By AGILE Consulting Engineers, Solar PV and Battery Energy Storage Systems (BESS) specialists.
Ask five developers how long detailed design takes for a solar or Battery Energy Storage System (BESS) project and you will get five different answers, and all of them can be correct. The honest answer is that detailed design duration is a function of project scale, site complexity, and how quickly external parties respond, not a fixed number on a Gantt chart. Anyone quoting a single figure without qualifying it is either simplifying for a sales conversation or has not delivered enough projects to know better.
Table of Contents
- What Detailed Design Actually Covers
- Typical Timeline Ranges, With Caveats
- Project Scale and Site Complexity
- DNSP Responsiveness and Grid Studies
- How Permitting Interacts With Design Timelines
- Multidisciplinary Coordination
- Compressing the Timeline Without Cutting Corners
- What to Do Next
- FAQ
What Detailed Design Actually Covers
Detailed design sits between the concept or feasibility stage and construction. It is the phase where a single line diagram becomes a fully documented, buildable, and financeable package. For a solar and BESS project that typically includes electrical design (protection studies, cable schedules, earthing design, switchgear specifications), structural design (racking, foundations, battery enclosure support), civil design (site layout, drainage, access roads, cut and fill), and increasingly a control and monitoring package covering the Supervisory Control and Data Acquisition (SCADA) architecture and control philosophy. Each of these disciplines has its own internal review cycle, and they all have to reconcile with each other before the package is issued for construction.
Because detailed design produces the documents that a contractor prices and builds from, its duration is rarely dictated purely by drafting effort. It is dictated by how many iterations are needed to close out grid connection requirements, geotechnical findings, and client design decisions, and how many of those inputs are available before design work starts in earnest.
Typical Timeline Ranges, With Caveats
Industry commentary on PV and BESS delivery generally describes the detailed design phase itself, once key inputs such as geotechnical data, grid connection offer terms, and equipment selection are settled, as running from a few weeks for a small or straightforward commercial system up to several months for a complex utility-scale plant with multiple disciplines and staged issue-for-construction packages. That is a genuinely wide range, and it should be treated as indicative rather than a promise. The detailed design phase is also only one part of a much longer development sequence. Broader industry sources tracking utility-scale BESS development in Australia describe the total journey from concept through to commissioning as commonly spanning several years, shaped heavily by the state planning pathway and the complexity of the grid connection process.
We are deliberately not putting a single number on this for your project, because doing so without knowing your site, your network connection point, and your approval pathway would be guesswork dressed up as precision. What we can say is that the range is genuinely wide, and the variables below are usually what separates the fast end of that range from the slow end.
Project Scale and Site Complexity
A rooftop or small ground-mount commercial system with a straightforward site and a single electrical discipline will move through detailed design markedly faster than a utility-scale plant that combines solar PV, a BESS, and a new or upgraded substation. Scale multiplies the number of documents, the number of internal review gates, and the number of external parties who need to sign off. Site complexity compounds this further. Difficult terrain, contaminated land, flood-prone areas, heritage or environmental constraints, or a footprint that has to be staged around existing infrastructure all add design iterations that a clean greenfield site would not require. Projects that combine PV and BESS on the same site also need the electrical protection studies, thermal management design, and fire safety documentation to be coordinated across both technologies rather than treated as separate exercises, which adds real coordination time even when each individual discipline is otherwise straightforward.
DNSP Responsiveness and Grid Studies
The Distribution Network Service Provider (DNSP), the regulated entity that owns and operates the local electricity distribution network, is one of the biggest sources of schedule variability in detailed design. Design cannot be finalised until the connection offer, network impact study outcomes, and any protection or power quality requirements from the DNSP are known, because these directly shape the electrical design, the switchgear specification, and sometimes the site layout. Industry guidance on grid connection processes in Australia notes that timelines vary materially depending on system size, export capacity, and the complexity of the technical studies involved, and that connection processes for larger or transmission-connected projects have historically run considerably longer than for small embedded systems. When a DNSP or, for larger transmission-connected projects, the relevant network operator takes longer than expected to issue studies or respond to queries, detailed design effectively pauses or proceeds on provisional assumptions that carry rework risk. Building realistic contingency around this interface, rather than assuming a best-case response time, is one of the most reliable ways to protect an overall project schedule.
