Hi Matthew,
The technical manual does seem imply that "field thermal power incident" includes the mirror derates. However, after looking at the code, we note that the SAM output "field thermal power incident" is the incident power on the mirrors before any optical losses.
Regarding IAM vs cosine effects, the IAM accounts for all solar positioning losses that aren't explicitly modeled, such as the cosine effect and row losses. That is why field thermal power incident and field thermal power incident after cosine have different values.
Finally, the ratio of receiver thermal power incident to field thermal power incident is dependent on multiple optical derates. For the collectors these are: incidence angle modifiers, tracking error, general optical error, geometry effects, mirror reflectance, and dirt on mirror. Row shadowing and end losses also affect the collector performance.
For this case, the receiver envelope is not considered because the glass is broken. Therefore, the remaining optical derates for the receiver are bellows shadowing and dirt on receiver. Currently, the incident power on the receiver does not include the power reflected away from the receiver via it's absorptance term, but we have created an issue to include this power in future versions:
github.com/NREL/SAM/issues/1441
.
Best regards,
Paul.