code: def equation_of_time_pvcdrom(dayofyear):
      
      # day angle relative to Vernal Equinox, typically March 22 (day number 81)
      bday = \
          _calculate_simple_day_angle(dayofyear) - (2.0 * np.pi / 365.0) * 80.0
      # same value but about 2x faster than Spencer (1971)
      return 9.87 * np.sin(2.0 * bday) - 7.53 * np.cos(bday) - 1.5 * np.sin(bday)
docs: Equation of time from PVCDROM.
  
      `PVCDROM`_ is a website by Solar Power Lab at Arizona State
      University (ASU)
  
      .. _PVCDROM: http://www.pveducation.org/pvcdrom/2-properties-sunlight/solar-time
  
      Parameters
      ----------
      dayofyear : numeric
  
      Returns
      -------
      equation_of_time : numeric
          Difference in time between solar time and mean solar time in minutes.
  
      References
      ----------
      [1] Soteris A. Kalogirou, "Solar Energy Engineering Processes and
      Systems, 2nd Edition" Elselvier/Academic Press (2009).
  
      See Also
      --------
      equation_of_time_Spencer71