How Many Solar Panels Do I Need?

The short answer: most Australian homes need between 15 and 25 solar panels. But the right number for your home depends on three things: how much electricity you use, how much roof space you have, and what panels you choose.

Here's how to work it out.

The Quick Method: Size by Your Electricity Bill

Your quarterly electricity bill is the fastest way to estimate your system size. Find your daily usage in kWh (it's usually printed on your bill), then match it to a system size:

These are estimates for Sydney. If you're in a sunnier part of NSW, you might need slightly fewer panels. Cloudier areas might need a few more.

The Detailed Method: Step by Step

Step 1: Find your daily electricity usage

Check your electricity bill for “average daily usage” in kWh. If it only shows total kWh for the billing period, divide by the number of days. For example: 1,800 kWh over 90 days = 20 kWh per day.

Step 2: Decide how much you want solar to cover

Most homeowners aim to offset 70-100% of their electricity with solar. You don't need to cover 100% because you won't use all the solar power you generate (some gets exported to the grid). Covering 80% of your usage is usually the sweet spot for value.

Step 3: Calculate system size

In Sydney, each 1kW of solar produces roughly 4 kWh per day on average (accounting for seasons, clouds, and panel orientation). So:

System size (kW) = Daily usage (kWh) ÷ 4

Example: If you use 25 kWh per day, you need roughly a 6.5kW system. The closest standard size is 6.6kW.

Step 4: Convert to number of panels

Modern solar panels are typically rated at 370W to 440W each. Using 400W panels (a common choice in 2026):

Number of panels = System size (W) ÷ Panel wattage (W)

Example: 6,600W ÷ 400W = 16.5 panels. Round up to 17 panels.

How Much Roof Space Do You Need?

Each solar panel is roughly 1.7m x 1.0m (1.7 square metres). Here's how much usable roof space you need:

Keep in mind that “usable” roof space excludes areas shaded by trees, antennas, chimneys, or neighbouring buildings. Panels also need setbacks from the roof edges. Your installer will assess this during the site inspection.

Does Roof Direction Matter?

Yes, quite a lot.

• North-facing: Ideal. Maximum sun exposure throughout the day. Produces the most energy overall.
• East-facing: Strong morning production. Good if you use lots of power in the morning (breakfast, getting ready for work).
• West-facing: Strong afternoon production. Great if you're home in the afternoons or have a pool pump running.
• East + West split: Spreads production across the day. Often the best option for families who use power morning and afternoon.
• South-facing: Least productive. Loses roughly 30% compared to north. Avoid if possible, but can still be worthwhile if it's your only option.

If you don't have a north-facing roof, don't stress. An east/west split system still produces excellent results and often matches real-world usage patterns better than pure north.

What About Shading?

Shading is the silent killer of solar performance. Even partial shade on one panel can reduce the output of an entire string of panels (they're connected in series).

Solutions for shading:

• Microinverters (like Enphase) let each panel work independently, so shade on one panel doesn't drag down the others
• Optimisers (like SolarEdge) achieve a similar effect at lower cost
• Panel placement to avoid shaded areas entirely
• Tree trimming if possible and permitted

A good installer will use satellite imagery and shading analysis tools to identify any issues before quoting.

Single Phase vs Three Phase

Most residential homes in Sydney are single phase, which limits your inverter size to 5kW. You can still install more than 5kW of panels (a 6.6kW panel array on a 5kW inverter is the most popular combination) because panels rarely produce at full capacity.

If you have three-phase power (common in newer homes and some older properties with upgrades), you can install larger systems up to 15kW or more. Three-phase is also required for larger systems and some battery setups.

Check your switchboard or ask your electrician if you're not sure which you have.

Sizing by Household

As a rough guide based on typical Sydney households:

• 1-2 people, apartment or small home: 3-5kW (10-14 panels)
• 2-3 people, average home: 5-6.6kW (14-17 panels)
• 3-4 people, family home: 6.6-8kW (17-20 panels)
• 4+ people, large home or pool: 8-13kW (20-30 panels)

If you're planning to add an electric vehicle, heat pump hot water, or other electric appliances in the future, size your system a bit larger now. The marginal cost of adding a few extra panels during installation is much less than retrofitting later.

Common Mistakes to Avoid

Undersizing your system

Going too small to save money often backfires. You still pay for the installation, scaffolding, and electrical work. Adding a few extra panels costs relatively little and significantly increases your savings. The sweet spot is covering 80-100% of your current usage, plus a margin for future growth.

Ignoring future needs

Electric vehicles, heat pump hot water systems, induction cooktops, and home batteries are all becoming mainstream. If any of these are on your radar in the next 5-10 years, factor them into your sizing now.

Only looking at panel count

20 cheap 330W panels produce less than 15 premium 440W panels. Focus on total system output (kW), not the number of panels. Higher-wattage panels also use less roof space, which matters on smaller roofs.

The Bottom Line

For most Sydney homes, a 6.6kW system (15-18 panels) is the best balance of cost, output, and roof space. If your bills are high or you're planning electric upgrades, go bigger.

The best way to get the exact right number? Have a qualified installer assess your roof, review your electricity bills, and design a system matched to your usage.