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How do I derive from ICC-SRCC or Solar Keymark test report the "Incidence angle modifier constant" to use as parameter for a collector (for example Type 45)? Usually, the reports provide various values for different angles.
Type45's incidence angle modifier is of the form IAM = 1 - b0 * S, where S = (1/cos(incidence angle)-1)
What I would recommend is that you take the IAM data from ICC-SRCC or Keymark, plot and curve fit it to the form of Type45's IAM algorithm. You should then be able to get the required value of b0.
~david
Thank @DavidBradley you for your feedback. I did it indeed and found that, there are usually two distinct slopes (see enclosed file), for all c collectors I have checked. I wondered if I have to select one of them or it is still make sense to keep an average slope.
If I am reading the plot correctly the linear curve fit if IAM vs S is going to underpredict the IAM at near-normal incidence angles (meaning you'll collect a little bit less energy) and overpredict (very slightly) the IAM at higher incidence angles (when there isn't as much energy incident on the collector).
I am not entirely clear about which "slopes" you are referring to in your reply. Do you mean that the IAM vs incidence angle plot could be approximated by two lines each having a its own slope?
~david
