A survey on different methods for rating the thermal performance of so
lar collectors in transient conditions has been made. Two inexpensive
methods (Saunier's and Exell's) have been selected for an extensive co
mparative study. The methods are discussed in detail and test sequence
s are explained. The methods are applied to a flat-plate solar collect
or, and their output results are compared with the steady state ASHRAE
standard. It is seen that a very good estimation of collector perform
ance characteristics could be obtained from Saunier's method, but Exel
l's method may not be suitable for testing conventional collectors. Re
sults of not more than 7% deviation from steady state values are obtai
ned from Saunier's test despite some inconveniences in conducting the
tests. (C) 1997 Elsevier Science Ltd.