Off-Grid Solar System Calculator (Australia)
Free Australian off-grid solar calculator. Sizes PV array (kW), battery bank (kWh), and inverter (kW) from daily kWh load using BoM irradiance data and CEC-aligned design factors.
Off-Grid Solar System Calculator
How to use this calculator
The Australian off-grid calculator above takes your daily kWh load and BoM-derived peak sun hours and returns three numbers: PV array size in kW DC, battery bank capacity in kWh nameplate, and inverter continuous kW rating. All values are in metric units and align with CEC Off-Grid Design Guidelines.
- Daily energy use (kWh) — your average daily AC load. Pull it from a recent retailer bill (quarterly kWh ÷ 90) or sum nameplate watts × hours-on. The AER’s State of the energy market puts the residential average at 14-18 kWh/day depending on state. Off-grid Australian properties typically run 8-15 kWh/day because high-draw loads (electric oven, instantaneous hot water) get swapped for LPG.
- Peak sun hours (h/day) — annual average solar exposure from the BoM Daily Global Solar Exposure dataset. Typical values: Alice Springs 6.0, Perth 5.5, Brisbane 5.2, Adelaide 5.0, Sydney 4.6, Melbourne 4.2, Hobart 3.7. Default 4.8 covers most of NSW/VIC/SA inland; bump down for Tasmania.
- Days of autonomy — 2 days for mainland temperate; 3-4 days for Tasmania, Victorian alps, South-West WA.
- Battery chemistry — LiFePO₄ (BYD Premium HVS, Pylontech Force-H2, Sungrow SBR, GivEnergy AC, Sonnen) is now standard for new Australian off-grid builds. Tubular gel and AGM lead-acid (Rolls Surrette, Trojan) still appears in Bushlight remote-Indigenous-community installations because of harsh-environment ruggedness.
- Peak instantaneous load (W) — usual Aussie suspects: bore pump 1,500-3,000 W, kettle 2,400 W, microwave 1,100 W, ducted reverse-cycle 4,000-6,000 W. Most Australian off-grid systems run a 5-7.5 kW Selectronic SP PRO continuous.
How the math works
The Australian calculator follows methodology in the CEC’s Stand-alone Power System Design Guidelines and AS/NZS 4509.2 (Stand-alone power systems — System design):
PV array (kW DC):
kW = daily_kWh / (peak_sun_hours × derate)Derate 0.77 covers AS/NZS 4777-compliant inverter losses, MPPT charge-controller losses, DC cable losses (usually generous in Aussie installs because of long DC runs), tropical soiling, and module temperature derating (panels lose 0.35%/°C above 25°C cell temp; mainland summer cell temps hit 60-70°C). With AU defaults of 10 kWh/day at 4.8 PSH: kW = 10 / (4.8 × 0.77) = 2.7 kW DC, typically 6-7× 415 W panels (Trina Vertex S+, Jinko Tiger Neo, Longi Hi-MO).
Battery bank (kWh nameplate):
usable_kWh = daily_kWh × autonomy_days
nameplate_kWh = usable_kWh / (DoD × battery_round_trip_eff)10 kWh × 2 days = 20 kWh usable; nameplate = 20 / (0.90 × 0.95) = 23.4 kWh of LiFePO₄. Maps to about 4× Pylontech US5000 (4.8 kWh each) or 1× BYD HVS 22.0.
Inverter (kW continuous):
kW = peak_load_W × 1.25 / 1000A 3,500 W bore-pump start plus 800 W background = 4,300 W × 1.25 = 5.4 kW. The Selectronic SP PRO 7.5 kW or Victron Quattro 5 kVA are standard answers.
What an off-grid system actually costs in Australia (Q1 2026)
Pulling installed-cost ranges from CEC-accredited specialists (Solar Service Group Brisbane, Bushlight (Centre for Appropriate Technology) NT, Going Off Grid Tas, MC Electrical Brisbane). All prices BEFORE the federal Cheaper Home Batteries Program rebate (≈A$370/kWh) and STC rebate (Zone 3 ≈A$36/STC):
| System size | PV kW | Battery kWh | Total installed | After rebates |
|---|---|---|---|---|
| Cabin / weekender | 2-3 | 12-18 (Li) | A$18,000-25,000 | A$13,500-19,000 |
| Small full-time off-grid (10 kWh/day) | 3-4 | 20-30 (Li) | A$28,000-38,000 | A$21,000-29,000 |
| Full off-grid house (15 kWh/day) | 5-7 | 30-50 (Li) | A$45,000-62,000 | A$34,000-46,000 |
| All-electric off-grid (28+ kWh/day) | 8-12 | 50-80 (Li) | A$65,000-95,000 | A$50,000-72,000 |
Add A$3,500-7,000 for a Honda EU22i, Pramac, or Yamaha EF6300iSE diesel/petrol generator (mandatory Tasmania, recommended elsewhere).
Where most Australian off-grid systems get under-sized
Three common mistakes from CEC accreditor and Going Off Grid post-mortems:
- No allowance for summer panel temperature. Module STC ratings assume 25°C cell temp; mainland summer cell temps run 55-70°C. PV output drops 12-16% from STC at noon in January. Bake that into the PSH calculation or use PVGIS PVOUT (which already accounts for thermal losses).
- One-day autonomy on a mainland east-coast property. Two-day autonomy is the AS/NZS 4509.2 minimum; one-day will leave you generator-dependent every cloudy week.
- Bore pump direct-drive expectations. A 1.5 kW bore pump might draw 4-5 kW for 3-5 seconds at start. The inverter has to swallow that surge or the pump won’t turn over. Selectronic SP PRO and Victron Quattro both spec 200%+ surge for 5 seconds — generic Chinese hybrids often don’t.
Pair this with the battery bank calculator, charge-time calculator, and wire-size calculator
This Australian off-grid calculator gives the three headline numbers (PV kW, bank kWh, inverter kW). The battery bank calculator drills into Ah at 24 V or 48 V. The charge-time calculator validates recovery after a 2-day overcast stretch. The wire-size calculator picks AS/NZS 3000-compliant CSA in mm² — Australian DC runs are often long (hundreds of metres on rural properties) and undersized cabling is the #1 cause of off-grid voltage-drop complaints.
Sources
- Bureau of Meteorology — Daily Global Solar Exposure — Australian peak-sun-hour data by station
- Clean Energy Council — Stand-alone Power System Design Guidelines — CEC accreditation reference for off-grid design
- AS/NZS 4509.2 — Stand-alone power systems Part 2: System design — Australian / NZ off-grid design standard
- AS/NZS 4777 — Grid-connect inverters — applied to AC-coupled hybrid off-grid configurations
- Clean Energy Regulator — STC and Cheaper Home Batteries Program — federal incentive register
- AER State of the energy market — residential consumption benchmarks
- Selectronic SP PRO product documentation — Australia’s leading off-grid inverter charger