Solar Panel Output Calculator Formula
Understand the math behind the solar panel output calculator. Each variable explained with a worked example.
Formulas Used
Total Array Size
array_size = total_watts / 1000Estimated Daily Output
daily_kwh = total_watts * sun_hours * eta / 1000Estimated Annual Output
annual_kwh = total_watts * sun_hours * eta / 1000 * 365Variables
| Variable | Description | Default |
|---|---|---|
panel_watts | Panel Rating(W) | 400 |
num_panels | Number of Panels | 10 |
sun_hours | Peak Sun Hours per Day(hours) | 5 |
system_efficiency | System Efficiency (losses)(%) | 80 |
total_watts | Derived value= panel_watts * num_panels | calculated |
eta | Derived value= system_efficiency / 100 | calculated |
How It Works
Solar Panel Energy Estimation
Daily energy output depends on panel capacity, sunlight availability, and system losses.
Formula
Daily kWh = Array size (kW) x Peak sun hours x System efficiency
Peak sun hours represent the equivalent hours of full-intensity (1000 W/m^2) sunlight per day, typically 3-6 hours depending on location and season. System efficiency accounts for inverter losses, wiring, temperature derating, dust, and shading.
Worked Example
10 panels of 400 W each, 5 peak sun hours, 80% system efficiency.
- 01Array size = 400 x 10 = 4000 W = 4.0 kWp
- 02Daily output = 4.0 x 5 x 0.80 = 16.0 kWh/day
- 03Annual output = 16.0 x 365 = 5,840 kWh/year
Frequently Asked Questions
What are peak sun hours in my area?
Peak sun hours vary by location and season. Examples: Phoenix AZ: 6.5, London UK: 2.5, Sydney AU: 5.0, Dubai: 6.0, Berlin: 2.7. Solar resource databases like PVGIS or NREL TMY provide precise local data.
Why is system efficiency only 80%?
The 20% loss includes: inverter efficiency (3-5% loss), cable losses (1-3%), temperature derating (5-15% in hot climates), dust/soiling (2-5%), panel degradation, and mismatch between panels.
How do I size panels for battery charging?
Divide the daily battery energy needed (kWh) by (sun hours x system efficiency) to get the required array size in kW. Add margin for cloudy days and seasonal variation.
Ready to run the numbers?
Open Solar Panel Output Calculator