, and maintain the economic viability of the project.

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What is resource consent?

Resource consent allows a person or organisation to do something which may have an effect on the environment. For example, consent may be required before you discharge waste into the environment, divert a stream or build a bridge, clear vegetation or place a mooring, undertake earthworks or build a house. Crest Energy submitted multiple applications pursuant to section 88 of the Resource Management Act 1991 in 2006/7, which were processed by Northland Regional Council. Permits eventually granted by the Minister of Conservation in March 2011.

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How will the turbines be kept in place on the harbour floor?

The weight of the turbines and ballast will keep the turbines in place. There are several options for the exact engineering process but it is likely that quarried rock from the north east of the Kaipara Harbour will be brought in by barge to act as ballast.

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Can I buy 'green', renewable electricity for home?

In New Zealand electricity must be purchased from the electricity generators. Some generators are greener than others.

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Why use DC power (rather than AC)?

Large offshore wind farms over 100 MW generally use HVDC (High Voltage Direct Current) because DC technology :

  • emits about 5% of the electromagnetic radiation of AC which is good for elasmobranchs (sharks etc)
  • is economically viable for large MW power transfer over long distances to market
  • immune to types of faults associated with high voltage AC generation and transmission
  • allows power transfer oscillation between nil MW to 200 MW to nil MW over 6 hours
  • Gives capacitive re-charging of 100 km whereas HVAC cables would pose a significant
  • limitation
  • matches voltage and current performance to periodic oscillatory nature of tides
  • not reliant on grid for synchronisation or reactive power-energy compensation
  • has a history to the 1870's for reliable operational service
  • Requires two submarine cables versus three larger cables for HVAC equivalent power ratings

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What sort of cable will be used?

Crest will use cables similar to those running under the Cook Straight which were installed in the early 1960's to bring hydro power from the South Island to the North. The bipole HVDC cables are waterproof, salt corrosion resistant, solid plastic polymer, insulated copper with high mechanical strength. The cables are about 125 millimetres in diameter and buried over one metre under the harbour floor. Crest does not believe that buried DC cables will have any impact on marine navigation equipment.

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Why do you need a substation?

A substation will be sited at Northpower's existing Ruawai facility, opposite the school. The new building is similar to a large agricultural shed. It will be insulated for sound and trees and shrubs planted to minimise the visual impact. The building will house HVDC/HVAC converter equipment. The volume of converter equipment will grow as turbines are installed.

Cables will link the indoor converter to the outdoor substation within the existing fenced compound.

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What happens to the turbines if the project fails?

Both the original 2008 Northland Regional Council recommendations and those of the Environment Court contain conditions for a large financial bond.

The purpose of the bond is to provide for the removal by independent contractors of materials related to the project from the harbour, should the project be abandoned after construction begins. The bond is automatically adjusted for inflation and there are specific conditions in place for the periodic review of the size and purpose of the bond.

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Who are the main generators in New Zealand?

The major generating companies (three State-Owned Enterprises (SOEs) and three private sector companies) are:

Some generators are greenerthan others.

Smaller generation exists, most of which is associated with industrial processes. Generation companies own and operate power stations. Most of New Zealand’s electricity is generated at remote locations and requires an efficient transmission system to transport it to the main demand centres. Around 40 sites supply electricity to the national grid. Some of the smaller scale generation is 'embedded' and feeds directly into local distribution networks.

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Are these turbines viable?

According to the investment bank Goldman Sachs 49 governments around the world provide incentives for sustainable energy projects. Wind power is now mature, and tidal turbines are well funded in Europe. The US government recently offered US$50 million in support of marine energy development. The UK government has spent perhaps GBP 50 million on marine energy. There are about a dozen companies offering marine turbine solutions. Some observers believe tidal power is at roughly the same stage of development as wind power was a decade ago. The NZ government has introduced a carbon emissions trading scheme, a Marine Energy Deployment Fund and released its Energy Strategy to 2050.

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How many people made submissions?

There were are remarkable number of people actively in support of the project on the two rounds of public submissions of January 2007 and September 2007.

