Solar Panel Output Calculator
Calculate daily, monthly, and yearly energy production from your solar panels. Enter panel specs and sun hours for accurate output estimates.
Formula & How It Works
Daily Output (kWh) = (Panels × Wattage × Peak Sun Hours × Efficiency) / 1000
Multiply the number of panels by their wattage to get total system size in watts. Multiply by peak sun hours and system efficiency to get daily energy production in watt-hours. Divide by 1000 for kWh. Monthly output is daily × 30; yearly is daily × 365. System efficiency accounts for inverter, wiring, temperature, and soiling losses.
Solar Panel Output Reference Table
400W panels at 5 peak sun hours, 80% efficiency:
| System Size | Panels (400W) | Daily kWh | Monthly kWh | Yearly kWh |
|---|---|---|---|---|
| 2 kW | 5 panels | 8 kWh | 240 kWh | 2,920 kWh |
| 4 kW | 10 panels | 16 kWh | 480 kWh | 5,840 kWh |
| 6 kW | 15 panels | 24 kWh | 720 kWh | 8,760 kWh |
| 8 kW | 20 panels | 32 kWh | 960 kWh | 11,680 kWh |
| 10 kW | 25 panels | 40 kWh | 1,200 kWh | 14,600 kWh |
| 15 kW | 38 panels | 60 kWh | 1,800 kWh | 21,900 kWh |
| 20 kW | 50 panels | 80 kWh | 2,400 kWh | 29,200 kWh |
Factors Affecting Solar Panel Output
- Temperature: Panels lose 0.3-0.5% efficiency per °C above 25°C (STC rating)
- Shading: Even 10% shading on one panel can reduce string output by 30-50%
- Tilt angle: Optimal tilt equals your latitude; flat panels lose 15-25% output
- Orientation: South-facing is optimal; east/west-facing lose 15-20%
- Soiling: Dust, pollen, and snow can reduce output 5-15% if not cleaned
- Inverter efficiency: String inverters are 96-98%; microinverters handle shading better
- Panel degradation: Panels lose ~0.5% output per year; 25-year warranty guarantees 80%+
Frequently Asked Questions
How much power does a 400W solar panel produce per day?
A single 400W solar panel produces approximately 1.6 kWh per day at 5 peak sun hours and 80% system efficiency. Over a month, that is about 48 kWh, and over a year, about 584 kWh. In sunnier locations with 6+ sun hours, daily output can reach 1.9+ kWh.
How much does a 10 kW solar system produce?
A 10 kW system (25 × 400W panels) at 5 peak sun hours and 80% efficiency produces about 40 kWh per day, 1,200 kWh per month, and 14,600 kWh per year. At $0.15/kWh, that is approximately $2,190 in annual savings.
How many kWh does a solar panel produce per month?
A single 400W panel produces about 48 kWh per month at 5 sun hours and 80% efficiency. A typical 8 kW residential system (20 panels) produces about 960 kWh per month. Actual output varies seasonally - summer months may produce 40-60% more than winter months.
What are peak sun hours and how do I find mine?
Peak sun hours are the equivalent hours per day when solar irradiance reaches 1,000 W/m². The US ranges from 3-7 peak sun hours. The Southwest (Arizona, Nevada, California) gets 6-7 hours, the South gets 5-6, the Midwest gets 4-5, and the Pacific Northwest gets 3-4. Check NREL's PVWatts calculator for your specific location.
Why is my solar panel output lower than expected?
Common causes include panel shading, high temperatures, dirty panels, suboptimal tilt/orientation, inverter clipping, and panel degradation. Also, STC ratings (nameplate wattage) are measured at 25°C; real-world conditions are typically 10-20% lower. Use 80% efficiency as a realistic default.