Free online solar panel output calculator — estimate daily, monthly, and yearly kWh energy production based on panel wattage, number of panels, sun hours, and system efficiency. Losses come from inverter efficiency, wiring, temperature, and dirt. Generally, a standard solar panel produces about 250 to 350 watts of power. How Much Sun Do You Get (Peak Sun Hours). In real life, output can be a bit lower. Think of it like a car's fuel rating it shows potential, not. An off-grid solar system's size depends on factors such as your daily energy consumption, local sunlight availability, chosen equipment, the appliances that you're trying to run, and system configuration. Below is a combination of multiple calculators that consider these variables and allow you to. 25.