Use this rooftop solar system sizing calculator to turn operational assumptions into a clear planning estimate. Enter values that match your own workload or site, then review the main result, supporting metrics, and interpretation. The calculation runs locally in your browser and exposes every major variable, making it useful for scenario comparison, budgeting, and early-stage design. Results remain estimates and should be checked against measured performance and project-specific constraints.
The calculated DC capacity is the array size needed under the entered solar resource and net efficiency. Panel count rounds up because partial panels are not used.
Planning estimate only. Confirm important decisions with measured data, provider documentation, equipment specifications, and qualified professionals where appropriate.
To offset 80% of 12,000 kWh/year with 4.5 peak sun hours and 80% net efficiency requires 7.31 kW DC. With 400 W panels, round up to 19 panels, or 7.60 kW.
Yes, if you intentionally plan annual generation above current annual use, subject to local rules and site constraints.
No. Compare the panel count and dimensions with usable, code-compliant roof area.
Panel count is rounded up to a whole panel.
Prefer a full year of bills because seasonal electricity use can vary substantially.
No. Battery energy and inverter power require separate sizing checks.
| Item | Meaning |
|---|---|
| Input | Effect on size |
| Annual use | Higher use increases required size |
| Offset target | Higher offset increases required size |
| Peak sun hours | More solar resource reduces required size |
| Net efficiency | More retained energy reduces required size |