r.sun(1grass) on Linux
The text c5d15847caab, as Debian 13 (Trixie) shipped it. The page shows this text now.
Solar irradiance and irradiation model. Computes direct (beam), diffuse and reflected solar irradiation raster maps for given day, latitude, surface and atmospheric conditions. Solar parameters (e.g. sunrise, sunset times, declination, extraterrestrial irradiance, daylight length) are saved in the map history file. Alternatively, a local time can be specified to compute solar incidence angle and/or irradiance raster maps. The shadowing effect of the topography is optionally incorporated.