Central West Orana REZ
Snapshot
Australia’s first Renewable Energy Zone (REZ), Central West Orana is a roughly 20,000 km² zone in Central West NSW, centred on Dubbo and Dunedoo, that will connect new wind, solar and storage generation to the grid. Its transmission network is the first competitively procured REZ transmission project in the country.
Turnbull Engineering has been involved across the life of the project, providing civil and structural design during the competitive tender phase, and now supporting design management and delivery for the network operator, ACEREZ.
Location
Central West NSW (around Dubbo and Dunedoo)
Network Operation
ACEREZ (ACCIONA, COBRA and Endeavour Energy)
Turnbull’s role
Bid-phase design; current design management and delivery support
Project Value
$5.5 billion (transmission)
Program
2022-2029
Turnbull’s Timeline
Tender from 2022 • in delivery 2025-present (energisation 2028)
Project Overview
The $5.5 billion transmission project will build new high-voltage lines, energy hubs and supporting infrastructure to carry renewable power from the REZ to load centres in Newcastle, Sydney and Wollongong. It comprises around 90 kilometres of 500 kV and 150 kilometres of 330 kV overhead transmission lines, together with an energy hub at Merotherie and switching stations.
The network will unlock at least 4.5 gigawatts of new capacity from 2028, connecting 7.7 gigawatts of wind and solar and powering more than two million homes and is expected to grow towards 6 gigawatts by 2038. EnergyCo appointed ACEREZ, a partnership of ACCIONA, COBRA and Endeavour Energy, to design, build, finance, operate and maintain the network for 35 years, reaching financial close in April 2025. Construction began in June 2025.
Design and delivery scope
Turnbull’s scope across the project has spanned:
Road design
Pavement design
Flood modelling and drainage design
Civil design for transmission towers and substations
Structures (excluding transmission towers)
Public utility impact coordination
Turnbull’s Involvement
Tender phase (from 2022)
During EnergyCo’s competitive procurement, Turnbull provided civil and structural design as part of the CPB and UGL design-and-construct team within one of the shortlisted consortia bidding to deliver the transmission network.
Delivery phase (2025–present)
Following ACEREZ’s appointment, Turnbull was engaged by ACEREZ (ACCIONA) to support design management and delivery broadly across project work that is continuing as construction progresses.
Project Highlights
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Involvement across the project life
From design support during the competitive tender through to current delivery support for the network operator, Turnbull has built deep familiarity with the project across both phases.
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De-risking delivery through design review
Turnbull’s road design reviews, flood modelling review and value engineering helped identify risks early across the network’s road and drainage packages, helping the project avoid certification issues that could otherwise have caused significant construction delays.
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Modelling 21 catchments in eight weeks
During the tender phase, Turnbull built rainfall-on-grid TUFLOW models across 21 rainfall catchments spanning 3,500 km², using Sub-Grid-Sampling and Quadtree techniques to complete in eight weeks work that would typically take weeks per catchment.
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Civil design optimisation
Turnbull’s team rethought the design rather than just delivering it from the construction side: overhauling the substation earthworks and drainage strategy to cut formal underground drainage by more than 50% per bench, while challenging the client's own design criteria on the access roads to justify removing many kilometres of road through deep expertise in flood modelling and flood behaviour, and pushing the designers to switch over 80% of diversion channels (more than 6km) from concrete to rock-lined, delivering significant time and cost savings to the construction team.
By the numbers
21
modelling catchments
8
week turnaround
2022 - ongoing
involved across the life of the project
Client Feedback
"Working on a project like CWOREZ, you quickly figure out who you can rely on when things get complicated. Turnbull Engineering is one of those design teams we can rely on.
They've contributed meaningfully to design management, design change and construction phase services — identifying value engineering opportunities early and actually seeing them through, which in my experience is where most of that work falls over on major projects.
Design works include Merotherie Road re-design and sub-station bench and drainage design which without their efforts, CWOREZ would have faced certification issues with external stakeholders and the Independent certifier which would have resulted in significant construction delays for CWOREZ.
Their understanding of the local regulatory landscape has been a genuine asset, particularly in helping our design partners avoid the usual pitfalls with Australian standards and guidelines.
What I'd highlight most, though, is their professional integrity, it's been noticed across the project, from the client through to our specialist subcontractors. On a multi-disciplinary contract of this scale, that kind of reputation matters.”
Mark Cowan
Senior Project Engineer, Acciona