The "220W" in a solar panel refers to its maximum power output under standard testing conditions, which typically include direct sunlight at an intensity of 1000 watts per square meter and a cell temperature of 25°C (77°F). Sunlight Exposure: The amount of sunlight a panel receives directly affects its output. Losses come from inverter efficiency, wiring, temperature, and dirt. Compared to lower wattage panels, a 220W panel offers a decent balance between cost and output. These factors determine how much electricity your solar system generates daily, impacting: At higher latitudes or during winter months, peak sun hours decrease, affecting daily production. Accurate Solar Production Formula:. To calculate solar panel output per day (in kWh), we need to check only 3 factors: Solar panel's maximum power rating.