A 90-watt solar panel typically generates between 300 to 450 watt-hours of electricity per day, depending on specific conditions such as location, the angle of installation, and weather patterns. Quick answer: A modern 400W solar panel produces about 1. residential median of 5 peak sun hours. 70. Estimate daily, monthly, and yearly solar energy output (kWh) based on panel wattage, quantity, sunlight hours, and efficiency factors. Losses come from inverter efficiency, wiring, temperature, and dirt. solar installer uses is kWh/day = kW × PSH × derate, where the derate factor is 0. 83 by NREL PVWatts v8 default — or 0. 77 if you want a conservative.