In order to determine the efficiency parameters of solar thermal collectors according to ISO 9806 or EN 12975, two different procedures can be used: the steady state test method and the quasi dy­namic test method.

During the steady state test, all boundary conditions such as solar radiance, ambient temperature and collector inlet temperature must be constant. After recording data points over a representative range of operating conditions, the collector efficiency curve can be determined by means of multi­linear regression using the least square method.

During the quasi dynamic test the boundary conditions must vary. Based on a series of measure­ments, specific collector parameters are determined, as well. With the quasi dynamic test method, additional parameters such as the heat capacity of the collector and the incident angle modifier co­efficient can be determined in addition to the efficiency curve.