By AGILE Consulting Engineers, Solar PV and Battery Energy Storage Systems (BESS) specialists.
Ask three developers when “design” happens on a solar or battery energy storage system (BESS) project and you will likely get three different answers, because the word gets applied loosely to everything from an early desktop layout to the final issued-for-construction drawing set. Treating these as interchangeable is how projects end up with mismatched budgets and confused contractors. The reality is a staged process, with each gate narrowing uncertainty and raising the cost of getting it wrong.
Table of Contents
- Why a Stage-Gate Process Exists
- Stage One: Concept and Feasibility
- Stage Two: Preliminary Design
- Stage Three: Detailed Design
- Stage Four: Issue for Construction Documentation
- Where Projects Actually Lose Time
- The Australian Grid Connection Overlay
- What to Do Next
- FAQ
Why a Stage-Gate Process Exists
Solar and BESS projects are capital intensive and technically interdependent, so the industry has converged on a staged, gated design process rather than jumping straight to construction drawings. Each stage answers a narrower question than the last, and each gate is a deliberate checkpoint where a developer decides whether to commit further capital before the next round of engineering begins. This matters because detailed engineering is expensive to produce and expensive to redo. Locking in a site, a connection position and a technology selection before detailed design starts protects that investment.
The stages are not rigid boxes with sharp edges in practice. On a real project they overlap, and elements of one stage get revisited when new information arrives, such as a revised connection offer from the Distribution Network Service Provider (DNSP), the entity that owns and operates the local electricity network. But the underlying logic, moving from broad feasibility to narrow construction detail, holds across nearly every Australian project AGILE has been involved with.
Stage One: Concept and Feasibility
Concept and feasibility work answers a blunt question: is this project worth pursuing at all. It typically involves a desktop resource assessment, an indicative layout based on parcel size and constraints, a rough capacity and yield estimate, and an early view of grid connection feasibility, land tenure and planning pathway. For solar, this is often the stage where a preliminary energy yield simulation is run to sanity check annual generation against the proposed capacity.
Structural and civil considerations at this stage are largely desktop-based too, drawing on published soil mapping, flood mapping and available wind region data rather than site-specific investigation. The goal is to screen out projects with fatal flaws early, before spending on the more expensive engineering that follows.
Stage Two: Preliminary Design
Preliminary design firms up enough of the technical picture to support a development application and a more reliable cost plan. Major equipment selections, such as inverter or power conversion system (PCS) topology and nominal transformer capacity, get locked in at an indicative level. The site layout becomes more specific, accounting for real setbacks, easements and known constraints rather than assumptions. Early geotechnical desktop studies or a limited site investigation may occur here to de-risk foundation assumptions before detailed design commits to a specific footing type.
On the grid side, this is usually when a formal connection enquiry is lodged with the DNSP, and in some cases the Australian Energy Market Operator (AEMO), which operates the National Electricity Market (NEM) and is involved in connection processes where the National Electricity Rules require it. The indicative connection response from this enquiry materially shapes what detailed design later has to work with, so getting the enquiry submitted with accurate project data matters more than developers sometimes appreciate.
Stage Three: Detailed Design
Detailed design is where the project stops being conceptual. Electrical, structural and civil disciplines work in parallel to produce a fully coordinated set of drawings, specifications and a Bill of Quantities (BOQ), the itemised schedule of materials and equipment used for procurement and construction pricing. On the electrical side this includes the single line diagram (SLD), the master schematic of the power system, along with cable schedules, earthing layouts and protection philosophy documentation. On the structural and civil side it includes racking or tracker foundation design informed by site-specific geotechnical data and wind loading assessment, plus earthworks, drainage and access road design.
This stage also formalises the supervisory control and data acquisition (SCADA) architecture at a system level, describing how the plant will be monitored and how performance and fault data will be reported, without yet configuring vendor-specific settings, which typically happens during construction and commissioning once contracts are awarded. Detailed design should not begin in earnest until connection conditions and site data have reasonable certainty, because redesigning a coordinated electrical and structural package after a material change is genuinely costly.
Stage Four: Issue for Construction Documentation
Issue for construction (IFC) documentation is the final, contractor-ready version of the detailed design package, incorporating any changes arising from tender clarifications, procurement lead times or value engineering discussions. It is the version stamped and released for the build to actually proceed against, and it is what the construction contract typically references as the scope of works. Any subsequent changes during construction are managed through a formal variation process rather than informal drawing updates, because uncontrolled drawing revisions during a build are how disputes and defects both tend to originate.
For a BESS project specifically, IFC documentation also needs to align with whatever fire safety, emergency response and DNSP protection requirements were settled during detailed design, since these tend to be scrutinised closely during commissioning and energisation approval.
Where Projects Actually Lose Time
In AGILE’s experience, the time lost on solar and BESS projects rarely comes from any single stage running long. It comes from the interfaces between stages, particularly the handover from preliminary design into detailed design when connection conditions are still in flux, or from detailed design into construction when procurement lead times force late substitutions of major equipment. A transformer or PCS substitution made late in the process can ripple back through the electrical protection philosophy and even the civil footprint, which is exactly the kind of rework a well-run detailed design phase is meant to prevent, not cause.
Good practice is to freeze major equipment selections before detailed design starts in earnest, and to treat any later substitution as a formal design change with its own review, rather than a quiet swap on a drawing register.
The Australian Grid Connection Overlay
Australian projects carry an additional layer that developers in some other markets do not deal with to the same degree: the interaction between DNSP connection requirements and AEMO’s oversight of generator performance standards under the National Electricity Rules. AEMO has been working to streamline technical connection requirements for solar, wind and BESS projects connecting to the NEM, which is a reminder that this process is not static and detailed design teams need to stay current on the applicable connection framework for the specific network and jurisdiction involved. This overlay is one of the reasons detailed design timing matters so much in Australia specifically, since a project can be technically ready for detailed design well before its connection position is contractually settled.
What to Do Next
If you are trying to work out where your project actually sits in this sequence, or whether it is ready to move into detailed design, it helps to have that assessed by a team that works across the full stage-gate process day to day. AGILE Consulting Engineers supports Australian developers through each of these stages, and AGILE’s solar and BESS system design service is a reasonable starting point for a conversation about where your project sits and what detailed design will involve.
FAQ
What triggers the move from preliminary design into detailed design?
Reasonable certainty on land tenure, planning pathway and grid connection conditions, since starting detailed design before these are settled risks expensive rework if a DNSP or AEMO connection requirement later changes.
Is issue for construction the same document as detailed design?
Not quite. IFC documentation is the final, stamped version of the detailed design package after tender clarifications and any late procurement changes have been incorporated, and it is what the construction contract references.
Why do BESS projects sometimes need extra design steps compared with solar-only projects?
BESS projects add fire safety, emergency response and containment considerations to the structural and civil scope, alongside protection philosophy work specific to battery charge and discharge behaviour, which solar-only projects do not carry to the same extent.
Can detailed design start before a DNSP connection offer is finalised?
It can begin on the basis of indicative connection conditions from the enquiry stage, but committing fully before those conditions firm up creates rework risk if the final offer differs materially.
What causes the most rework between detailed design and construction?
Late substitution of major equipment, such as transformers or power conversion systems, driven by procurement lead times, which can ripple back through the electrical protection design and civil footprint if not managed as a formal design change.
Does AEMO review every solar and BESS project individually?
AEMO’s involvement depends on the connection pathway and what the National Electricity Rules require for that project’s size and network location, working alongside the relevant DNSP or transmission network service provider.
