Most residential panels in 2025 are rated 250–550 watts, with 400-watt models becoming the new standard. A 400-watt panel can generate roughly 1. 5 kWh of energy per day, depending on local sunlight. household's 900 kWh/month. For 1 kWh per day, you would need about a 300-watt solar panel. If we know both the solar panel size and peak sun hours at our location, we can calculate how many kilowatts does a solar panel produce per day using this equation: Daily kWh. Think of it as the speed at which energy is being used. It's an instantaneous measurement. Panel wattage is related to potential output over time; for example, a 400-watt solar panel could potentially generate 400 watt-hours of power in one hour of direct sunlight. 1 kilowatt (kW) is equal to 1,000.