By AGILE Consulting Engineers, Solar PV and Battery Energy Storage Systems (BESS) specialists.
A concept layout with a nice render and an indicative yield figure is not a buildable project, it is a proposal. The distance between that proposal and something a contractor can price, procure and build is covered by an engineering phase called detailed design, and it is where the bulk of the technical hours on a solar or battery energy storage system (BESS) project actually land. Developers who underestimate this phase tend to find out the hard way, usually at tender, when quotes come back wildly inconsistent because the drawings were never precise enough to price against.
Table of Contents
- Detailed Design Defined
- Where Detailed Design Sits in the Project Lifecycle
- What Detailed Design Actually Produces
- Electrical Design Deliverables
- Structural and Civil Design Deliverables
- Why Detailed Design Is Not the Same as Concept Design
- Who Uses the Detailed Design Package
- What to Do Next
- FAQ
Detailed Design Defined
Detailed design is the engineering phase that converts a proven concept into construction ready documentation. By this stage a project has usually cleared feasibility, secured a site with reasonable land tenure, and has an indicative grid connection position with the relevant Distribution Network Service Provider (DNSP), the entity that owns and operates the local electricity distribution network. What detailed design adds is precision. Instead of an indicative single line showing block sizes and a nominal capacity, you get a fully coordinated set of electrical, structural and civil drawings, specifications and schedules that a builder can actually take to site and construct from without guessing at intent.
For a solar or BESS asset, this phase typically runs in parallel across three engineering disciplines. Electrical engineers finalise the power system architecture, protection philosophy and cabling. Structural engineers finalise the racking, foundation and container support design. Civil engineers finalise the site earthworks, drainage, access roads and underground services coordination. None of these disciplines can finish in isolation, because a change in cable routing affects trenching, and a change in foundation type affects both structural loading and civil works. Detailed design is as much about coordinating these interfaces as it is about producing individual drawings.
Where Detailed Design Sits in the Project Lifecycle
Most solar and BESS projects in Australia move through a recognisable sequence: concept or feasibility design, preliminary design, detailed design, and then issue for construction (IFC) documentation, the final drawing set stamped as ready for the builder to execute. Concept design answers whether a project is plausible at all, working from a desktop yield estimate, an indicative layout and a rough capital cost. Preliminary design firms up the major equipment selection and grid connection approach enough to support a development application and an early cost plan. Detailed design is where the project stops being theoretical.
This phase usually begins once a project has reasonable certainty on land, planning approval pathway and connection offer terms, because redesigning a fully detailed electrical system after a DNSP changes a connection condition is expensive and slow. Timing detailed design too early risks abortive work. Timing it too late risks delaying financial close or construction mobilisation. Getting that sequencing right is itself a judgement call that an experienced design consultant will flag early in a project’s development.
What Detailed Design Actually Produces
The tangible output of detailed design is a coordinated drawing and document package, not a single report. For a typical utility-scale solar or BESS project this includes a Bill of Quantities (BOQ), an itemised schedule of materials, equipment and quantities used for procurement and construction pricing, alongside equipment general arrangement drawings, technical specifications for major plant, and a construction methodology that ties the disciplines together. The package is written so that a contractor can competitively tender against it with confidence that what they price is what gets built, and so that a DNSP or the Australian Energy Market Operator (AEMO), which operates the National Electricity Market (NEM) and oversees generator connection requirements, can review it against the agreed connection conditions.
Detailed design also produces the supervisory control and data acquisition (SCADA) architecture at a system level, defining how the plant will be monitored and controlled once operating, and how it will report to the network operator. This is conceptual and architectural at the detailed design stage. Vendor specific configuration of the SCADA platform typically happens later, during construction and commissioning, once equipment contracts are awarded.
Electrical Design Deliverables
The electrical package is usually the largest single component of a detailed design set. At its core is the single line diagram (SLD), the master schematic showing how power flows from the PV array or battery through inverters or a power conversion system (PCS), the equipment that converts DC power to grid-compliant AC and manages charge and discharge for a BESS, through transformers and switchgear to the point of common coupling with the network. Around the SLD sits a family of supporting documents: cable schedules setting out conductor sizing and routing, earthing and grounding layout drawings, protection philosophy documentation describing how faults are detected and isolated, and equipment specifications for inverters, transformers, switchgear and, for a BESS, the battery containers themselves.
