This solar panel calculator estimates how many panels fit your roof, their combined power, and yearly energy production.
Ecology
Solar Panel Calculator
Estimate PV array size from usage, sunlight, losses and panel specs.
Calculator
About this calculator
Formula notes
array power = panel watts × count; annual energy ≈ power × peak-sun-hours × 365 × performance ratio (≈0.75–0.85).
Worked examples
- Example: 14 panels at 450 W give a 6.3 kW array producing roughly 7358 kWh per year at 4.5 peak-sun-hours with a 0.8 ratio.
- For 900 kWh monthly use, 4.5 peak-sun hours, and 80% system efficiency, average required capacity is about 8.33 kW before roof-layout checks.
How to use it
- Enter roof area and panel dimensions.
- Enter panel wattage and local peak-sun-hours.
- Read panel count, array power, and annual energy.
Frequently asked questions
What is the performance ratio?
A 0.75–0.85 factor covering inverter loss, heat, wiring, and dirt.
Where do I find peak-sun-hours?
Solar maps for your region; it is the equivalent hours of full-strength sun per day.
Limits and interpretation
- Monthly averages do not capture seasonal irradiance, shading, orientation, temperature, degradation, or inverter clipping.
- Panel count is not a final electrical or structural design and may be constrained by roof area, code, export limits, and equipment compatibility.