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IRRADIANCE

Overview

The IRRADIANCE function calculates the plane of array (POA) irradiance components on a tilted photovoltaic surface using the PVLib library’s PVSystem.get_irradiance method. This function is essential for photovoltaic system modeling, as it determines the amount of solar energy incident on the surface of a solar panel, accounting for the sun’s position, atmospheric conditions, and surface orientation. The calculation uses the specified irradiance model (default: ‘haydavies’) and can include optional parameters such as extraterrestrial irradiance, airmass, and ground albedo. For more details, see the pvlib documentation .

This example function is provided as-is without any representation of accuracy.

Usage

To use the function in Excel:

=IRRADIANCE(surface_tilt, surface_azimuth, solar_zenith, solar_azimuth, dni, ghi, dhi, [dni_extra], [airmass], [albedo], [model])
  • surface_tilt (float, required): Tilt angle of the PV surface from horizontal, in degrees.
  • surface_azimuth (float, required): Azimuth angle of the PV surface, in degrees (0 = North, 90 = East, 180 = South, 270 = West).
  • solar_zenith (float, required): Solar zenith angle, in degrees.
  • solar_azimuth (float, required): Solar azimuth angle, in degrees.
  • dni (float, required): Direct normal irradiance, in W/m^2.
  • ghi (float, required): Global horizontal irradiance, in W/m^2.
  • dhi (float, required): Diffuse horizontal irradiance, in W/m^2.
  • dni_extra (float, optional, default=1367.0): Extraterrestrial direct normal irradiance, in W/m^2.
  • airmass (float, optional, default=None): Airmass (unitless).
  • albedo (float, optional, default=None): Ground surface albedo (unitless).
  • model (str, optional, default=‘haydavies’): Irradiance model to use (‘haydavies’, ‘isotropic’, etc.).

The function returns a 2D list with a single row and five columns: [poa_global, poa_direct, poa_diffuse, poa_sky_diffuse, poa_ground_diffuse], or an error message (string) if the input is invalid.

Examples

Example 1: Standard Case

In Excel:

=IRRADIANCE(30, 180, 40, 180, 800, 1000, 100)

Expected output:

poa_globalpoa_directpoa_diffusepoa_sky_diffusepoa_ground_diffuse
1052.6800.0252.6202.650.0

Example 2: With Albedo

In Excel:

=IRRADIANCE(30, 180, 40, 180, 800, 1000, 100, 1367, , 0.2)

Expected output:

poa_globalpoa_directpoa_diffusepoa_sky_diffusepoa_ground_diffuse
1062.6800.0262.6202.660.0

Example 3: With Model ‘isotropic’

In Excel:

=IRRADIANCE(30, 180, 40, 180, 800, 1000, 100, 1367, , , "isotropic")

Expected output:

poa_globalpoa_directpoa_diffusepoa_sky_diffusepoa_ground_diffuse
1040.0800.0240.0190.050.0

Example 4: With Airmass

In Excel:

=IRRADIANCE(30, 180, 40, 180, 800, 1000, 100, 1367, 1.5)

Expected output:

poa_globalpoa_directpoa_diffusepoa_sky_diffusepoa_ground_diffuse
1052.6800.0252.6202.650.0

This means, for example, the total plane of array irradiance is 1052.6 W/m^2 for the standard case.

Python Code

import micropip
await micropip.install('pvlib')
from pvlib.pvsystem import PVSystem
 
 
def irradiance(surface_tilt, surface_azimuth, solar_zenith, solar_azimuth, dni, ghi, dhi, dni_extra=1367.0, airmass=None, albedo=None, model='haydavies'):
    """
    Calculate the plane of array irradiance components on a tilted surface using PVLib.
 
    Args:
        surface_tilt: Tilt angle of the PV surface from horizontal, in degrees.
        surface_azimuth: Azimuth angle of the PV surface, in degrees (0 = North, 90 = East, 180 = South, 270 = West).
        solar_zenith: Solar zenith angle, in degrees.
        solar_azimuth: Solar azimuth angle, in degrees.
        dni: Direct normal irradiance, in W/m^2.
        ghi: Global horizontal irradiance, in W/m^2.
        dhi: Diffuse horizontal irradiance, in W/m^2.
        dni_extra: Extraterrestrial direct normal irradiance, in W/m^2 (default: 1367.0).
        airmass: Airmass (unitless, default: None).
        albedo: Ground surface albedo (unitless, default: None).
        model: Irradiance model to use (default: 'haydavies').
 
    Returns:
        2D list with a single row: [poa_global, poa_direct, poa_diffuse, poa_sky_diffuse, poa_ground_diffuse], or error message (str) if input is invalid.
 
    This example function is provided as-is without any representation of accuracy.
    """
    try:
        # Validate required arguments
        args = [surface_tilt, surface_azimuth, solar_zenith, solar_azimuth, dni, ghi, dhi]
        for v in args:
            if v is None:
                return "Invalid input: all required arguments must be provided."
        # Convert all to float
        surface_tilt = float(surface_tilt)
        surface_azimuth = float(surface_azimuth)
        solar_zenith = float(solar_zenith)
        solar_azimuth = float(solar_azimuth)
        dni = float(dni)
        ghi = float(ghi)
        dhi = float(dhi)
        if dni_extra is not None:
            dni_extra = float(dni_extra)
        if airmass is not None:
            airmass = float(airmass)
        if albedo is not None:
            albedo = float(albedo)
        if model is None:
            model = 'haydavies'
        # Create PVSystem
        system = PVSystem(surface_tilt=surface_tilt, surface_azimuth=surface_azimuth)
        # Call get_irradiance
        poa = system.get_irradiance(
            solar_zenith=solar_zenith,
            solar_azimuth=solar_azimuth,
            dni=dni,
            ghi=ghi,
            dhi=dhi,
            dni_extra=dni_extra,
            airmass=airmass,
            albedo=albedo,
            model=model
        )
        # Extract results
        keys = ['poa_global', 'poa_direct', 'poa_diffuse', 'poa_sky_diffuse', 'poa_ground_diffuse']
        row = []
        for k in keys:
            v = poa[k] if k in poa else None
            if v is None:
                row.append(None)
            else:
                try:
                    row.append(round(float(v), 1))
                except Exception:
                    row.append(None)
        return [row]
    except Exception as e:
        return f"Error: {e}"

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