Complete guide
Solar Panel Calculator: formula, example and decision guide
Estimate array size, panel count and annual production from energy use and solar-resource assumptions. The result updates instantly and keeps every assumption visible.
What the Solar Panel Calculator measures
Estimate array size, panel count and annual production from energy use and solar-resource assumptions.
Use the result to compare scenarios built from the same definitions and time period.
Formula and variables
The calculator applies array kW = daily kWh ÷ peak-sun hours ÷ system efficiency. Each variable is entered in a labeled field and remains visible beside the answer.
array kW = daily kWh ÷ peak-sun hours ÷ system efficiencyWorked example
30 kWh/day, five sun hours and 80% system efficiency needs about 7.5 kW, or 19 whole 400 W panels.
Change one input at a time to see which assumption has the greatest effect on the result.
How to interpret the result
Read the main result together with the detailed rows; the headline number alone does not describe every cost, unit or assumption.
Save comparable scenarios with the copy, link, CSV or PDF controls.
Assumptions and limitations
Use a site-specific solar assessment for shade, orientation, weather, utility rules, roof loads and production guarantees.
Real contracts, measurements, platform rules and professional standards can add inputs that this general-purpose model does not infer.
Accuracy checklist
Confirm units, time periods, fees and source figures before relying on the output.
Round the displayed answer only after the calculation; intermediate values retain full precision.
Calculation audit
| Item | What to review |
|---|---|
| Inputs | Average daily energy use (kWh), Peak sun hours per day, System derate efficiency (%), Panel rating (W), Installed price per watt |
| Equation | array kW = daily kWh ÷ peak-sun hours ÷ system efficiency |
| Example | 30 kWh/day, five sun hours and 80% system efficiency needs about 7.5 kW, or 19 whole 400 W panels. |
| Limit | Use a site-specific solar assessment for shade, orientation, weather, utility rules, roof loads and production guarantees. |
Frequently asked questions
What does this Solar Panel Calculator calculate?
Estimate array size, panel count and annual production from energy use and solar-resource assumptions.
Which formula does it use?
array kW = daily kWh ÷ peak-sun hours ÷ system efficiency
Does it calculate while I type?
Yes. Valid changes update the result automatically without reloading the page.
Which inputs should I verify?
Verify every unit, period, rate and fee against the source you are modeling.
Is the result exact?
Use a site-specific solar assessment for shade, orientation, weather, utility rules, roof loads and production guarantees.
Can I save or share the result?
Yes. Copy, native sharing, WhatsApp, PDF/Print, CSV, comparison and parameterized links are available.
What to keep in mind
Use a site-specific solar assessment for shade, orientation, weather, utility rules, roof loads and production guarantees.
Results display up to 8 decimal places; exported numbers preserve calculation precision. This is a calculation summary, not an official certificate.