These drawings are deliberately conceptual in how they are written up for a public audience. The underlying calculations, protection coordination studies and detailed settings are technical, proprietary engineering work carried out for the specific project, not something that belongs in a general explainer. What matters for a developer to understand is that this suite of drawings is what a DNSP reviews for connection compliance, and what a contractor prices and builds from.
Structural and Civil Design Deliverables
Structural design at this stage finalises the racking or tracker system, its foundation type, and the load cases it has been designed against, informed by wind loading assessed with reference to Australian wind actions standards and site-specific geotechnical information. Civil design finalises site earthworks, internal access roads capable of carrying construction and maintenance vehicles, drainage strategy, and the underground reticulation of cable trenches and ducting. For a BESS project, civil and structural design also cover the container or building foundations, bunding or containment where relevant, and access for fire and emergency services.
As with the electrical package, these drawings are produced to a level that supports accurate construction pricing and DNSP or planning authority review, without functioning as a substitute for a qualified structural or geotechnical engineer’s project-specific calculations.
Why Detailed Design Is Not the Same as Concept Design
It is worth being blunt about a common confusion in the market. A concept design, sometimes dressed up with polished renders and an optimistic yield number, is not the same document as a detailed design package, even though both get called “the design” informally. Concept design answers whether a project idea holds together. Detailed design answers exactly how it gets built, by whom, with what materials, and at what verified cost. Tendering a project on concept-level drawings is one of the more common causes of budget blowouts in the sector, because contractors are forced to price assumptions rather than a defined scope, and those assumptions rarely land in the developer’s favour.
The practical test is simple. If a document tells you roughly what a project will look like, it is concept or preliminary design. If a document tells a contractor exactly what to build, in what sequence, to what specification, it is detailed design.
Who Uses the Detailed Design Package
The detailed design package has several audiences, and it needs to satisfy all of them simultaneously. Contractors use it to tender and then construct. Financiers and their independent engineers use it to validate that the project has been designed to a bankable standard before releasing funds. The DNSP and, where applicable, AEMO use relevant sections to confirm the project meets connection and performance requirements. Planning authorities use the civil and structural components to confirm consistency with development approval conditions. Owners and asset managers eventually inherit the package as the basis of their operations and maintenance documentation.
Because so many parties rely on the same document set for different purposes, internal coordination between electrical, structural and civil disciplines during detailed design is not a nicety, it is what determines whether the project is buildable on the numbers everyone has already agreed to.
What to Do Next
If your project is approaching the point where concept drawings need to become something a contractor can actually build from, it is worth having an experienced design team review where the gaps are before they show up in tender responses. AGILE Consulting Engineers works through this transition regularly on Australian solar and BESS projects, and a conversation with the team via AGILE’s solar and BESS system design service is a reasonable place to start if you are scoping detailed design for an upcoming project.
FAQ
What is the difference between detailed design and preliminary design?
Preliminary design firms up major equipment selection and system architecture enough to support planning approval and an early cost plan, while detailed design produces the fully coordinated, construction-ready drawings, specifications and BOQ that a contractor can tender and build from.
How long does detailed design typically take for a utility-scale solar or BESS project?
Duration depends heavily on project size, site complexity and how settled the grid connection conditions are, since electrical, structural and civil disciplines need to coordinate throughout rather than work in isolation.
Does detailed design happen before or after a grid connection offer is finalised?
It generally starts once connection conditions have reasonable certainty, because redesigning a finalised electrical system after a DNSP changes a connection requirement is costly and slows the project down.
Who reviews the detailed design package before construction?
Typically the contractor pricing the works, the project’s financiers or their independent engineer, the DNSP and where relevant AEMO for connection compliance, and the planning authority for consistency with approval conditions.
Can a project go to tender on concept design drawings instead of detailed design?
It can, but contractors are then pricing assumptions rather than a defined scope, which is a common source of inconsistent quotes and budget blowouts once construction pricing is finalised.
Does detailed design include SCADA configuration?
Detailed design typically defines the SCADA architecture and monitoring intent at a system level, with vendor-specific configuration of the platform usually carried out later during construction and commissioning.
