System Size (kWdc) Enter the rated DC capacity of your solar array (e.g., 5.0 for a 5 kW system)

Location Annual Solar Irradiance (kWh/m²/day) Enter average daily solar radiation for your location (e.g., 5.5 for moderate sun areas)

DC to AC Derate Factor (ratio) Enter system efficiency factor (typical range 0.77 to 0.85)

Array Tilt (degrees) Enter the tilt angle of your solar panels from horizontal (0-90 degrees)

Array Azimuth (degrees) Enter compass direction panels face (180 = south, 90 = east, 270 = west)

Quick Examples:

5 kW Residential System 10 kW Commercial System

Calculate Clear

This calculator is for informational purposes only. Results are estimates based on simplified models and may vary from actual system performance. Consult a qualified solar installer for precise system sizing and production estimates.

What Is Annual Energy Production

Annual Energy Production is the total amount of electricity a solar panel system generates in one year. It is measured in kilowatt-hours (kWh). This number helps you understand how much power your solar array can produce. The value depends on your system size, location, panel angle, and system efficiency. Knowing this number helps you plan your solar investment and estimate savings on electric bills.

How Annual Energy Production Is Calculated

Formula

The calculation starts by converting daily solar irradiance to yearly irradiance. This is done by multiplying the daily value by 365 days. Next, the formula applies the derate factor to account for real-world losses like inverter efficiency and wiring. The orientation factor adjusts for how your panels are tilted and which direction they face. Finally, all these values are multiplied together with your system size to give the estimated annual energy output in kilowatt-hours.

Why Annual Energy Production Matters

Knowing your estimated annual energy production helps you make informed decisions about solar investments. This number tells you how much electricity your system can generate and helps you estimate potential savings on utility bills.

Why Energy Estimation Is Important for Solar Planning

Without accurate energy estimates, you may install a system that is too small or too large for your needs. An undersized system will not offset enough of your electricity usage. An oversized system costs more than necessary and may produce excess power you cannot use. Getting this estimate right helps you size your system correctly and understand your return on investment.

For Homeowners

Homeowners can use this estimate to understand how much of their electricity bill a solar system might offset. A typical 5 kW system in a moderate climate may produce 6,000 to 8,000 kWh per year. Compare this number to your annual electricity usage from utility bills to see potential savings.

For Commercial Property Owners

Commercial properties often have larger electricity demands and bigger roof spaces. A 50 kW commercial system may produce 60,000 to 80,000 kWh per year depending on location. This helps businesses plan for energy cost reduction and sustainability goals. Larger systems may also qualify for different incentive programs.

Annual Energy Production vs Rated Capacity

Rated capacity tells you the maximum power output under ideal test conditions. Annual energy production tells you actual expected output over a year. A 10 kW system in Arizona produces more energy than the same system in Seattle because of different solar irradiance levels. Always consider energy production, not just rated capacity, when comparing solar options.

Example Calculation

Consider a homeowner planning a 5 kW solar system in a location with moderate sunshine. The system size is 5 kWdc, the local solar irradiance is 5.5 kWh/m²/day, the derate factor is 0.77, the panels are tilted at 25 degrees, and they face south at 180 degrees azimuth.

The calculator first converts daily irradiance to annual: 5.5 × 365 = 2,007.5 kWh/m²/year. Then it calculates the orientation factor based on tilt and azimuth. For a south-facing system at 25 degrees tilt, the orientation factor is close to 1.0. The formula then multiplies: 5 × 5.5 × 365 × 0.77 × 0.996 = 7,693 kWh per year.

The estimated annual energy production is 7,693 kWh per year. The average monthly production is about 641 kWh. The capacity factor is approximately 17.6 percent.

This means the 5 kW system would generate about 7,693 kWh of electricity each year under typical conditions. If the homeowner uses 10,000 kWh per year, this system could offset roughly 77 percent of their electricity usage. They may want to consider a larger system or energy efficiency improvements to cover more of their usage.

Frequently Asked Questions

Who is this Solar PVWatts Calculator for?

This calculator is for homeowners, business owners, and solar professionals who want to estimate energy production for photovoltaic systems. It works best for fixed-tilt grid-connected systems. Use it during the planning phase to compare different system sizes and configurations.

How do I find the solar irradiance for my location?

Solar irradiance data is available from the National Renewable Energy Laboratory (NREL) and other solar resource websites. Values in the US typically range from 3.5 kWh/m²/day in cloudy areas to 7.0 kWh/m²/day in desert regions. Local solar installers can also provide this information.

What derate factor should I use?

Most residential systems use a derate factor between 0.77 and 0.85. The PVWatts default is 0.77, which accounts for typical inverter losses, wiring losses, soiling, and temperature effects. High-quality equipment may achieve higher values. Consult your installer for system-specific estimates.

Can I use this calculator for tracking systems?

This calculator is designed for fixed-tilt systems and may not accurately estimate production for single-axis or dual-axis tracking systems. Tracking systems typically produce 15 to 25 percent more energy than fixed systems. Consult a solar professional for tracking system estimates.

Does this calculator account for shading?

This calculator does not account for shading from trees, buildings, or other obstacles. Shading can significantly reduce actual energy production. A professional solar site assessment includes shading analysis for more accurate estimates.