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Solar Panel Energy Calculator

Calculate the daily and annual energy output of a solar panel system based on panel wattage, sun hours, efficiency, and number of panels.

Reviewed by Christopher FloiedPublished Updated

This free online solar panel energy calculator provides instant results with no signup required. All calculations run directly in your browser — your data is never sent to a server. Enter your values below and see results update in real time as you type. Perfect for everyday calculations, homework, or professional use.

Range: 1 – 1000

Unit: W

Rated wattage of each solar panel (STC)

Range: 0.5 – 12

Unit: hours/day

Average peak sun hours per day for your location

Range: 1 – 100

Unit: %

Overall system efficiency (typically 75-85%, accounts for inverter losses, wiring, soiling)

Range: 1 – 500

Total number of solar panels in the system

Results

Daily Energy Output

16 kWh/day

Annual Energy Output

5840 kWh/year

How to Use This Calculator

1

Enter your input values

Fill in all required input fields for the Solar Panel Energy Calculator. Most fields include unit selectors so you can work in your preferred unit system — metric or imperial, whichever matches your problem.

2

Review your inputs

Double-check that all values are correct and that you have selected the right units for each field. Incorrect units are the most common source of calculation errors and can produce results that are off by factors of 2, 10, or more.

3

Read the results

The Solar Panel Energy Calculator instantly computes the output and displays results with units clearly labeled. All calculations happen in your browser — no loading time and no data sent to a server.

4

Explore parameter sensitivity

Try adjusting individual input values to see how the output changes. This is a quick and effective way to develop intuition about how different parameters influence the result and to identify which inputs have the largest effect.

When to Use This Calculator

  • •Use the Solar Panel Energy Calculator when you need accurate results quickly without the risk of manual computation errors or unit conversion mistakes.
  • •Use it to verify calculations made by hand or in spreadsheets — an independent check can catch errors before they lead to costly decisions.
  • •Use it to explore how changing input parameters affects the output — a quick way to develop intuition and identify the most influential variables.
  • •Use it when collaborating with others to ensure everyone is working from the same numbers and applying the same assumptions.

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About Solar Panel Energy Calculator

The Solar Panel Energy Calculator estimates how much electricity a photovoltaic system will produce based on the panel specifications and local sunlight conditions. Solar energy is the fastest-growing source of renewable electricity worldwide, and understanding potential output is essential for system sizing, financial planning, and comparing quotes from installers. This calculator takes into account the rated wattage of each panel, the average peak sun hours at your location, the overall system efficiency (which includes losses from the inverter, wiring, temperature, and soiling), and the total number of panels. The result gives you both daily and annual energy production in kilowatt-hours, allowing you to estimate savings on your electricity bill and your contribution to reducing fossil fuel consumption.

The Math Behind It

Solar panels convert sunlight into direct current (DC) electricity through the photovoltaic effect. Each panel has a rated wattage measured under Standard Test Conditions (STC): 1,000 W/m2 irradiance, 25 degrees C cell temperature, and air mass 1.5 spectrum. Real-world output is lower than the STC rating because conditions are rarely ideal. Peak sun hours (PSH) represent the equivalent number of hours per day when solar irradiance averages 1,000 W/m2. A location receiving 5 PSH gets the same total energy as 5 hours of full-intensity sunshine. PSH varies by latitude, season, weather, and panel orientation. Databases like PVGIS and NREL's Solar Resource Data provide location-specific values. System efficiency accounts for all losses between the panels and the grid or battery. Typical losses include inverter conversion (3-6%), wiring resistance (1-3%), module mismatch (1-2%), soiling and dust (2-5%), and temperature derating (5-15% in hot climates). A combined efficiency of 75-85% is common for well-designed residential systems. The annual output is simply the daily output multiplied by 365. For more precise estimates, monthly PSH values should be used since winter months may produce 30-50% less than summer months at mid-latitudes. Panel degradation of about 0.5% per year should also be considered for long-term projections. Oversizing the system slightly beyond your consumption is often recommended to account for degradation and to build credit during high-production months that offsets lower winter output.

Formula Reference

Solar Energy Output

E = (watts * sunHours * efficiency * panels) / 1000

Variables: watts = rated panel power in W, sunHours = peak sun hours per day, efficiency = system efficiency as decimal, panels = number of panels

Worked Examples

Example 1: Residential 10-Panel System

A homeowner installs 10 panels rated at 400W each in a location with 5 peak sun hours and 80% system efficiency.

Step 1:Daily output = (400 * 5 * 0.80 * 10) / 1000 = 16.0 kWh/day
Step 2:Annual output = 16.0 * 365 = 5,840 kWh/year

The system produces approximately 16.0 kWh per day or 5,840 kWh per year.

Example 2: Small Off-Grid Cabin

A cabin uses 4 panels of 300W each with 3.5 peak sun hours and 75% efficiency.

Step 1:Daily output = (300 * 3.5 * 0.75 * 4) / 1000 = 3.15 kWh/day
Step 2:Annual output = 3.15 * 365 = 1,149.75 kWh/year

The system produces approximately 3.15 kWh per day or 1,150 kWh per year.

Example 3: Commercial Rooftop Array

A business installs 100 panels of 450W each in a sunny region with 6.5 PSH and 82% efficiency.

Step 1:Daily output = (450 * 6.5 * 0.82 * 100) / 1000 = 239.85 kWh/day
Step 2:Annual output = 239.85 * 365 = 87,545.25 kWh/year

The system produces approximately 239.9 kWh per day or 87,545 kWh per year.

Common Mistakes & Tips

  • !Using the STC rating as actual output without applying efficiency derating, which overestimates production by 15-25%.
  • !Confusing peak sun hours with total daylight hours. A location with 12 hours of daylight may only have 4-5 peak sun hours.
  • !Forgetting to divide by 1000 to convert watt-hours to kilowatt-hours, resulting in values 1000 times too large.
  • !Ignoring seasonal variation by using summer peak sun hours year-round, which inflates the annual estimate.

Related Concepts

Wind Turbine Power

Calculates the power output of a wind turbine based on rotor size and wind speed, another key renewable energy technology.

Peak Sun Hours

A measure of solar resource availability that expresses the total daily irradiance as equivalent hours at 1,000 W/m2 intensity.

Used in These Calculators

Calculators that build on or apply the concepts from this page:

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Frequently Asked Questions

What are peak sun hours and how do I find them for my area?

Peak sun hours represent the equivalent hours of 1,000 W/m2 sunlight per day. Use NREL's PVWatts or the EU PVGIS tool to find values for your exact location and roof orientation.

Why is system efficiency less than 100%?

Losses occur in the inverter (DC to AC conversion), wiring, module mismatch, dust accumulation, and temperature effects. Combined, these typically reduce output to 75-85% of the theoretical maximum.

How does panel degradation affect long-term output?

Most panels degrade at about 0.5% per year. After 25 years, output is typically around 87% of the original rated capacity. Manufacturers usually guarantee at least 80% output after 25 years.

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