Service
Off-Grid Solar System Design, Gold Coast and South-East Queensland
Stand-alone power system design for properties without grid connection, or properties where the grid connection is available but the homeowner wants independence from it. Load profile analysis, sizing calculations for the solar array and battery bank, hardware specification across the major Australian SPS-capable brands, integration design, and project management of the SAA-accredited installer who delivers the final install. You get one engineer, one written design, and one project manager from the audit through to commissioning.
Who actually needs an off-grid system
Off-grid is the right answer for a specific set of situations and the wrong answer for most others. The four scenarios where it justifies the cost:
- Your property has no existing grid connection and the connection quote from Energex or Essential Energy is over $30,000
- You're building a rural cabin, granny flat, or workshop where running a sub-feed from the main house is uneconomic or impractical
- You have grid available but specifically want full independence (lifestyle preference, frequent grid outages, ideological reasons, or both)
- You're upgrading an existing off-grid system that's at end of life or never worked properly
If your property has a working grid connection and you only want backup capability during outages, you don't want off-grid. You want a hybrid grid-tied system with battery backup. That's a different design and a smaller budget. The audit covers both options and tells you honestly which one fits your situation.
What the System Audit covers for off-grid design
Off-grid design is scoped from a System Audit, $450 residential, with additional time billed at standard rates if the property is rural, the access is significant, or the design complexity warrants it. 2 to 3 hours on site minimum, plus follow-up design time off-site. Here's what we measure:
1. Property characteristics
Site orientation, available roof or ground-mount area, shading from trees and structures across the day and across seasons, distance from buildings (matters for cable runs and voltage drop), and physical access for installation crews and large hardware deliveries. Some rural properties need helicopter access for hardware. Most don't, but it matters to know.
2. Load profile and consumption analysis
What you actually run, when you run it, peak draw, daily energy consumption in kilowatt-hours. We work through every appliance and habitual load: fridges, freezers, hot water (electric or gas), cooking (induction, electric, gas), space heating and cooling, lighting, water pumps, computers, EV charging if applicable. Off-grid systems are sized to consumption, not to roof area. Undersize the bank by 20% and the lights start dimming in winter. Oversize the array by 50% and you've spent $15k more than you needed.
3. Existing electrical state
Switchboard layout, circuit count, AS/NZS 3000 compliance, RCD coverage, and whether the existing electrical can take the new SPS as-is or needs modification. Off-grid installs often involve circuit changes: separating critical loads onto a dedicated essential circuits panel that can run from battery during low-solar periods, while non-critical loads (pool pumps, hot water) only run when the array is producing surplus.
4. Backup generator considerations
Most well-designed off-grid systems include a backup generator for the worst case (extended cloudy weather, unusual loads, system fault). Diesel, petrol, or LPG. Manual start, auto-start, or grid-form integration. The audit covers whether you already have a generator, whether you want one, and how it integrates with the SPS controller.
5. Water and pump loads
Off-grid rural properties usually have rainwater tanks, bore pumps, septic pumps. These are big loads that run intermittently and have to be accounted for in the system sizing. Pump start-up surge in particular can trip an undersized inverter. The design has to handle the worst-case start, not just the running load.
6. Future expansion
Whether you might add an EV in the next five years, expand the house, add a workshop, or run a cabin from the same system. Off-grid systems are easier to design for future expansion than to retrofit later, but only if the question gets asked at design time.
The audit produces a written design document with photos, load analysis, hardware specification options, indicative pricing across the major brands, and a project plan covering both the design phase and the SAA-accredited installation phase. Fee credits 50 percent against installation when you proceed within 90 days.
What audits typically uncover
Off-grid audits surface predictable patterns. Four most common findings.
1. The load assumption is wrong by 30–50%
Most homeowners under-estimate their consumption when they sketch out an off-grid system at the kitchen table. The fridge runs more than they think. The hot water pulls more than they realise. The home office gear is on 24/7. The audit's load profile work usually finds 30–50% more daily consumption than the homeowner expected, which significantly changes battery sizing.
2. The grid connection is cheaper than the off-grid system
For properties within reasonable distance of an existing grid line, the connection quote often comes in at $20–40k. A comparable off-grid system that delivers the same reliability is typically $80–150k installed. Grid-tied with battery backup is typically $40–80k. We're honest when the math doesn't favour off-grid. Sometimes the audit's most valuable finding is "you don't actually need this."
3. The roof isn't where the array should go
Many rural properties have plenty of ground space and the optimal array location is a ground-mount frame in a clear, north-facing area, not the house roof. Ground-mount arrays are easier to clean, easier to service, easier to expand, and often produce more because they're not shaded by trees. The audit considers ground-mount as the default for rural sites and only goes roof-mount when ground-mount isn't practical.
4. The existing electrical needs work before the SPS goes in
Older rural houses often have switchboards that pre-date current standards, no RCD protection, and circuit layouts that don't separate critical from non-critical loads. The off-grid install is the right time to fix this, not after. The audit identifies the electrical work that should happen as part of the SPS project rather than as a separate later job.
What an off-grid project actually involves
Off-grid projects are bigger than typical residential work and run across two distinct phases: design and install. Each has its own deliverables and timeline.
Phase 1: Design
Two to three weeks from audit to written design document. Includes load analysis, system sizing calculations, hardware specification (with three brand options ranked), single-line electrical diagram, civil and structural notes for ground-mount or roof-mount arrays, generator integration plan, and a project budget. The design document is yours regardless of who you use for the install. Indicative design fee $2,500 to $6,000 depending on system complexity, deducted from total project cost if you proceed.
