This document specifies two procedures to verify the performance of solar thermal collector fields. The collectors in the fields can be glazed flat plate collectors, evacuated tube collectors and/or tracking, concentrating collectors. The check can be done on the thermal power output of the collector field - this is described in the main part of the document. The check also be done on the daily yield of the collector field - this is described in informative annex. The document specifies for the two procedures how to compare a measured output with a calculated one. The document applies for all sizes of collector fields.