How Much Solar Do I Actually Need? (Australian Sizing Guide)

One of the most common mistakes Australian homeowners make when going solar is either undersizing (leaving significant savings on the table) or oversizing (paying for capacity that generates more export than they can use profitably). The right size depends on five key factors.

Step 1: Find Your Daily Consumption

Your electricity bill shows your consumption in kWh, usually as a quarterly or annual figure. To find your daily average:

• Take your quarterly kWh total and divide by 91 (days)
• Or take your annual kWh total and divide by 365

Typical Australian household consumption by home type:

• 1–2 bedroom apartment/unit: 8–15 kWh/day
• 3 bedroom house (no pool, gas appliances): 15–22 kWh/day
• 3–4 bedroom house (air conditioning, electric hot water): 22–35 kWh/day
• 4–5 bedroom house (pool, electric everything): 35–55 kWh/day

Step 2: Calculate How Much Solar You Need to Generate

Solar panels generate electricity during daylight hours. The key metric is peak sun hours — the number of hours per day your location receives sunlight equivalent to 1,000 W/m² (full-intensity sun).

Australian peak sun hours by city:

• Adelaide: 4.8–5.3 peak hours/day (annual average)
• Sydney: 4.4–4.8 peak hours/day
• Melbourne: 4.0–4.5 peak hours/day
• Brisbane: 5.0–5.5 peak hours/day
• Perth: 5.3–5.8 peak hours/day

To calculate the system size you need:

System size (kW) = Daily consumption (kWh) ÷ Peak sun hours × Self-consumption factor

The self-consumption factor accounts for the fact that you won't use all solar power generated in real time. For a home occupied during the day: 0.8–1.0. For a home empty during the day: 1.2–1.5 (you'll need to oversize to maximise self-consumption via battery or export).

Step 3: Understand the Inverter Limit

Your solar panels connect to an inverter, and most residential single-phase inverters are limited to 10 kW export by Australian standards (AS/NZS 4777). Your network distributor may impose lower limits — SA Power Networks limits single-phase to 5 kW export and three-phase to 15 kW export without prior approval.

This is why 10–13 kW panel arrays with a 10 kW inverter are common — you can install more panels than the inverter's rated output to optimise generation during non-peak hours.

Common System Sizes and Who They Suit

• 6.6 kW (20 panels): The most popular system in Australia. Suits a 3-bedroom home using 18–28 kWh/day. Generates roughly 25–30 kWh/day in Adelaide.
• 10 kW (30 panels): Suits larger homes or homes with a pool, EV, or electric hot water. At the single-phase inverter limit for most networks.
• 13.2 kW (40 panels): For homes with very high consumption or planning significant future load growth. Requires three-phase power or network approval.

If You're Planning to Add a Battery

Size your solar system to match your battery charging needs as well as your daytime load. A 10 kWh battery needs roughly 3–5 kWh of excess solar per day (beyond what you use during the day) to fully charge from solar alone. If you're in Melbourne, you may need a larger array to reliably charge a battery through winter.