Solar Panel Sizing Calculator Formula
Understand the math behind the solar panel sizing calculator. Each variable explained with a worked example.
Formulas Used
Required Panel Wattage
panel_watts = daily_energy_wh / (sun_hours * eff_fraction)Panel Current (12V system)
panel_current_12v = daily_energy_wh / (sun_hours * eff_fraction) / 12Daily Generation
daily_generation_wh = daily_energy_wh / eff_fractionVariables
| Variable | Description | Default |
|---|---|---|
daily_energy_wh | Daily Energy Needed(Wh) | 50 |
sun_hours | Peak Sun Hours(hours) | 5 |
system_efficiency_pct | System Efficiency(%) | 75 |
eff_fraction | Derived value= system_efficiency_pct / 100 | calculated |
How It Works
Solar Panel Sizing
Formula
Panel Watts = Daily Energy / (Sun Hours x Efficiency)
Efficiency accounts for charge controller losses, wiring, temperature derating, and panel degradation. Typical system efficiency is 70-80%.
Worked Example
50 Wh daily energy need, 5 peak sun hours, 75% system efficiency.
- 01Required generation = 50 / 0.75 = 66.7 Wh
- 02Panel watts = 66.7 / 5 = 13.3 W
- 03At 12 V: current = 13.3 / 12 = 1.11 A
Frequently Asked Questions
What are peak sun hours?
Equivalent hours of full 1000 W/m2 sunlight per day. Varies by location and season, typically 3-7 hours.
Why 75% efficiency?
Losses from charge controller (5-15%), wiring (2-5%), temperature (5-15%), and dust/shading (5-10%) add up.
MPPT vs PWM charge controller?
MPPT controllers are 95-98% efficient. PWM is simpler but 75-85% efficient. MPPT gains are largest when panel voltage exceeds battery voltage.
Ready to run the numbers?
Open Solar Panel Sizing Calculator