Solar Panel Installation: How Many Panels Do I Need?

How to Size a Solar System

Start with your annual electricity usage in kilowatt-hours (kWh). Check your utility bills — the average Australian home uses 6,000-8,000 kWh per year, while the average US home uses about 10,500 kWh.

Divide your annual usage by the peak sun hours for your location (multiplied by 365). For example, Brisbane receives about 5.2 peak sun hours per day. A home using 7,000 kWh per year needs: 7,000 ÷ (5.2 × 365) = 3.7 kW system.

Divide the system size by the wattage of individual panels. Modern residential panels produce 370-425 watts each. A 3.7 kW system needs: 3,700 ÷ 400 = about 10 panels.

Roof Space Requirements

A standard residential solar panel measures roughly 1.7m × 1.0m (5.5 × 3.3 feet), covering about 1.7 square metres (18 sq ft) per panel.

A 10-panel system needs approximately 17 square metres (180 sq ft) of unshaded roof space. North-facing roofs (in Australia) or south-facing roofs (in the US) produce the most energy.

Shading from trees, chimneys, or neighbouring buildings can significantly reduce output. Even partial shading on one panel can reduce the output of an entire string. Modern micro-inverters or power optimisers help mitigate this.

Solar Panel Costs in 2026

In Australia, a 6.6 kW system (most popular residential size) costs $5,000-$9,000 after the federal STC rebate. Premium panels and micro-inverters sit at the higher end.

In the United States, a 6 kW system costs $12,000-$18,000 before the 30% federal tax credit, bringing the net cost to $8,400-$12,600.

Battery storage adds $5,000-$15,000 depending on capacity. A 10 kWh battery (like the Tesla Powerwall) typically costs $10,000-$13,000 installed and covers overnight usage for most households.

Payback Period and Savings

The typical payback period for solar in Australia is 3-5 years thanks to high electricity prices ($0.25-$0.35/kWh) and generous feed-in tariffs in some states.

In the United States, payback periods range from 6-10 years depending on state incentives, utility rates, and net metering policies. States like California, Massachusetts, and New York offer the best returns.

After payback, solar panels continue generating free electricity for another 15-20 years. Most panels come with 25-year performance warranties, guaranteeing at least 80% of original output.

Solar also increases home value. Studies show homes with solar sell for 3-4% more on average, adding $15,000-$30,000 to the value of a typical home.