Solar System Size Calculator
Estimate the solar panel system size in kilowatts needed to cover your household's daily electricity usage.
Your results
Calculation breakdown
- System size
- kW = daily usage (kWh) / (sun hours × system efficiency)
- Panel count
- Panels = system size (W) / panel wattage, rounded up
Worked example
A household using 18 kWh a day, with 4.5 peak sun hours and 80% system efficiency, needs about a 5 kW system, roughly 12 panels of 440 W.
Assumptions
- Sun hours vary by location and season; use a conservative local annual average.
- Does not account for shading, roof orientation or panel degradation over time.
- Actual generation will vary day to day with weather.
How this calculator works
Enter your average daily electricity usage in kWh and your local average sun hours to estimate the solar system size (in kW) required to offset your usage. It also estimates the number of panels based on a panel wattage you specify.
Frequently asked questions
Where do I find my daily usage?
Your electricity bill shows total kWh used over the billing period; divide by the number of days to get a daily average.
What are 'peak sun hours'?
This is the average number of hours per day of full-strength sunlight for your location, typically 4–5.5 hours across most of Australia.
Does this account for system losses?
Yes, you can adjust the system efficiency input to allow for inverter losses, shading and panel degradation.
Actual prices, usage, efficiency and savings vary by provider, equipment, location and behaviour.