Please find here the link to the Solar Geometry libraries developed by the Mines ParisTech research center:
Solar geometry 1: For the compilation, refer to the files README and INSTALL. There is no example of use of the library, but the codes provide a satisfying number of comments to help using this library.
Solar geometry 2:
Article: Blanc P. and L. Wald, 2012. "The SG2 algorithm for a fast and accurate computation of the position of the sun for multi-decadal time period", Solar Energy 88, 10 (2012). pp 3072-3083
Solar-Geometry-2 in C: This zip compressed file contains the library, a makefile for the Unix environment and an example of use of the library. This is still a code for research, so it contains quite a limited number of comments. As well, no recommendation is given to create the makefile in the Windows environment.