Estimating the daily energy production of a 300 Watt solar panel in your location and for different months can be done using a simple formula: Daily Energy Production (Watt-hours) = Power Rating of the solar panel (Watts) x Daily Peak Sun Hours in your locationEstimating the daily energy production of a 300 Watt solar panel in your location and for different months can be done using a simple formula: Daily Energy Production (Watt-hours) = Power Rating of the solar panel (Watts) x Daily Peak Sun Hours in your locationTo calculate solar panel output per day (in kWh), we need to check only 3 factors: Solar panel's maximum power rating. That's the wattage; we have 100W, 200W, 300W solar panels, and so on. How much solar energy do you get in your area? That is determined by average peak solar hours. South. The wattage rating of a panel (for example, 400W) represents its power output under ideal test conditions — but actual daily energy production depends on sunlight hours, efficiency, and installation setup. How to Calculate Solar Energy Output The basic formula to estimate solar output is: Daily. Under ideal sunlight conditions, a 300 Watt solar panel has the potential to produce 300 Watts (0. 3 kW) of power, or even a little bit more., 100W or 400W) indicates the maximum amount of electricity a PV panel can generate per hour, many factors come into play that affect how much power output you'll actually get. Formula: Solar panel output = (Solar Panel rated wattage ×.