Usage

This package provides a set of functions for calculating solar geometry parameters. Below is a summary of each function and its usage:

The sun-angles Python package calculates solar zenith and azimuth and daylight hours.

Gregory H. Halverson (they/them)
[email protected]
NASA Jet Propulsion Laboratory 329G

Installation

This package is availabe on PyPi as a pip package as sun-angles with a dash.

pip install sun-angles

Usage

Import this package as sun_angles with an under-score.

import sun_angles

1. day_angle_rad_from_DOY(DOY)

• Description: Calculates the day angle (in radians) from the day of the year.
• Parameters: DOY (int, numpy array, or Raster): Day of year (1–365).
• Returns: Day angle in radians.
• Reference: Duffie, J. A., & Beckman, W. A. (2013). Solar Engineering of Thermal Processes (4th ed.). Wiley.

2. solar_dec_deg_from_day_angle_rad(day_angle_rad)

• Description: Computes the solar declination (in degrees) from the day angle (in radians).
• Parameters: day_angle_rad (float, numpy array, or Raster): Day angle in radians.
• Returns: Solar declination in degrees.
• Reference: Duffie, J. A., & Beckman, W. A. (2013). Solar Engineering of Thermal Processes (4th ed.). Wiley.

3. SHA_deg_from_DOY_lat(DOY, latitude)

• Description: Calculates the sunrise hour angle (SHA, in degrees) from day of year and latitude.
• Parameters:
  • DOY (int, numpy array, or Raster): Day of year.
  • latitude (float, numpy array, or Raster): Latitude in degrees.
• Returns: Sunrise hour angle in degrees.
• Reference: Duffie, J. A., & Beckman, W. A. (2013). Solar Engineering of Thermal Processes (4th ed.). Wiley.

4. daylight_from_SHA(SHA_deg)

• Description: Converts sunrise hour angle (SHA, in degrees) to daylight hours.
• Parameters: SHA_deg (float, numpy array, or Raster): Sunrise hour angle in degrees.
• Returns: Daylight hours.
• References:
  • Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop evapotranspiration-Guidelines for computing crop water requirements-FAO Irrigation and drainage paper 56. FAO, Rome, 300(9).
  • Duffie, J. A., & Beckman, W. A. (2013). Solar Engineering of Thermal Processes (4th ed.). Wiley.

5. calculate_daylight(DOY=None, lat=None, SHA_deg=None, datetime_UTC=None, geometry=None)

• Description: Calculates daylight hours for a given day and location. Flexible input: provide SHA directly, or let the function compute it from DOY and latitude.
• Parameters:
  • DOY (optional): Day of year.
  • lat (optional): Latitude in degrees.
  • SHA_deg (optional): Sunrise hour angle in degrees.
  • datetime_UTC (optional): Datetime in UTC.
  • geometry (optional): Geometry object with latitude.
• Returns: Daylight hours.

6. sunrise_from_SHA(SHA_deg)

• Description: Calculates the sunrise hour from the sunrise hour angle (SHA, in degrees).
• Parameters: SHA_deg (float, numpy array, or Raster): Sunrise hour angle in degrees.
• Returns: Sunrise hour.
• Reference: Duffie, J.A., & Beckman, W.A. (2013). Solar Engineering of Thermal Processes. John Wiley & Sons.

7. SZA_deg_from_lat_dec_hour(latitude, solar_dec_deg, hour)

• Description: Calculates the solar zenith angle (SZA, in degrees) from latitude, solar declination, and hour.
• Parameters:
  • latitude (float, numpy array, or Raster): Latitude in degrees.
  • solar_dec_deg (float, numpy array, or Raster): Solar declination in degrees.
  • hour (float, numpy array, or Raster): Solar time in hours.
• Returns: Solar zenith angle in degrees.
• Reference: Muneer, T., & Fairooz, F. (2005). Solar radiation model. Applied energy, 81(4), 419-437.

8. calculate_SZA_from_DOY_and_hour(lat, lon, DOY, hour)

• Description: Calculates the solar zenith angle (SZA, in degrees) from latitude, longitude, day of year, and hour.
• Parameters:
  • lat (float or array): Latitude in degrees.
  • lon (float or array): Longitude in degrees.
  • DOY (int or array): Day of year.
  • hour (float or array): Hour of day.
• Returns: Solar zenith angle in degrees.

9. calculate_SZA_from_datetime(time_UTC, lat, lon)

• Description: Calculates the solar zenith angle (SZA, in degrees) for a given UTC time, latitude, and longitude.
• Parameters:
  • time_UTC (datetime): UTC time.
  • lat (float): Latitude in degrees.
  • lon (float): Longitude in degrees.
• Returns: Solar zenith angle in degrees.

10. calculate_solar_azimuth(solar_dec_deg, SZA_deg, hour)

• Description: Calculates the solar azimuth angle (in degrees) from solar declination, solar zenith angle, and hour.
• Parameters:
  • solar_dec_deg (float, numpy array, or Raster): Solar declination in degrees.
  • SZA_deg (float, numpy array, or Raster): Solar zenith angle in degrees.
  • hour (float, numpy array, or Raster): Hour of the day.
• Reference: Muneer, T., & Fairooz, F. (2005). Solar radiation and daylight models: for the energy efficient design of buildings. Architectural Press.

References

• Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop evapotranspiration-Guidelines for computing crop water requirements-FAO Irrigation and drainage paper 56. FAO, Rome, 300(9).
• Duffie, J. A., & Beckman, W. A. (2013). Solar Engineering of Thermal Processes (4th ed.). Wiley.
• Muneer, T., & Fairooz, F. (2005). Solar radiation model. Applied energy, 81(4), 419-437.
• Muneer, T., & Fairooz, F. (2005). Solar radiation and daylight models: for the energy efficient design of buildings. Architectural Press.