A 280W Solar Panel refers to a photovoltaic panel with a rated power output of 280 watts under optimal conditions. This wattage indicates how much power the panel can theoretically produce in one hour of peak sunlight. . In California and Texas, where we have the most solar panels installed, we get 5. 92 peak sun hours per day, respectively. Quick outtake from the calculator and chart: For 1 kWh per day, you would need about a 300-watt solar panel., averages range from 3 hours (Alaska) to 7 hours (Arizona). Calculate daily kWh output with this equation: 0. Formula used: Daily kWh = (Panel Wp × Number of panels × Peak Sun Hours × (1 − derate)) ÷ 1000. Default derate is the percentage losses (inverter, wiring, temperature. . The Solar Panel Output Calculator is a highly useful tool so you can understand the total output, production, or power generation from your solar panels per day, month, or year. Input your solar panel system's total size and the peak sun hours specific to your location, this calculator simplifies. . Scenario: A homeowner installs a 5 kW solar system in a region with 4 peak sun hours and 85% system efficiency.