How Many Solar Panels Do I Need?

The short answer: most Australian homes land on a 6.6 kW system — about 15 panels. The right size for you comes from your electricity bill, not a rule of thumb. Here's the three-step method, with a worked example.

Step 1: Turn your bill into annual kWh

Grab a recent quarterly bill. Subtract the supply charge (roughly 88c a day in NSW, or ~$80 a quarter), then divide what's left by your usage rate (about 34c/kWh in NSW on the 2026–27 benchmark). Multiply the quarter's kWh by four.

Step 2: Convert annual kWh to system kW

Each kW of panels generates roughly 3.9 kWh a day on average across Australia — so about 1,424 kWh a year per kW (3.9 × 365). Divide your annual kWh by 1,424 to get the system size that roughly covers your usage.

Step 3: Convert kW to panel count

Modern residential panels are typically 400–450W (440W is a common 2026 standard). Divide the system size in watts by the panel wattage:

Worked example: $600 quarterly bill in NSW

1. Quarterly usage: $600 − ~$80 supply charge = $520 ÷ 34c/kWh ≈ 1,529 kWh/quarter.
2. Annual usage: 1,529 × 4 ≈ 6,118 kWh/year (~16.8 kWh/day).
3. System size: 6,118 ÷ 1,424 ≈ 4.3 kW.
4. Panels: 4,300W ÷ 440W ≈ 10 panels.

So 10 panels would roughly cover this household's annual usage. In practice, most installers would quote a 6.6 kW system (15 panels) — the extra capacity is cheap (around $1,000/kW installed after STCs), covers future usage growth like an EV, and suits a standard single-phase inverter.

Don't oversize for the feed-in tariff

It's tempting to max out the roof, but with typical flat feed-in tariffs at just 3–4c/kWh (Finder reports 45% of solar owners get 5c or less), exported power earns very little. Size to cover your usage — and add a battery if you want to use the surplus yourself. Oversizing only pays when you can self-consume the extra.

Roof direction effects

• North-facing panels generate the most total energy over a year in Australia — this is the ideal orientation.
• East–west split arrays generate less in total, but produce more in the morning and late afternoon when households actually use power — often a better match for self-consumption.
• South-facing panels are the poorest performers and best avoided unless there's no alternative.
• Shade matters more than direction: a shaded north-facing array will underperform a clear east-facing one. Chimneys, antennas and neighbouring trees all count.
• Tilt near your latitude is ideal, but standard roof pitches are close enough — installers rarely need special tilt frames.

Quick rules of thumb

• 1–2 person household, low usage (~10 kWh/day): 4–5 kW, ~10–12 panels.
• Family home, average usage (~16–20 kWh/day): 6.6 kW, 15 panels — the Australian sweet spot.
• High usage with pool, ducted air-con or EV (~30+ kWh/day): 10–13 kW, 23–30 panels (may need three-phase power).

Last updated: September 2026.