A 1-watt solar panel generates approximately 1 watt of electricity per hour under ideal conditions, equating to about 24 watt-hours in a single day. Factors like weather, geographic location, and time of year influence this efficiency. This amount translates to about 730 to 1460 watt-hours annually. Quick answer: A modern 400W solar panel produces about 1. residential median of 5 peak sun hours. A 10 kW system produces about 42 kWh/day. 70. Estimate daily, monthly, and yearly solar energy output (kWh) based on panel wattage, quantity, sunlight hours, and efficiency factors. Typical total efficiency ranges 75–90%. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations. PVWatts ® is a registered trademark by.