Hi Leo, > Does anyone know, which is the easiest way to create a *.tm2 or > *.tmy file out of a *.dat?? That depends on what's in a .dat file :-). What is it? There is documentation for the TMY2 file format here: http://rredc.nrel.gov/solar/pubs/tmy2/tmy2_index.html Cheers, Ben