Steady State (SS) versus Quasi-dynamic (QD) test methodology
For determination of thermal performance of solar collectors, measurement of the environmental and of working conditions relevant for the collector behaviour is needed. The test methodologies for this determination, steady state (SS) and quasi-dynamic (QD), considered in EN 12975  have different requirements for test.
Table 1 summarizes the main requirements set out in the standard EN 12975-2 .
The less stringent limits on the validation of test periods for the QD test method mean that this method can be used to gather useful information during almost the whole daylight period throughout the year.
Considering a fix stand for installation of the collector to be tested, to perform a SS test, the period useful for test is reduced to a couple of hours on a day with clear sky conditions. This period of time to test according to SS test method can be larger if a tracking stand is used. But cloudy days can not be used for SS test method, independent of the type of stand used.
For QD test method, a clear day corresponds to almost 8 hours useful for test and cloudy days also give useful information for QD test method.
Table 1: Test conditions and allowable deviations in relation to the mean values for a test period.
Regarding the mean values for a stable test period (Steady-State test) or for the total test period (Quasi-Dynamic test).
If there is no indication to the contrary, fluid flow rate should be approximately 0.2 kg. s-1 per square metre of collector reference area (A). Flow should be kept stable at ± 1% of the value determined during each test period, and should vary by no more than ± 10% compared to the other test periods._________________________________________________