Solar Panel Sizing Calculator
Find out exactly how many solar panels you need for your home, RV, or off-grid system. Enter your daily energy usage and panel specs for instant results.
Formula & How It Works
Panels = (Daily kWh × 1000) / (Efficiency / Panel Wattage × Peak Sun Hours)
First, convert your daily energy usage to watt-hours and divide by system efficiency to account for inverter, wiring, and temperature losses. Then divide by the energy one panel produces per day (panel wattage × peak sun hours). Round up to get the number of panels.
Solar Panel Sizing Reference Table
Number of 400W panels needed at 5 peak sun hours, 80% efficiency:
| Daily Usage (kWh) | Monthly Usage (kWh) | Panels Needed | System Size |
|---|---|---|---|
| 10 kWh | 300 kWh | 7 panels | 2.8 kW |
| 20 kWh | 600 kWh | 13 panels | 5.2 kW |
| 30 kWh | 900 kWh | 19 panels | 7.6 kW |
| 40 kWh | 1,200 kWh | 25 panels | 10.0 kW |
| 50 kWh | 1,500 kWh | 32 panels | 12.8 kW |
| 75 kWh | 2,250 kWh | 47 panels | 18.8 kW |
Factors That Affect Solar Panel Count
- Peak sun hours: Varies by location - 3-5 hrs in the North, 5-7 hrs in the South
- Panel wattage: Modern panels range from 350W to 450W; higher wattage = fewer panels
- System efficiency: Typically 75-85% due to inverter losses, wiring, dust, and temperature
- Roof orientation & tilt: South-facing at 30-45° gives optimal production
- Shading: Even partial shade on one panel can reduce entire string output
Frequently Asked Questions
How many solar panels do I need for a 2,000 sq ft home?
A typical 2,000 sq ft home uses about 30-35 kWh per day. At 5 peak sun hours with 400W panels and 80% efficiency, you would need approximately 19-22 panels, totaling a 7.5-8.8 kW system. Adjust based on your actual energy bills.
How many solar panels do I need for an RV?
RVs typically use 3-5 kWh per day. With 100W panels and 5 sun hours at 80% efficiency, you would need 8-13 panels. Many RV owners use 4-6 larger 200W panels on the roof plus portable panels for flexible placement.
What are peak sun hours?
Peak sun hours measure the equivalent number of hours per day when solar irradiance averages 1,000 W/m². Most of the US gets 4-6 peak sun hours daily. The Southwest can reach 6-7 hours, while the Pacific Northwest may see only 3-4.
How does system efficiency affect panel count?
Real-world solar systems lose 15-25% of their rated output due to inverter conversion losses, wiring resistance, dust accumulation, high-temperature derating, and shading. Using 80% efficiency is a safe default for residential systems.
Can I power my whole house with solar panels?
Yes, if you have enough roof space and a battery storage system for nighttime use. A grid-tied system with net metering can offset 100% of your usage. Off-grid systems require batteries sized for 2-3 days of autonomy.