Solar Panel Output Calculator
Estimate daily, monthly and annual generation from a solar array.
Please note: Estimates for planning only. Actual solar output depends on your latitude, roof orientation, shading, weather and equipment. Get a site-specific assessment and quotes before committing.
What the Solar Panel Output Calculator does
Solar output is system capacity multiplied by peak sun hours and a derate factor covering inverter, wiring, heat and soiling losses. Panels also degrade slowly, so the lifetime total is a compounding series rather than year one multiplied by the term.
Formula
Daily kWh = System kW × Peak sun hours × (1 − Losses) × (1 − Shading)Annual kWh = Daily kWh × 365Year n output = Year 1 × (1 − Degradation)^(n−1)Capacity factor = Annual kWh ÷ (System kW × 8,760)
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| System size | kW | Yes | Accepts more than 0. |
| Peak sun hours per day | one of 7 options | Yes | Average daily equivalent hours of full-strength sunlight for your location. |
| System losses | % | Yes | Inverter, wiring, soiling, heat and mismatch losses combined. 20% is typical. |
| Annual panel degradation | % | Yes | Panels lose roughly 0.5% output a year. |
| Years to project | number | Yes | Accepts 1 or more, up to 40. |
| Additional shading loss | % | Optional | — |
How to use it
- Choose Peak sun hours per day.
- Enter System size, System losses, Annual panel degradation and Years to project.
- Optionally add Additional shading loss.
- Select Calculate.
Worked example
A 6 kW system, 4.5 peak sun hours, 20% losses, 0.5% degradation over 25 years.
- Size
- 6 kW
- Sun hours
- 4.5
- Losses
- 20
- Degradation
- 0.5
- Years
- 25
Year 1 produces 7,884 kWh. Over 25 years the system delivers 185,715 kWh, ending at 88.7% of its original output.
Frequently asked questions
What is a capacity factor?
The share of theoretical maximum output actually achieved. Residential solar typically runs 15–20%; wind is 25–45%; nuclear exceeds 90%.
How quickly do panels degrade?
Around 0.5% a year for modern panels, often with a larger first-year drop. After 25 years most still produce 85% or more of their original output.