Parabolic Trough - Physical - IAM formula

Hello, I am running some simulations with the Parabolic Trough model and I would like to know:

(1) the formula for the IAM in the Parabolic Trough (Physical) model and
(2) how the efficiency of the collector is calculated (loss method?)

Doc Page: nrel-pysam.readthedocs.io/en/latest/modules/TroughPhysical.html

Variable: IAM_matrix
Description: IAM coefficients, matrix for 4 collectors
Default Values SAM GUI: 1, 0.0327, -0.1351

Many thanks! 

Hi Paolo,

The IAM_matrix variable is equivalent to the "Incidence angle modifier coefficients" input on the Collectors (SCA) page in SAM. This is an input. You can see how the model calculates the incidence angle modifier (IAM) from the coefficients in the source code on GitHub:

github.com/NREL/ssc/blob/990f351727867f7d71dcec1705cfa74dca8750b9/ssc/cmod_csp_common_eqns.cpp#L1044

The collector optical efficiency calculations are here:

github.com/NREL/ssc/blob/990f351727867f7d71dcec1705cfa74dca8750b9/tcs/csp_solver_trough_collector_receiver.cpp#L4357

Best regards,
Paul.