SOLAR
How to Estimate Solar Energy Production
Contractor method for estimating a solar array's kWh production by panel count and sun.
Solar production estimates fail on the sun hours and the loss factor. The panel math is easy; the real sun and the system losses determine how many kWh you actually produce.
THE SHORT ANSWER
How do you estimate solar production?
Multiply panels × watts ÷ 1000, then × sun hours × (1 − loss). 20 panels of 400 W at 4.5 sun hours with 20% loss produce ~28.8 kWh/day.
Count the panels and wattage
Count the panels and their peak wattage. A 400 W panel is the common modern rating. Multiply panels × watts ÷ 1000 for the kW capacity.
- Count the panels
- Confirm the panel wattage
- Note the array orientation
- Check tilt and shading
Enter the sun hours
Use the equivalent peak sun hours for the site — roughly 4-5 in most of the US, less in cloudy regions. This is the daily production window.
Apply the loss factor
Temperature, wiring and the inverter reduce output by 10-25%. Use the Solar Energy Production Calculator to compute daily, monthly and annual kWh.
Note the limits
These are preliminary estimates, not a production guarantee. A professional solar design accounts for orientation, tilt and site-specific shading.