Average Sun Hours Calculator

Calculator Inputs

Use daily peak sun hours for each month. Then refine the result with collection and operating factors.

Monthly Daily Sun Hours

January (h/day)

February (h/day)

March (h/day)

April (h/day)

May (h/day)

June (h/day)

July (h/day)

August (h/day)

September (h/day)

October (h/day)

November (h/day)

December (h/day)

Adjustment and Yield Factors

Tilt Factor (%)

Orientation Factor (%)

Tracking Gain (%)

Shading Loss (%)

Soiling Loss (%)

Climate Reserve (%)

System Availability (%)

Performance Ratio (%)

Input Tips

Use monthly peak sun hours or daily irradiation equivalents. Keep factors near 100% for neutral assumptions. Reduce losses only when measured site data supports them.

Reset

Example Data Table

This sample dataset can be loaded into the calculator using the example button.

Month	Example Sun Hours (h/day)	Days	Monthly Equivalent Hours
January	3.90	31	120.90
February	4.60	28	128.80
March	5.40	31	167.40
April	6.20	30	186.00
May	6.80	31	210.80
June	6.60	30	198.00
July	6.10	31	189.10
August	5.90	31	182.90
September	5.60	30	168.00
October	5.10	31	158.10
November	4.30	30	129.00
December	3.70	31	114.70

Formula Used

1) Weighted Average Sun Hours
ASH = Σ(H_m × D_m) ÷ 365

2) Effective Sun Hours
ESH = ASH × F_tilt × F_orientation × F_availability × (1 − L_shade) × (1 − L_soil) × (1 − L_climate) × (1 + G_tracking)

3) Annual Solar Input
Annual Solar Input = Σ(H_m × D_m)

4) Estimated Annual Yield per kW
Yield per kW = Adjusted Annual Solar Input × Performance Ratio

Here, H_m is the monthly daily peak sun hours and D_m is the number of days in each month. Factors are entered as percentages and converted into multipliers during calculation.

How to Use This Calculator

Enter daily peak sun hours for all twelve months.
Set tilt and orientation factors based on your array alignment.
Apply tracking gain only if the system actually tracks the sun.
Add realistic shading, soiling, reserve, and availability assumptions.
Enter a performance ratio to estimate yearly output per installed kW.
Press the calculate button to display results above the form.
Review summary cards, tables, and the monthly Plotly graph.
Export the finished analysis to CSV or PDF.

Frequently Asked Questions

1) What are average sun hours?

They represent peak sun hours, which convert daily solar irradiation into equivalent full-intensity sunlight hours. They help compare solar resource levels across months and sites.

2) Why is the average weighted by days?

Months have different lengths. Weighting by actual days produces a more realistic annual average than taking a simple twelve-month arithmetic mean.

3) What does the tilt factor do?

It adjusts collected sunlight for panel tilt quality. A well-optimized tilt stays near 100%, while suboptimal positioning lowers effective collection hours.

4) Should performance ratio change sun hours?

No. Performance ratio affects output yield, not the site solar resource itself. The calculator keeps sun hours and energy yield as separate results.

5) What is climate reserve?

It is a planning margin for uncertainty, weather anomalies, or conservative forecasting. Larger reserves lower the effective sun hours used for design decisions.

6) Why can adjusted values exceed raw values?

They can rise only when tracking gain outweighs losses. For fixed systems without gains, adjusted values usually remain below the raw solar resource.

7) Can I use irradiation data instead of measured sunlight hours?

Yes. Daily irradiation in kWh/m²/day is numerically equivalent to peak sun hours, so it can be entered directly for each month.

8) What is the estimated yield per kW result?

It is a planning estimate of yearly kilowatt-hours from one installed kilowatt of solar capacity, based on adjusted solar input and performance ratio.