NAME

       r.sunhours  - Calculates solar elevation, solar azimuth, and sun hours.
       Solar  elevation:  the  angle  between  the direction of the geometric center of the sun’s
       apparent disk and the (idealized) horizon. Solar azimuth: the  angle  from  due  north  in
       clockwise direction.

KEYWORDS

       raster, solar, sun energy, sun position

SYNOPSIS

       r.sunhours
       r.sunhours --help
       r.sunhours   [-ts]    [elevation=name]     [azimuth=name]    [sunhour=name]   year=integer
       [month=integer]    day=integer    [hour=integer]     [minute=integer]     [second=integer]
       [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:
       -t
           Time is local sidereal time, not Greenwich standard time

       -s
           Do not use SOLPOS algorithm of NREL

       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       elevation=name
           Output raster map with solar elevation angle
           Name for output raster map

       azimuth=name
           Output raster map with solar azimuth angle
           Name for output raster map

       sunhour=name
           Output raster map with sunshine hours
           Sunshine hours require SOLPOS use and Greenwich standard time

       year=integer [required]
           Year
           Options: 1950-2050

       month=integer
           Month
           If not given, day is interpreted as day of the year
           Options: 1-12

       day=integer [required]
           Day
           Options: 1-366

       hour=integer
           Hour
           Options: 0-24
           Default: 12

       minute=integer
           Minutes
           Options: 0-60
           Default: 0

       second=integer
           Seconds
           Options: 0-60
           Default: 0

DESCRIPTION

       r.sunhours  calculates  sun elevation and sun azimuth angles for the given time of day and
       each grid cell in the current region.  Additionally, the photoperiod  (sunshine  hours  on
       flat terrain) can be calculated.

       Sun  elevation,  height,  height  angle,  or  solar altitude angle is the angle in degrees
       between the horizon and a line that points from the site towards the centre of the sun.

       The sun azimuth angle is here defined as the azimuth angle in degrees of the sun from  due
       north in a clockwise direction.

       The  time  used  here  is defined such that 12:00 (high noon) is the time when the sun has
       reached its highest point in the sky at the current site, unless the -t flag  is  used  in
       which case time is interpreted as Greenwich standard time.

       If  a  sunhour output map is specified, the module calculates sunshine hours for the given
       day. This option requires both  Greenwhich  standard  time  and  the  use  of  the  SOLPOS
       algorithm by NREL.

NOTES

       To consider also cast shadow effects of the terrain, r.sun has to be used.

EXAMPLES

   Calculating a sun elevation angle map
       Calculate the sun elevation angle map for 2010-10-11 at 14:00h solar time:
       # set computational region to North Carolina state extent
       g.region n=318500 s=-16000 w=124000 e=963000 res=500 -p
       r.sunhours elevation=sun_elev year=2010 month=10 day=11 hour=14 minute=00
       # visualize
       d.mon wx0
       d.rast sun_elev
       d.vect nc_state type=boundary
       d.legend sun_elev -s

       Sun angle map (in degree) of North Carolina for the 2010-10-11 at 14:00h solar time

   Calculate map of photoperiod (insolation time)
       Calculate   photoperiod  of  day-of-year  001  (1st  January)  of  2012  for  the  current
       computational region, ignoring cast shadow effects of the terrain:
       g.region -p
       r.sunhours sunhour=photoperiod_doy_001 year=2012 day=1

Acknowledgements

       Acknowledgements: National Renewable Energy Laboratory for their SOLPOS 2.0  sun  position
       algorithm.

SEE ALSO

        g.region, r.sun, r.sunmask

AUTHOR

       Markus Metz

SOURCE CODE

       Available at: r.sunhours source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual