By AGILE Consulting Engineers, Solar PV and Battery Energy Storage Systems (BESS) specialists.
Most disputes on solar and battery energy storage system (BESS) construction sites trace back to the same root cause: a drawing that was ambiguous where it needed to be precise. The electrical drawing package is the largest and most scrutinised part of a detailed design set, reviewed by contractors pricing the works, by the Distribution Network Service Provider (DNSP) assessing connection compliance, and by financiers confirming the project has been engineered to a bankable standard. Knowing what should actually be in that package is useful whether you are a developer commissioning the work or a stakeholder trying to read it.
Table of Contents
- The Single Line Diagram
- Cable Schedules
- Earthing and Grounding Layout
- Protection Schematics
- Equipment General Arrangements and Layouts
- SCADA and Monitoring Architecture
- Australian Standards Context
- What to Do Next
- FAQ
The Single Line Diagram
The single line diagram (SLD) is the master electrical schematic for the project, and it is usually the first drawing anyone reviewing a system actually opens. It represents the complete power path using simplified single-line notation, from the photovoltaic (PV) array or battery containers through inverters or the power conversion system (PCS), the equipment that converts DC power to grid-compliant AC and, for a BESS, manages charge and discharge, through step-up transformers and switchgear to the point of common coupling with the network. A properly developed SLD shows nominal voltages at each stage, major equipment ratings, circuit breaker and switch positions, and the overall system topology, including how strings, arrays or battery blocks are grouped and combined.
Because the SLD is the drawing most reviewers reach for first, whether that is a contractor’s estimator, the DNSP’s connections team, or a financier’s independent engineer, its accuracy and clarity set the tone for how the rest of the package is trusted. An SLD that is inconsistent with the cable schedule or protection documentation is one of the fastest ways to trigger a round of costly review queries.
Cable Schedules
The cable schedule is the detailed register that sits behind the SLD, listing every significant cable run in the system: conductor type and size, voltage rating, insulation, origin and destination, route, length, and termination details. On a utility-scale solar project this can run to many hundreds of individual circuits once DC string cabling, AC inverter output cabling and medium voltage collector cabling are all accounted for. For a BESS, the schedule also covers inter-rack and inter-container cabling and the connections back to the PCS.
Cable sizing itself is a piece of specific engineering calculation, accounting for current carrying capacity, voltage drop over distance, and derating for installation method and ambient conditions, carried out against the requirements of the Wiring Rules and relevant photovoltaic and battery installation standards. That calculation work is project-specific and is not something a general article should attempt to teach as a how-to. What matters for a developer to understand is that the cable schedule, once finalised, becomes a key input to both the BOQ, the Bill of Quantities used for procurement and construction pricing, and to construction sequencing on site.
Earthing and Grounding Layout
The earthing and grounding layout shows how every metallic component in the system, PV array frames, inverter and transformer enclosures, battery container structures, switchgear housings and fencing, connects back to the site’s earthing grid. This is one of the drawings that gets particular attention during DNSP and electrical safety review, because an incomplete or poorly coordinated earthing design is a genuine safety risk, not just a compliance formality.
At detailed design stage, the earthing layout is developed with reference to site-specific soil resistivity data where available, since soil conditions materially affect how an earthing grid needs to be configured to achieve safe touch and step voltages across the site. This is deliberately kept at a design-intent level in public-facing material. The underlying earthing calculations and grid design are technical work performed for the specific site and are not published as a how-to guide, both because they are project-specific and because getting this wrong has real safety consequences.
Protection Schematics
Protection schematics describe, at a conceptual level, how the system detects and isolates electrical faults, covering the philosophy for protecting inverters, transformers, medium voltage feeders and the connection to the network. The intent is to ensure faults are cleared quickly and selectively, so that a fault in one part of the plant does not force an unnecessary shutdown of the whole system, while also meeting the DNSP’s requirements for how the plant behaves during and after a network disturbance.
Protection coordination studies, relay setting calculations and specific device configurations are specialist engineering deliverables prepared for the actual project and its specific equipment. They are not the kind of content that belongs in a general explainer, both because the detail is proprietary to the specific design and because protection settings genuinely need to be engineered and verified by a qualified protection engineer rather than approximated from a blog post.
Equipment General Arrangements and Layouts
Alongside the schematic drawings, the electrical package includes general arrangement drawings showing the physical layout of major equipment: inverter and PCS skid positions, transformer pads, switchroom and control building layouts, and the overall site electrical layout showing how trenching and cable routes connect everything together. These drawings are where the electrical design meets the civil and structural design most directly, since equipment positions determine trenching routes, and trenching routes determine civil earthworks scope.
Coordinating these general arrangements against the structural foundation drawings and the civil site layout is one of the more time-consuming but genuinely valuable parts of detailed design, because clashes caught on paper are vastly cheaper to fix than clashes caught on site.
SCADA and Monitoring Architecture
The electrical package also typically includes a system-level supervisory control and data acquisition (SCADA) architecture drawing, showing how inverters, the PCS, switchgear and metering equipment communicate with the plant control system, and how that system reports to the DNSP and, where applicable, to the Australian Energy Market Operator (AEMO), which operates the National Electricity Market (NEM). At detailed design stage this is architectural rather than fully configured, describing data points, communication pathways and control intent, with vendor-specific configuration typically finalised during construction and commissioning once equipment contracts are in place.
Australian Standards Context
Electrical design for Australian solar and BESS projects is developed with awareness of the relevant Australian and New Zealand Standards framework, including the Wiring Rules that govern general electrical installation practice, the standard covering installation and safety requirements for photovoltaic arrays, the standard covering grid connection of inverter-based energy systems, and the standard specifically covering battery energy storage system installation. These standards interact, and a competent detailed design package is developed with all of them in view rather than treating any one in isolation. Specific clause-level requirements are project and equipment specific, so a design consultant working on your project is the right source for exactly how a given standard applies to your configuration, rather than a generic summary.
What to Do Next
If you are reviewing an electrical drawing package, whether your own or one produced by another consultant, and want a second set of experienced eyes on it before it goes to tender or to the DNSP for review, that is a common and sensible step to take. AGILE Consulting Engineers produces and reviews electrical detailed design packages for Australian solar and BESS projects, and AGILE’s solar and BESS system design service is where that conversation can start.
FAQ
What is the most important drawing in a solar or BESS electrical package?
The single line diagram is generally treated as the master reference, since it sets the overall system topology that every other electrical drawing, including cable schedules and protection documentation, needs to align with.
Why does the cable schedule matter beyond just listing cable sizes?
It becomes a key input to the Bill of Quantities for procurement and to construction sequencing on site, so errors or inconsistencies in the schedule tend to surface as costly issues during the build rather than earlier.
Are protection settings included in the detailed design drawings a developer receives?
The drawings typically show protection philosophy at a conceptual level, while the underlying coordination studies and specific relay settings are specialist engineering work carried out for the project rather than published in general documentation.
Who reviews the earthing and grounding layout before construction?
It is typically reviewed by the DNSP as part of connection assessment and by the project’s own electrical safety review process, given the direct safety implications of an incomplete earthing design.
Does the electrical package include SCADA configuration details?
It typically includes the system-level SCADA architecture and monitoring intent, with vendor-specific configuration usually finalised later during construction and commissioning once equipment is contracted.
Which Australian standards typically apply to solar and BESS electrical design?
Design work is developed with awareness of the Wiring Rules, the standard covering photovoltaic array installation and safety, the standard covering grid connection of inverter-based systems, and the standard covering battery energy storage system installation, applied together rather than in isolation.
