How is solar panel output estimated?

Panel wattage multiplied by average daily sunlight hours and system efficiency.

Why does location significantly affect output?

Average sunlight hours vary by latitude, climate, and local weather.

Does panel angle and orientation matter?

Yes significantly — proper positioning maximizes direct sun exposure and output.

Solar Panel Energy Output Calculator

Estimate how much electricity your solar panel system will generate per day, month, and year based on your location's sun exposure.

How Solar Panel Output Is Estimated

A solar system's real-world energy output depends on its total rated wattage, the average number of "peak sun hours" its location receives per day (a measure of solar irradiance, not daylight hours), and a system efficiency or "derate" factor that accounts for real-world losses from inverter conversion, wiring, temperature, dust, and panel angle.

How to Use This Calculator

Enter the wattage rating of a single panel and how many panels are in your system.
Enter your location's average peak sun hours per day — this varies by region and season, and solar resource maps (like NREL's) provide typical local averages.
Enter a system efficiency factor; 75–80% is a commonly used real-world default that accounts for inverter and system losses.

The Formula Used

Total System Size (kW) = (Panel Wattage × Number of Panels) ÷ 1000. Daily Output (kWh) = System Size (kW) × Peak Sun Hours × (Efficiency % ÷ 100). Monthly Output = Daily Output × 30. Yearly Output = Daily Output × 365.

Worked Example

A system with 20 panels rated at 400W each has a total size of 8 kW. In a location averaging 5 peak sun hours per day with 80% system efficiency, daily output is 8 × 5 × 0.80 = 32 kWh/day, or about 960 kWh/month and roughly 11,680 kWh/year.

Using This Estimate

Compare the estimated yearly output to your household's annual electricity usage (visible on your utility bills) to gauge roughly what percentage of your energy needs the system could offset. Actual output varies with weather, shading, panel degradation over time, and seasonal changes in sun hours, so treat this as a planning estimate rather than a guaranteed production figure.