SolTrack

A simple, free, fast and accurate routine to compute the position of the Sun

SolTrack is a simple, free, fast and accurate routine to compute the position of the Sun. The code can be used to track the Sun on low-spec machine, such as a microcontroller or PLC, and can be used for e.g. (highly) concentrated (photovoltaic) solar power.
SolTrack has been developed by Marc van der Sluys, Paul van Kan and Jurgen Reintjes, of the Lectorate of Sustainable Energy at the HAN University of applied sciences in Arnhem, the Netherlands. The code is derived from the astronomical Fortran library libTheSky and is available under the terms of the GNU LGPL v.3.
Reference:
http://soltrack.sourceforge.net/