SOLARPOSITION

This function computes solar position angles for one or more timestamps at a specified site.

For each timestamp, it returns azimuth, elevation, and apparent zenith using one of pvlib’s solar-position algorithms.

Elevation and zenith are related by:

\mathrm{elevation} = 90^\circ - \mathrm{zenith}

Apparent zenith includes atmospheric refraction and is commonly preferred over true zenith for irradiance modeling.

Excel Usage

=SOLARPOSITION(time, latitude, longitude, altitude, pressure, solarpos_meth, temperature)
  • time (list[list], required): Timestamp or 2D range of timestamps in ISO8601 format.
  • latitude (float, required): Latitude north of equator (deg).
  • longitude (float, required): Longitude east of prime meridian (deg).
  • altitude (float, optional, default: 0): Site elevation above sea level (m).
  • pressure (float, optional, default: 101325): Atmospheric pressure (Pa).
  • solarpos_meth (str, optional, default: “nrel_numpy”): Solar position algorithm method.
  • temperature (float, optional, default: 12): Ambient temperature used in refraction calculation (deg C).

Returns (list[list]): 2D list with one row per timestamp containing azimuth, elevation, and apparent zenith in degrees, or an error string.

Example 1: Summer midday position at sea level

Inputs:

time latitude longitude altitude pressure solarpos_meth temperature
2024-06-20T12:00:00Z 35 -120 0 101325 nrel_numpy 12

Excel formula:

=SOLARPOSITION("2024-06-20T12:00:00Z", 35, -120, 0, 101325, "nrel_numpy", 12)

Expected output:

Result
53.1775 -8.77273 98.7727
Example 2: Summer morning position at sea level

Inputs:

time latitude longitude altitude pressure solarpos_meth temperature
2024-06-20T06:00:00Z 35 -120 0 101325 nrel_numpy 12

Excel formula:

=SOLARPOSITION("2024-06-20T06:00:00Z", 35, -120, 0, 101325, "nrel_numpy", 12)

Expected output:

Result
329.216 -24.8381 114.838
Example 3: Winter midday position at higher altitude

Inputs:

time latitude longitude altitude pressure solarpos_meth temperature
2024-12-21T12:00:00Z 35 -120 100 90000 nrel_numpy 12

Excel formula:

=SOLARPOSITION("2024-12-21T12:00:00Z", 35, -120, 100, 90000, "nrel_numpy", 12)

Expected output:

Result
94.7359 -36.8049 126.805
Example 4: Row vector of timestamps

Inputs:

time latitude longitude altitude pressure solarpos_meth temperature
2024-06-20T12:00:00Z 2024-06-20T18:00:00Z 35 -120 0 101325 nrel_numpy 12

Excel formula:

=SOLARPOSITION({"2024-06-20T12:00:00Z","2024-06-20T18:00:00Z"}, 35, -120, 0, 101325, "nrel_numpy", 12)

Expected output:

Result
53.1775 -8.77273 98.7727
105.383 61.176 28.8148
Example 5: Winter morning position at sea level

Inputs:

time latitude longitude altitude pressure solarpos_meth temperature
2024-12-21T09:00:00Z 35 -120 0 101325 nrel_numpy 12

Excel formula:

=SOLARPOSITION("2024-12-21T09:00:00Z", 35, -120, 0, 101325, "nrel_numpy", 12)

Expected output:

Result
53.4021 -72.2847 162.285

Python Code

Show Code 
import pandas as pd
from pvlib.solarposition import get_solarposition as pvlib_get_solarposition

def solarposition(time, latitude, longitude, altitude=0, pressure=101325, solarpos_meth='nrel_numpy', temperature=12):
    """
    Calculate solar azimuth, elevation, and apparent zenith for given times and location.

    See: https://pvlib-python.readthedocs.io/en/stable/reference/generated/pvlib.solarposition.get_solarposition.html

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

    Args:
        time (list[list]): Timestamp or 2D range of timestamps in ISO8601 format.
        latitude (float): Latitude north of equator (deg).
        longitude (float): Longitude east of prime meridian (deg).
        altitude (float, optional): Site elevation above sea level (m). Default is 0.
        pressure (float, optional): Atmospheric pressure (Pa). Default is 101325.
        solarpos_meth (str, optional): Solar position algorithm method. Valid options: NREL NumPy, NREL Numba, PyEphem, Ephemeris, NREL C. Default is 'nrel_numpy'.
        temperature (float, optional): Ambient temperature used in refraction calculation (deg C). Default is 12.

    Returns:
        list[list]: 2D list with one row per timestamp containing azimuth, elevation, and apparent zenith in degrees, or an error string.
    """
    try:
      def flatten_str(data):
        if not isinstance(data, list):
          return [str(data)]

        flat = []
        for row in data:
          row = row if isinstance(row, list) else [row]
          for value in row:
            if value == "":
              continue
            flat.append(str(value))
        return flat

      times = flatten_str(time)
      if len(times) == 0:
        return "Error: time array cannot be empty"

      dt_index = pd.DatetimeIndex(times)

      lat = float(latitude)
      lon = float(longitude)
      alt = float(altitude)
      pres = float(pressure)
      temp = float(temperature)
      meth = str(solarpos_meth)

      valid_methods = ['nrel_numpy', 'nrel_numba', 'pyephem', 'ephemeris', 'nrel_c']
      if meth not in valid_methods:
        return "Error: solarpos_meth must be one of nrel_numpy, nrel_numba, pyephem, ephemeris, nrel_c"

      df = pvlib_get_solarposition(
        time=dt_index,
        latitude=lat,
        longitude=lon,
        altitude=alt,
        pressure=pres,
        method=meth,
        temperature=temp
      )

      result = []
      for i in range(len(dt_index)):
        az = float(df.iloc[i]["azimuth"])
        el = float(df.iloc[i]["elevation"])
        zen = float(df.iloc[i]["apparent_zenith"])
        result.append([az, el, zen])
      return result
    except Exception as e:
      return f"Error: {str(e)}"

Online Calculator

Timestamp or 2D range of timestamps in ISO8601 format.
Latitude north of equator (deg).
Longitude east of prime meridian (deg).
Site elevation above sea level (m).
Atmospheric pressure (Pa).
Solar position algorithm method.
Ambient temperature used in refraction calculation (deg C).