By AGILE Consulting Engineers, Solar PV and Battery Energy Storage Systems (BESS) specialists.
A Battery Energy Storage System (BESS) does not go from concept to construction in one step, and treating it that way is how projects end up with a design that has to be substantially reworked once real site data and connection feedback arrive. The process runs through several distinct stages, each producing outputs the next stage depends on, and skipping or compressing any of them tends to show up later as delay, not saved time.
Table of Contents
- Starting Point: Concept and Feasibility Inputs
- Preliminary Design and System Sizing
- Site Investigation and Constraints Mapping
- Electrical Design and Single Line Development
- Civil, Structural, and Enclosure Design
- Grid Connection Application and Compliance Package
- Design Review, Issue for Construction, and Handover
- What to Do Next
- FAQ
Starting Point: Concept and Feasibility Inputs
Every BESS design starts from a set of commercial and technical assumptions: an indicative capacity in megawatt hours, a candidate site or connection point, and a rough understanding of what the system needs to achieve, whether that is peak demand management, backup power, wholesale market participation, or Frequency Control Ancillary Services (FCAS) revenue through the National Electricity Market (NEM). These inputs are rarely precise, and part of the design process is progressively testing and refining them as real data becomes available, rather than treating the initial concept as fixed. Feasibility level modelling at this stage, using historical load or generation data where it exists, gives the project a defensible starting point without committing to detailed engineering effort too early.
Preliminary Design and System Sizing
Preliminary design takes the concept and tests it against enough technical detail to confirm the project is viable before significant money is committed: rough sizing of the battery and Power Conversion System (PCS), an indicative site layout, and an early view of the likely connection point and its capacity to accept the system. This stage is deliberately less detailed than what follows, its purpose is to catch fundamental problems, an undersized connection point, an unsuitable site, before detailed engineering effort is spent on a design that cannot proceed. A preliminary enquiry to the relevant DNSP at this point, even an informal one, can save considerable time by flagging capacity constraints before the project team commits to a particular site or configuration.
Site Investigation and Constraints Mapping
Once a site is confirmed, the design process moves into gathering the real constraints that will govern it: geotechnical conditions for foundation design, easements and setbacks, existing services, bushfire or flood overlays, and the specific technical characteristics of the intended connection point, including available fault level and any network capacity limitations. This stage often reshapes elements of the preliminary design, a site with poor geotechnical conditions might change the foundation approach, or a lower than expected fault level might change protection settings, which is exactly why it happens before detailed design is finalised rather than after.
Electrical Design and Single Line Development
Electrical design is where the system’s technical architecture gets fixed: cable sizing, protection coordination, control philosophy, and the single line diagram that represents the entire electrical system on one drawing. This diagram becomes the reference point for everyone downstream, procurement, the electrical contractor, and the DNSP reviewing the connection application, so its accuracy matters enormously. Our guide to single line diagrams covers what a properly developed one for a solar or BESS project needs to show.
Civil, Structural, and Enclosure Design
In parallel with electrical design, civil and structural engineering fixes the physical footing of the project: foundation design for battery enclosures and any associated switchgear or transformer, access and drainage arrangements, and separation distances between the battery system and other structures as required under the applicable battery safety standard. For ground mount systems in particular, this work has to account for wind and seismic loading on enclosures, along with the practicalities of maintenance access over the system’s operating life. Bushfire prone area classifications and flood overlays, where relevant to the site, can also influence enclosure specification and foundation height, and are best identified during the earlier constraints mapping stage rather than discovered here.
Grid Connection Application and Compliance Package
With electrical and civil design settled, the project prepares its formal connection application to the relevant DNSP, or for larger systems, works through AEMO’s generator performance standards process under the National Electricity Rules. This package typically includes fault level studies, protection coordination reports, voltage rise calculations, and, depending on system size, modelling of how the BESS behaves under network disturbance conditions. It is usually the longest single approval step in the entire project timeline, and design quality earlier in the process directly determines how many review cycles it takes.
Design Review, Issue for Construction, and Handover
Before drawings go to a contractor, they typically pass through an internal or independent design review, checking coordination between disciplines and confirming the design still matches the approved connection application. Once cleared, the package is issued for construction, and the design team’s role usually continues through construction support, responding to site queries and reviewing any variations, before final handover and commissioning. Our overview of how a solar and BESS project moves from concept to construction walks through how these stages connect end to end.
What to Do Next
If your project is sitting at the concept or preliminary stage and you want a clearer view of what detailed design will actually involve for your site, it helps to have that conversation before a connection application deadline is looming. AGILE’s BESS engineering service covers the full sequence described here, from early sizing through to construction support, so each stage feeds cleanly into the next.
FAQ
How long does the BESS design process typically take?
It depends heavily on system size and the complexity of the connection point, with grid connection approval usually the longest single stage. Smaller behind the meter systems generally move faster than grid scale projects requiring AEMO involvement.
Can preliminary design and detailed design happen at the same time?
They can overlap in practice, but detailed design decisions made before preliminary design has confirmed site and connection viability carry real risk of rework if fundamental assumptions turn out to be wrong.
Why does the connection application take so long relative to the design work itself?
DNSPs and AEMO have to assess how a new system affects network stability and other connected parties, which involves detailed technical review, not just an administrative check. Complex sites or borderline fault levels lead to further review cycles.
Does the design process differ for grid scale versus commercial BESS projects?
The stages are broadly the same, but grid scale projects carry additional steps, particularly around AEMO’s generator performance standards, that smaller commercial and industrial systems typically do not encounter.
What causes the most rework during BESS design?
Site or connection data discovered late, after detailed design has already progressed, is the most common cause. Thorough site investigation and early DNSP engagement are the main ways to reduce this risk.
