Everything you need to calculate solar panels, battery capacity, inverter size and system cost for an off-grid or hybrid solar installation in Australia.
By Rainbow Power Company — Australia's off-grid solar specialists since 1987.
An off-grid solar system (also called a standalone power system or RAPS — Remote Area Power Supply) generates and stores all electricity on-site, with no connection to the electricity grid. It consists of solar panels, a battery bank, an inverter/charger and usually a backup generator for extended cloudy periods.
Off-grid systems are the right choice when:
A hybrid solar system includes solar panels and battery storage but stays connected to the grid as a backup. This is a better choice for most suburban homes that want to reduce bills without complete independence.
Not sure which is right for you? Try the free calculator →
This is the most important step. Everything else — panel count, battery size, inverter capacity — flows from your daily kilowatt-hour (kWh) figure.
Add up this formula for every appliance in your home. Common energy consumers and their typical loads:
| Appliance | Typical Watts | Hours/Day | kWh/Day |
|---|---|---|---|
| Refrigerator (medium, frost-free) | 150 W | 8 h | 1.2 kWh |
| Split-system air conditioner (2.5 kW) | 850 W | 6 h | 5.1 kWh |
| LED lights (10 bulbs, whole house) | 100 W | 5 h | 0.5 kWh |
| Heat pump hot water system | 500 W | 3 h | 1.5 kWh |
| Washing machine | 500 W | 1 h | 0.5 kWh |
| Chest freezer | 80 W | 8 h | 0.6 kWh |
| 55" LED television | 80 W | 4 h | 0.3 kWh |
| Laptop computer | 45 W | 6 h | 0.3 kWh |
| Pressure water pump | 750 W | 1 h | 0.75 kWh |
| Pool pump (0.75 kW) | 750 W | 6 h | 4.5 kWh |
| EV charger (Level 2, 7.4 kW) | 7,400 W | 2 h | 14.8 kWh |
| Microwave oven | 1,200 W | 0.3 h | 0.4 kWh |
| Induction cooktop (2 burners) | 3,000 W | 1 h | 3.0 kWh |
| Router / modem (24/7) | 15 W | 24 h | 0.4 kWh |
| Household Type | Daily kWh | Notes |
|---|---|---|
| Small cabin / holiday house (no A/C) | 2–5 kWh | Basic lighting, fridge, water pump |
| 2-bedroom home (no A/C or pool) | 5–10 kWh | Typical rural property |
| 3–4 bedroom home with A/C | 10–20 kWh | Most common off-grid sizing target |
| Large home with pool + EV | 25–40 kWh | Significant system required |
| Farm / agricultural property | 20–80 kWh | Highly variable — pumps, workshops, irrigation |
Tip: Don't forget seasonal variation. Air conditioning in Queensland summer can triple your daily consumption vs winter. Size for your worst-case season.
Once you have your daily kWh figure, use this formula to calculate required solar panel capacity:
Example: A home using 12 kWh/day in Brisbane (5.2 peak sun hours):
In practice, off-grid systems are over-sized by 20–50% to handle cloudy days and seasonal variation. A 12 kWh/day home would typically receive a 4–5 kW solar array recommendation.
Peak sun hours (PSH) represent the daily equivalent hours of full sun (1,000 W/m²). This varies significantly by location and season.
| City / Region | Annual Average PSH | Winter PSH | Summer PSH |
|---|---|---|---|
| Darwin, NT | 5.8 | 7.5 | 4.5 |
| Perth, WA | 5.5 | 4.0 | 7.0 |
| Brisbane, QLD | 5.2 | 4.5 | 6.0 |
| Adelaide, SA | 5.0 | 3.5 | 6.5 |
| Sydney, NSW | 4.9 | 3.8 | 6.2 |
| Canberra, ACT | 4.7 | 3.0 | 6.5 |
| Melbourne, VIC | 4.4 | 2.8 | 6.2 |
| Hobart, TAS | 3.9 | 2.5 | 5.5 |
| Remote Outback (NT/WA/SA) | 6.0–6.5 | 5.5 | 7.0 |
| Northern NSW (Nimbin, Byron) | 5.0 | 4.2 | 6.0 |
Source: Australian Bureau of Meteorology (BOM) solar irradiance data. Always size using winter figures for critical off-grid reliability.
Your battery bank must store enough energy to power your home through the night and through cloudy days (days of autonomy).
| Battery Type | Usable DoD | Typical Lifespan | Best For |
|---|---|---|---|
| Lithium iron phosphate (LiFePO4) | 80–90% | 10–15 years | Most off-grid applications — preferred choice |
| AGM lead-acid | 50% | 4–7 years | Budget installs, low-use cabins |
| Gel lead-acid | 50% | 5–8 years | Moderate-use off-grid |
| OPzS flooded lead-acid | 60% | 12–20 years | Large commercial/farm systems |
Example — 12 kWh/day home, 2 days autonomy, lithium battery:
This would typically be met by a 30 kWh lithium battery system (e.g., two 15 kWh units). Most quality off-grid lithium systems in Australia come from BYD, Pylontech, BMZ, or custom lithium banks assembled by specialists like Rainbow Power Company.
The inverter converts DC battery power to 240V AC power for your home. For off-grid systems, you need a hybrid inverter/charger that also accepts solar input (MPPT) and can charge batteries from a generator.
Costs vary significantly based on system size, battery chemistry, brand and remoteness of installation. As a rough guide for 2025:
| System Size | Suitable For | Approximate Cost (AUD) |
|---|---|---|
| 3 kW solar + 10 kWh lithium | Small cabin, 2–5 kWh/day | $15,000 – $25,000 |
| 5 kW solar + 20 kWh lithium | Small home, 5–10 kWh/day | $25,000 – $40,000 |
| 8 kW solar + 30 kWh lithium | Family home, 10–15 kWh/day | $40,000 – $60,000 |
| 12 kW solar + 50 kWh lithium | Large home + pool, 20+ kWh/day | $60,000 – $90,000 |
| 20+ kW solar + 100+ kWh | Farm / agricultural | $100,000+ |
These figures include supply and installation. Government rebates (STCs under the Small-scale Renewable Energy Scheme) reduce costs by $2,000–$8,000 depending on system size and location. Grid connection avoided costs (which can exceed $50,000 for remote properties) make off-grid economics compelling.
| Factor | Off-Grid | Hybrid (Grid-Connected) |
|---|---|---|
| Grid connection available? | No (or too expensive) | Yes |
| Ongoing electricity bills | None | Significantly reduced |
| System cost | Higher (larger battery) | Lower (smaller battery, grid backup) |
| Reliability | Depends on system sizing + generator | Very high (grid as backup) |
| Generator required? | Recommended | No |
| Best for | Remote properties, farms | Suburban / semi-rural homes |
Rather than doing all this manually, use our free AI-powered off-grid solar load calculator. In 3–5 minutes, Bowie our AI assistant will:
Rainbow Power Company's engineers — with over 35 years of off-grid solar experience — review every submission and follow up with a detailed system recommendation tailored to your specific property.
Takes 3–5 minutes. No obligation. Get a personalised energy report emailed to you.
Start the Calculator →Rainbow Power Company Pty Ltd — ABN 74 003 323 420 — 1 Alternative Way, Nimbin NSW 2480 — rpc.com.au