By Ethan BrooksUpdated November 2026
An off grid solar system in Perth gives you power without a utility connection, so you need to size the array, battery bank and inverter to cover your daily loads. This guide walks through the calculations, the parts list and the wiring decisions that matter. By the end, you will have a rough system size you can refine with real numbers from your home.
Step 1: Calculate Your Daily Energy Use
Start with your electricity demand, measured in watt-hours per day. List every appliance you plan to run, its power rating in watts, and how many hours per day it operates. Multiply watts by hours to get watt-hours. Refrigerators cycle, so use the average running figure from the label or a plug-in energy meter instead of the peak rating.
Shopping for one? See our guide: 6 Best DIY Solar Power System Kit Options for Off-Grid Homes (2026).
Add a 20 to 25 percent margin for losses in the battery, inverter and wiring. Perth summers bring heavy air-conditioning loads, so check those separately. If you are unsure of your figures, an electrician or a qualified solar installer can help verify them before you buy anything. A related read: Types of Home Solar Systems: Grid-Tied, Hybrid, Off-Grid.
Step 2: Size the Solar Array for Perth Sun Hours
Divide your daily energy need by the peak sun hours you expect. Perth averages roughly five to six peak sun hours per day across the year, but winter days are shorter and cloudier, so design around the lower winter figure for reliable year-round power. For example, a home needing 6,000 Wh per day with 4 usable winter sun hours needs about 1,500 W of panels before derating. Add extra capacity to cover system losses.
Step 3: Size the Battery Bank and Inverter
Battery capacity should cover at least one or two days of autonomy, depending on how reliable you need the supply to be. Use usable capacity, not nominal, because lithium and lead-acid batteries both have depth-of-discharge limits set by the manufacturer. Check your inverter’s continuous rating against your highest simultaneous load, and make sure it can also handle motor start-up surges from pumps or compressors.
Parts Checklist
- Solar panels sized to your calculated array
- Charge controller rated for the array voltage and current
- Battery bank matched to your autonomy target
- Inverter with adequate continuous and surge capacity
- DC and AC disconnects, fuses or breakers, and correctly sized cable
- Mounting hardware rated for Perth wind loads
For a full parts sequence and wiring layout, see What Is Needed for Off-Grid Solar System: A Step-by-Step Parts Checklist and Wiring Diagram for Off-Grid Solar System: A Step-by-Step Guide.
Step 4: Plan the Wiring and Protection
Most small systems use a 12, 24 or 48 V battery bank. Higher voltage reduces current and cable size for the same power. Wire panels to the charge controller, batteries to the controller and inverter, and keep fuses close to the battery terminals. Compare your layout against Single Line Diagram of Off Grid Solar System: How to Draw One Step by Step before you cut any cable.
Common Mistakes
- Sizing from nameplate ratings instead of measured daily energy use.
- Designing around summer sun hours and running short in winter.
- Ignoring battery depth-of-discharge limits when calculating usable capacity.
- Undersized cable causing voltage drop over long runs.
- Skipping fuses or disconnects, which creates a real fire and shock risk.
Recommended Gear
A quality clamp-on power meter helps you measure real appliance draw before you size anything, which is the most reliable starting point for Step 1. View on Amazon
A multimeter lets you check open-circuit voltage on panels and battery voltage during commissioning. View on Amazon
FAQ
Can I run an off grid solar system in Perth through winter?
Yes, but you need to size the array for the shorter, cloudier winter days rather than summer output. A backup generator or a reduced load plan is common for extended overcast spells.
Do I need a licence to install an off grid system?
Requirements vary by system type and whether it connects to any building wiring. Check current rules with the relevant Western Australian authorities and consult a licensed electrician before connecting anything to your home’s circuits.
How long do the batteries last?
Lifespan depends on chemistry, depth of discharge and temperature. Follow the manufacturer’s cycle ratings and keep the battery within its recommended temperature range, which matters a lot in Perth heat.
Conclusion
An off grid solar system in Perth comes down to measured energy use, winter-based sun hours and matched battery and inverter sizing. Work through each step with real numbers, then have a qualified electrician review the design. Start with the calculations and the rest of the build becomes much clearer.
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About Ethan Brooks
Ethan Brooks is part of our editorial team and reviews and edits our DIY solar power systems guides, checking product details against manufacturer specifications and owner feedback.