Phase 2: SAA-accredited installation
Five to ten days on site for the install crew. Until Iron and Air's SAA-SPS accreditation issues, this phase is delivered through an SAA-accredited partner installer working to our design. We project-manage the partner, you have one point of contact (us), and the deliverables are documented and warranted as a single integrated project. Indicative install cost varies enormously by system size: a small cabin SPS runs $30–50k, a full residential system runs $60–150k, larger or remote-access systems can run higher.
Phase 3: Commissioning and handover
Two days on-site, plus one to two weeks of operational monitoring before handover sign-off. Includes commissioning every component, confirming charge profiles match the bank chemistry, configuring the system controller (Cerbo GX, Selectronic SP-PRO controller, or whatever the design specified), setting up VRM or equivalent remote monitoring, and a half-day training session for the homeowner on daily use, troubleshooting, and what each fault code means.
Once Iron and Air's SAA-SPS accreditation issues, the partner-installer step disappears and we deliver everything directly. Until then, the design and project-management work is genuinely better with the partner arrangement than without: you get one engineer focused on the design and integration, and a specialist crew focused on the SAA install, rather than one party trying to do both.
Available packages
Home System Audit, from $450 (Zone 1)
2 to 3 hours on site for residential properties within Zone 1. Site assessment, initial load profile conversation, written report, and quoted design fee for the next phase.
Larger or rural site audits
Properties outside Zone 1, larger sites, or sites with significant access requirements quoted case-by-case. Typical range $600 to $1,800 depending on travel and complexity.
Final design and installation costs land after the audit. Audit findings credit 50 percent against installation when you proceed within 90 days. See /pricing/ for the full pricing structure.
What every off-grid prospect should understand
Off-grid solar isn't grid-tied solar with a battery added on. It's a fundamentally different system architecture, and the design decisions matter more than they do on a grid-tied install. Here's the technical context most prospects don't get from a brochure.
Battery sizing is more important than array sizing
Grid-tied systems can over-export to the grid when production exceeds use, and pull from the grid when consumption exceeds production. Off-grid systems can do neither. The bank is the only buffer, which means it has to be sized for autonomy: typically two to three days of consumption with no solar input, accounting for cloudy weather and seasonal variation. Undersize the bank and the system fails when the weather turns. Oversize the bank and you've spent $20–40k of unnecessary capacity.
LiFePO4 is the right chemistry for off-grid, almost always
Lead-acid (AGM, gel, flooded) was the off-grid standard for decades and still works, but LiFePO4 is now the right choice for nearly every new install. Three reasons: 80% usable depth-of-discharge versus 50% for lead-acid (effectively halves the bank cost per usable kilowatt-hour), 3000–5000+ cycles versus 500–1500 (doubles the bank life), and constant voltage under load (lights don't dim as the bank discharges). The price premium has narrowed dramatically since 2020 and the lifecycle cost favours LiFePO4 in nearly every case.
The major Australian SPS-capable brands
Selectronic (Australian-made, extremely reliable, expensive, smaller ecosystem), Victron (excellent ecosystem, strong VRM remote monitoring, well-supported in Australia, mid-pricing), Sigenergy (newer, growing rapidly, integrated battery and inverter, good value), Schneider XW (American, robust, less common locally), and Sungrow (newer SPS offerings, good value, some integration limitations). Each has strengths. The audit picks the right brand for your specific design constraints rather than defaulting to a single answer.
Generator integration is more important than it sounds
A well-designed off-grid system runs fine on solar 90–95% of the year. The remaining 5–10% (extended cloudy periods, unusual loads, system service work) is where the generator earns its keep. Most well-designed systems include auto-start generator integration where the system controller starts the generator when battery SOC drops below a threshold and stops it when SOC reaches a target. This means you never come home to a flat bank, ever. Without auto-start, a week of bad weather while you're away can leave the system unrecoverable until you arrive to manually start the generator.
SAA accreditation matters here, specifically
Stand-alone Power Systems are one of the SAA accreditation classes alongside Grid-Connected Photovoltaic and Grid-Connected Battery Storage. SAA-SPS accreditation is required for the installer to claim Small-scale Technology Certificates (STCs), which is the federal solar rebate worth $3,000 to $8,000 on a typical SPS install depending on system size. Without an SAA-SPS accredited installer, you can't claim the STCs and you may not be eligible for state-level rebates either. Iron and Air's SAA-SPS accreditation is in process. Until it issues, the SPS install component of every project is delivered by an SAA-SPS accredited partner installer working to our design, so STCs are claimable in full.
For deeper reading, see our guides on SAA Accreditation Explained, Off-Grid System Design, and Battery Chemistry.
Frequently asked
▸ Can I really run a whole house off-grid in South-East Queensland?
▸ What does a typical off-grid system cost?
▸ How does the SAA partner installer arrangement work in practice?
▸ Will I lose access to the STC rebate?
▸ What happens when your SAA accreditation issues?
▸ Can I add to it later if my consumption grows?
▸ Do I need an electrical certificate to live in the property without grid?
▸ What if I want to go on the grid later?
▸ How long does the whole project take from first call to commissioned system?
Book a System Audit
Off-grid projects start with the audit. Three to four hours on site, written design document within two to three weeks, fixed-price project plan covering design and install phases. Most enquiries get a response within four business hours. If you've already got load data (recent power bills, generator runtime logs, or load measurements), bring them. They accelerate the design work significantly.