States that testing air and liquid-filled solar collectors according to ANSI/ASHRAE 93-1986 (ASHRAE 1986) has proved difficult in much of the world due to the strict steady-state requirements set forth in the standard. Presents a method of quantifying the level of quasi-steady state using the first-order time response of the collector to weigh changes in energy collected and inlet temperature. Using existing test data from 16 clear days, the method produced thermal performance data that were statistically indeterminate from curves produced using a modified version of the standard. Relaxing the wind and solar radiation restrictions was necessary to obtain a Standard plot. States the method should significantly reduce the time and costs of conducting steady-state thermal performance tests for both air and liquid-based solar collectors.

KEYWORDS: Solar collectors, standards, USA, steady state, performance, testing, flat plate solar collectors.