<Then all you need to do is convert the tmy3 to tmy2 for trnsys:> Or if you have a Fortran compiler, you could ask the TESS guys for the latest version of Type 15 which reads TMY-3 files.... Jeff Jeff Thornton President - TESS, LLC 2916 Marketplace Drive - Suite 104 Madison WI 53719 USA Phone: 608-274-2577 Fax: 608-278-1475 E-mail: thornton@tess-inc.com Web: www.tess-inc.com