How to Size a Solar System for Your Home (Calculator Guide)
Learn how to size a solar system based on your actual energy usage, roof space, and goals. A practical, calculation-first guide with transparent methodology.
The right solar system size is the one that matches your household’s real energy use — not the biggest one you can fit, and not the one an aggressive salesperson wants to sell you. Start with your electricity bill, not a sales pitch.
Start with your annual usage
Add up 12 months of electricity use from your bills (in kilowatt-hours) and divide by 365. That daily figure is the anchor for everything: your system must generate close to what you use each day to maximise self-consumption.
The basic sizing formula
- Daily usage (kWh) ÷ peak sun hours = required array output (kW)
- Typical output per kW of panels ranges from 3.5–5.5 kWh/day depending on location
- Roof space needed is roughly 5–7 m² per kW
Panel efficiency vs quantity
Premium high-efficiency panels let you fit more capacity on a small roof; standard panels are cheaper per watt but take more space. The best choice depends on your roof and your budget.