Solar Panel Wattage Calculator by Omni

Enter the total area of the solar panels in square feet.
Enter the efficiency of the solar panels (as a percentage).
Enter the average solar irradiance in watts per square meter.

Solar Panel Wattage Calculation Chart

FactorValueUnit
Panel Size1.6
Solar Irradiance1000W/m²
Panel Efficiency20%
Temperature Coefficient-0.4%per °C
Standard Test Conditions25°C
Actual Temperature35°C
Temperature Difference10°C
Temperature Loss4%
Theoretical Wattage320W
Actual Wattage307.2W

Solar Panel Wattage Calculation Formula

The formula for calculating solar panel wattage is:

W = A × r × η × [1 - α(T - 25)]

Where:

  • W is the wattage output
  • A is the panel area in m²
  • r is the solar irradiance in W/m²
  • η (eta) is the panel efficiency
  • α (alpha) is the temperature coefficient
  • T is the actual panel temperature in °C

Using the values from our table:

W = 1.6 × 1000 × 0.20 × [1 - 0.004(35 - 25)] = 320 × 0.96 = 307.2 W

How do you calculate solar panel wattage?

Here’s a detailed explanation of the process:

Determine panel size: Measure the panel’s dimensions to calculate its area in square meters.

Identify solar irradiance: Use the standard solar irradiance value of 1000 W/m² for comparison purposes.

Check panel efficiency: Find the manufacturer-specified efficiency rating, typically between 15-22% for modern panels.

Consider temperature effects:

  • Note the panel’s temperature coefficient (usually -0.3% to -0.5% per °C above 25°C)
  • Measure or estimate the actual panel temperature
  • Calculate temperature-related efficiency loss

Apply the formula: Use the equation W = A × r × η × [1 – α(T – 25)]

Let’s use a 1.6 m² panel with 20% efficiency and a -0.4% per °C temperature coefficient, operating at 35°C:

  1. Panel area (A) = 1.6 m²
  2. Solar irradiance (r) = 1000 W/m²
  3. Panel efficiency (η) = 20% = 0.20
  4. Temperature coefficient (α) = -0.4% = -0.004
  5. Actual temperature (T) = 35°C
Theoretical wattage (at 25°C): W = 1.6 × 1000 × 0.20 = 320 W
Actual wattage (at 35°C): W = 1.6 × 1000 × 0.20 × [1 - 0.004(35 - 25)] = 320 × 0.96 = 307.2 W

This calculation shows that the panel’s actual output (307.2 W) is lower than its rated output (320 W) due to temperature-related efficiency losses.

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