Often 90% or more of submissions are in opposition to RMA applications. However in the case of this project the supporters and opponents are about equal in number. Within the submissions of those opposed, many are concerned with a possible reduction in recreational and charter fishing. Crest Energy has tried to address the fishing worries by moving to deeper water away from mussel beds, eliminating the trans-harbour eastern cable route in favour of a shorter route to Pouto Point, and occupation of a smaller area in the harbour.

View Number Percentage
Support 123 49.6%
Oppose 121 48.8%
Other 4 1.6%
Total 248

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How do electricity prices in New Zealand compare internationally?

New Zealand has enjoyed some of the cheapest electricity prices in the world. As a result, conservation of energy, fuel efficiency and domestic insulation have been low priorities. Rising demand, declining output from the Maui gas field and changes in energy views have seen rapid price rises.

Nevertheless the price of electricity remains one of the lowest in the OECD. There is broad agreement that prices will continue to rise steadily because new, clean energy sources are in short supply. An Emissions Trading Scheme was announced by the government in September 2007 is likely to increase energy prices.

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How about a tunnel between Manukau Harbour and the Hauraki Gulf to power turbines based upon the tidal differences between the two bodies of water?

Many people have suggested a tunnel between the Manukau Harbour and Hauraki Gulf to power turbines based upon the tidal differences between the two bodies of water. The concept is common in freshwater hydro schemes where tunnels are often used to give a strong and directed head of water, sometimes over long distances.

Marine currents generally flow from west to east in the southern hemisphere, which means, for example, that some Pacific species are common on both sides of the tip of South America, but Atlantic species are far less common on the Pacific side. Current generally flow across the Tasman around NZ, meaning that Tasman species are found in the Gulf, but the reverse is less common. In the NZ context there are additional concerns from Maori around mixing water catchments. Given that there has been portage between the two harbours and ships have discharged foreign species from their ballast for generations, there is an argument to say that whatever damage that might be caused by water flow has already occurred and is irreversible.

Nevertheless, the effort to gain consents would be huge and similar initiatives such as hydro between lakes in the deep south of NZ have yet --- or may never --- be developed.

The benefits of linking the Manukau Harbour and Hauraki Gulf may be limited. We can calculate the potential power output based on the water level difference between the two harbours (maximum four metres which is very small in hydro terms), and estimate the costs of a large diameter tunnel between the two harbours: the project is unlikely to be economically viable.

Soft mud and shale are difficult to tunnel, so another factor is the geology of the route. Assuming the intakes/outtakes would need to be several kilometres from the shore, there would be considerable flexibility about the tunnel route rather than being limited to the traditional portage routes across the Auckland isthmus.

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How do tides work?

Tides are generated by the rotation of the earth within the gravitation fields of the moon and sun. Tides change each day in two main patterns:

  • A half-day cycle: due to the rotation of the earth within the gravitational field of the moon, resulting in a period of 12 hours 25 minutes between successive high tides
  • A 14-day cycle: resulting from alignment of the gravitational fields of the moon and sun. At new moon and full moon, the sun’s gravitational field reinforces that of the moon, resulting in the maximum difference between high and low tide, known as spring tides. At quarter phases of the moon, the sun’s attraction partially cancels that of the moon, resulting in minimum or neap tides. The range of a spring tide is typically about twice that of a neap tide.

The incoming, rising tide is the flood tide. The outgoing, falling tide is the ebb tide. The point halfway between high water and low water usually corresponds to the highest current velocity. The current is negligible at slack water.

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What are the differences between the July 2006 and July 2007 RMA applications?

In summary, the main sea floor cabling is reduced from 33 to 7 kilometres, the clearance above the turbines is increased from 5 to 7 meters, and the area covered by the turbines reduced from 1,300 to 300 hectares. Old applications relating to the east-west 30 kilometres cable route terminating at the Hoteo River, and the proposed substation in Rodney, were withdrawn and replaced by an application to terminate the submarine cable at the Pouto Point on North Head. In addition the project is now staged with detailed monitoring at each stage.

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