Binary Power Plants in New Zealand

Greg Bignall & John Burnell
JOGMEC-GNS Workshop, Tokyo
2 June 2016

GNS ScienceOutline• Situation in NZ• Ngatamariki• Ngawha• Discussion

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GNS ScienceSituation in NZ

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GNS Science

Binary Power Turbines in New Zealand• Fields operating with only binary plants– Mokai, Ngatamariki, Ngawha, Tauhara• Binary plants alongside steam turbines– Rotokawa, Wairakei, Kawerau

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GNS ScienceMokaiSlide 5GNS ScienceMokai• Staged development by Maori Land Trust• Combined Cycle technology– Back pressure steam turbine and binary plant• Initial 60 MWe development• Currently 110 MWe• Best option for the reservoir may have been asteam turbine• Choice has added complexity to managing thereservoir• Modular design has benefits
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GNS ScienceTauhara• 25 MWe development originally planned forspecific use• Binary plant was the best option for this stage• Reservoir would support steam turbine– 250 MWe development has been planned– Currently stalled due to low electricity demand in NZ

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GNS Science

Steam Turbines Alongside Binary Plants• Wairakei– 14 MWe binary plant added to utilise energy fromseparated brine• Kawerau– 3 small scale units used by local operators– 14 MWe in total• Rotokawa– Staged development was planned– A small scale initial stage development– 35 MWe binary plant was most suitable
Slide 8GNS ScienceNgatamariki

Slide 9GNS ScienceNgatamariki Resource• Recent development• Exploration of the reservoir occurred in 2004-9• High temperature resource > 285 C• Liquid dominated• Extensive cap• Localised connection to surface

Slide 10GNS ScienceLocation

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GNS ScienceResource Boundary

Boseley et al, 2010
Slide 12GNS ScienceReservoir Temperatures

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GNS Science

Conceptual ModelBurnell, 2010

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GNS ScienceReservoir Modelling

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GNS ScienceMatch to Measured Temperatures

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GNS ScienceMatch to Discharge Test

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GNS ScienceDevelopment Scenarios• Model was used to assess different development
options• For steam turbine (75% injection) downflows
into the reservoir were predicted

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GNS ScienceProject History• Based on modelling predictions a decision wasmade to design for 100% reinjection• Resulted in minimising the impact on theenvironment• From this decision, the only viable technology
was a binary plant• Impacted project economics– More competition around steam turbines• Viable economics over the lifespan of project

Slide 19GNS ScienceProject Design• 100 MWe power station• Largest all binary single-site plant• Four 25 MWe Ormat Energy Converters• 3 deep producing wells• 100% cooled geothermal fluid is reinjected• 4 reinjection wells around periphery of field– Deep wells – 3000m– Located to reduce cooling of production wells• Injection wells thermally stimulated• Operating since 2013 with > 96% availability
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GNS ScienceNgawhaSlide 21

GNS ScienceDevelopment History• Developed by a community owned trust• Developed in stages– 10 MWe– 15 MWe– Proposed 50 MWe expansion• Lower enthalpy resource• Staged approach to assess potential of reservoir• Size of the stages meant binary plant waspreferred option• 100% injection was used
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GNS ScienceDevelopment History II• For the second stage – 15 MWe – there werecommunity concerns about impact on thesprings• Reservoir modelling showed that the springflows were sensitive to reservoir pressure• Even though 100% injection was being injected
there were:– losses due to gas loss and spillage– pressure drop due to density effect of cold injection

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GNS ScienceDevelopment History III• This resulted in a plan to add supplemental
injection• Historical declines had been small– About 0.1 Mpa• Needed to avoid future decreases in pressure• A trial was conducted which demonstrated thatpressures could be changed throughsupplemental injection• Permission was granted to proceed with second
stage
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GNS ScienceDevelopment History IV• Second stage commenced in 2008
• No clear impact on surface features– Some changes observed, but significant naturalvariation• A further expansion has been planned– To a total of 75 MWe• Conditions imposed on the development– Must maintain reservoir pressure to within 0.1 MPaof 2008 levels– No effect on the characteristics of springs
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GNS ScienceDiscussion

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GNS Science

Use of Binary Plants in New Zealand• Major use is for small-scale or staged
developments– Project economics are important– Adds flexibility due to modularity• Can also be driven by need to minimise theimpact on the reservoir or the surface features– 100% reinjection• Projects have all been successful and resulted
in expansions from initial stages• Ngatamariki, Ngawha, Mokai, Tauhara,Rotokawa, Kawerau
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GNS Science

Use of Binary Plants II• Staged developments:––––

Initial stage with a small-medium binary plant
Assess reservoir performance
Add expansion
Reduced risk

• Can also complement a steam turbine– Utilise heat in separated geothermal brine– Will result in cooler reinjection fluid– Depends on reinjection strategy

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GNS Science