Solar Panel Energy Calculator
Daily energy yield and battery charging
Required Parameters
Waiting for input data...
Quick Answer
Daily energy (Wh) = Panel wattage × Peak sun hours × System efficiency (typically 0.75-0.85).
Design Notes
Peak sun hours vary by location (2-7 hours). System losses include: panel degradation (~2%/yr), wiring (2-3%), charge controller (5-15%), temperature derating (10-25% in hot climates). For battery sizing, plan for 2-3 days autonomy. MPPT controllers extract 15-30% more energy than PWM types.
Common Mistakes
- 1
Using panel rated wattage directly — real output is 75-85% of STC rating.
- 2
Ignoring temperature derating — panels lose ~0.4%/°C above 25°C.
- 3
Undersizing battery storage — cloudy days can reduce output by 70-80%.
Knowledge Base
How do I calculate solar panel daily energy output?
Daily energy (Wh) = Panel wattage (STC) × Peak Sun Hours × System efficiency (0.75-0.85). A 100W panel in a location with 5 peak sun hours: 100 × 5 × 0.80 = 400 Wh/day. Peak sun hours represent hours of equivalent 1000 W/m² irradiance — not total daylight hours.
What are peak sun hours?
Peak Sun Hours (PSH) = total daily solar irradiation divided by 1000 W/m². A location receiving 5000 Wh/m²/day has 5 PSH. Values by region: Northern Europe 2-3, Central US 4-5, Southern US/Australia 5-6, Sahara/Middle East 6-7. Check pvwatts.nrel.gov for your exact location.
What losses reduce solar panel output?
Temperature derating: -0.3 to -0.5%/°C above 25°C (can lose 10-25% in summer). Wiring losses: 2-3%. Charge controller: PWM loses 15-25%, MPPT loses 5-10%. Panel soiling/dust: 2-5%. Inverter efficiency: 92-97%. Panel degradation: ~0.5-0.8%/year. Total system loss: typically 15-25%.
MPPT vs PWM charge controller?
MPPT (Maximum Power Point Tracking) converts excess voltage to current, extracting 15-30% more energy than PWM. Essential when panel voltage significantly exceeds battery voltage (e.g., 36V panel → 12V battery). PWM is cheaper but wastes the voltage difference. MPPT pays for itself in larger systems (>200W).
How do I size a battery bank for solar?
Battery capacity (Ah) = Daily energy (Wh) × Days of autonomy / (Battery voltage × Depth of Discharge). For 400Wh/day with 2 days autonomy, 12V battery, 50% DoD: 400 × 2 / (12 × 0.5) = 133 Ah. Use LiFePO4 batteries for 80% DoD and 2000+ cycles vs lead-acid at 50% DoD and 500 cycles.
What size solar panel do I need?
Panel size (W) = Daily energy needed (Wh) / (Peak sun hours × System efficiency). For 1000 Wh/day in 5 PSH at 80% efficiency: 1000 / (5 × 0.80) = 250W. Always oversize by 20-30% to account for cloudy days, seasonal variation, and panel degradation over time.
Related Engineering Tools
Battery Life Calculator
Estimate runtime from capacity and load current
Three Phase Calculator
Real, apparent, and reactive power
Transformer Turns Ratio Calculator
Voltage, current, and impedance transformation
LDO Voltage Regulator Calculator
Dropout, power dissipation, and thermal analysis