Solar Panel Calculator
Estimate solar panel output and savings. Add usage and rates to estimate energy costs or output.
System Details
Environment & Losses
Energy and environment guide · Solar panel output estimate
About Solar Panel Output Calculator
Estimate daily, monthly, and annual energy from panel wattage, panel count, peak sun hours, and a system-efficiency percentage. It also reports the array's nominal power size in kilowatts.
This calculator estimates energy from panel rating, panel count, peak sun hours, and a system-efficiency percentage. It gives a simple daily, monthly, and annual projection from those assumptions, not a site survey or a production guarantee.
How to Use This Tool
- 1.Enter the rated wattage of one panel and the number of panels.
- 2.Enter peak sun hours per day for the location and an estimated system efficiency.
- 3.Calculate and inspect the output estimates. Use local solar data and site conditions for a project quote.
Technical Details and Assumptions
1.Array size is nominal DC power
Panel wattage multiplied by quantity gives the array's rated wattage. Dividing by 1,000 expresses that nominal size in kilowatts; it is not the same as energy produced over time.
2.Sun hours represent equivalent full-sun time
Peak sun hours are a way to express the solar energy available over a day as equivalent hours at a reference irradiance. They are not simply the number of daylight hours.
3.Efficiency reduces the theoretical output
The tool multiplies rated power by peak sun hours and the entered efficiency percentage. The monthly figure uses a 30-day estimate and the annual figure uses 365 days.
4.Location and system conditions matter
Season, roof direction, shading, temperature, inverter limits, dirt, and downtime affect actual production. Use local solar data and system specifications to refine an estimate.
How the Calculation Works
Array wattage = panel rating × quantity. Estimated daily Wh = array watts × peak sun hours × efficiency fraction. The page divides by 1,000 for kWh, then scales daily output by 30 days and 365 days for monthly and annual estimates.
Worked Example
Ten 400 W panels form a 4 kW array. At five peak sun hours and 75% efficiency, the simplified daily estimate is 15 kWh.
Where This Tool Can Help
Compare a rough array output across panel count, rated power, sun hours, or system-loss assumptions.
Sizing a first-pass array
Estimate the nominal panel capacity and energy yield before comparing it with a household or project demand profile.
Comparing panel counts
Change the number or rated wattage of panels to see the proportional change under the same sun-hour and efficiency assumptions.
Checking a vendor estimate
Use the result as a simple cross-check, then compare assumptions with the proposal's location, tilt, shading, inverter, and loss estimates.
Exploring seasonal output
Run separate estimates with seasonal peak sun hours to understand why output can change through the year.
Tips for a Useful Estimate
- Use the panel's rated wattage and a local peak-sun-hours estimate for the installation location.
- Enter efficiency as a percentage, such as 75 for 75%, and avoid counting the same losses twice.
- Use the monthly and annual results as average projections based on 30 and 365 days, not as guaranteed meter readings.
- Check shading, orientation, inverter capacity, and grid or battery limits with the system design.
Limitations and Review
Actual generation depends on location, season, roof angle, shading, temperature, inverter, wiring, degradation, and utility curtailment. Peak sun hours are not total daylight hours. This estimate does not size a system or guarantee bill savings; use a site-specific assessment.
The page calculates array watts = panel watts × panel count, daily Wh = array watts × peak sun hours × efficiency fraction, daily kWh = daily Wh ÷ 1,000, monthly kWh = daily kWh × 30, and annual kWh = daily kWh × 365.
Frequently Asked Questions
What are peak sun hours?
They represent equivalent hours at a reference solar intensity, not simply daylight duration.
Why enter efficiency below 100%?
Real systems lose energy through conversion, temperature, wiring, and other effects.
Does this estimate include battery storage?
No. It estimates panel energy output only.
Are peak sun hours the same as daylight hours?
No. They represent equivalent full-output sun exposure, not the total time between sunrise and sunset.
Will my panels produce this exact amount?
No. The result is an estimate; weather, location, orientation, shading, temperature, and system losses change real output.