How Permitting Interacts With Design Timelines
Detailed design and planning approval are not strictly sequential in practice, even though it is tempting to think of them that way. Councils and state planning authorities typically want a reasonably developed design, including site layout, drainage strategy, and sometimes preliminary structural details, before they will assess a development application, yet the final design is often refined after conditions of approval are issued. This creates a genuine chicken and egg dynamic that experienced design teams manage by sequencing the design program around known approval milestones, issuing design-for-planning packages ahead of full issue-for-construction documentation. We cover the planning and council approval landscape in more detail in a companion article on permitting documentation requirements, but the short version is that approval timeframes vary significantly by state and local government area, and that variability flows directly into how detailed design has to be staged.
Multidisciplinary Coordination
A solar and BESS design package only works if the electrical, structural, and civil disciplines are talking to each other continuously rather than working in silos and reconciling at the end. Battery enclosure foundations depend on structural and geotechnical input, cable routing depends on civil layout and trenching design, and protection settings depend on the final equipment selection. When these disciplines are coordinated under one internal review process, clashes get caught early. When they are handled by disconnected teams or bolted together late, the rework and re-issue cycles that follow are one of the most common reasons a detailed design program blows out well past its original estimate.
Compressing the Timeline Without Cutting Corners
There are legitimate ways to shorten a detailed design program, and they generally come down to reducing the number of open variables before design work starts. Locking in equipment selection early, commissioning geotechnical and survey work in parallel with early design rather than waiting for it sequentially, engaging with the DNSP as early as the connection application allows, and running planning and technical design as a coordinated program rather than two separate workstreams all genuinely help. What does not help, and what we would caution against, is compressing internal review cycles or skipping design verification steps to hit an arbitrary date. A design package that has to be reworked after issue for construction almost always costs more time overall than a realistic program would have taken in the first place.
What to Do Next
If you are trying to work out a realistic detailed design program for your project, the most useful starting point is an experienced team that can assess your specific site, connection pathway, and approval requirements rather than apply a generic timeline. AGILE’s solar and BESS system design service works across the electrical, structural, and civil disciplines needed to take a project from concept through to a construction-ready package, and can help you understand where your project sits within the ranges discussed above before you commit to a delivery date.
FAQ
Is there a standard detailed design timeline for every solar BESS project?
No. Duration depends on project scale, site complexity, DNSP responsiveness, and the approval pathway, so any figure quoted without knowing those specifics should be treated as a rough indication only.
Does detailed design happen before or after planning approval?
In practice the two run in parallel to a degree, with a design-for-planning package typically developed ahead of full construction documentation, since most authorities want to see a reasonably developed design before assessing an application.
What usually causes detailed design programs to blow out?
Slow DNSP responses to connection studies, late or incomplete geotechnical data, poor coordination between electrical, structural, and civil disciplines, and late changes to equipment selection are the most common causes.
Can detailed design be rushed to meet a fixed deadline?
It can be compressed by resolving input variables earlier and running workstreams in parallel, but skipping internal review or verification steps to save time usually creates rework that costs more time than it saves.
Does a bigger project always mean a longer detailed design phase?
Generally yes, because scale increases the number of documents, review gates, and external approvals required, though site complexity can make a smaller project take longer than a larger but straightforward one.
Who typically causes the longest delays in the detailed design phase?
Network-related interfaces, particularly DNSP connection studies and protection requirements, are commonly cited as one of the largest sources of schedule variability because design cannot be finalised until connection terms are confirmed.
