# Trough model: incidence angle at design conditions

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tahir.gafurov
Trough model: incidence angle at design conditions

Dear Paul,

I have a very simple question regarding the solar field sizing in Parabolic Trough Model. What is the value of the solar incidence angle at design/reference conditions? Is it zero or is it calculated assuming solar noon at summer solstice like in Power Tower Model? Unfortunately the available documentation doesn't specify it.

Thank you for your time and help. And Happy Easter!

Best Regards,

Tahir

Paul Gilman

Dear Tahir,

Best regards,
Paul.

tahir.gafurov

Dear Paul,

I am afraid I am still confused. In your previous reply in the provided link you wrote:
/start of quote
The physical trough model uses solar noon on the summer solstice to calculate the Incidence Angle Modifier (IAM) and End Loss at Design values on the Collectors page.
"Design Conditions" for the Optical Efficiency at Design value means that the sun is directly above the receiver. The Optical Efficiency at Design value therefore does not include IAM and end losses.
/end of quote
This seems contradictory to me. At solar noon on the summer solstice the incidence angle for trough collectors in general will NOT be zero, which means that IAM and End losses should be included. Considering this could you please confirm/clarify once again the following aspects regarding the solar field sizing for trough model:
1. Is the incidence angle calculated assuming solar noon at summer solstice?
2. Are IAM and End losses ignored, even though the incidence angle is NOT zero?

Thank you very much for your help and time.

Best Regards,
Tahir

Paul Gilman

Dear Tahir,

1. Yes, SAM calculates the incidence angle assuming solar noon at summer solstice.

2. Yes, the SAM ignores the IAM and end losses for the design-point calculations. The optical efficiency at design value represents collector geometry and other location-independent optical parameters (shown on the Collectors page). This modeling approach isolates the optical parameters that depend on collector design from those determined by location. Another approach that includes the IAM and end losses in the design value as you suggest would also be an acceptable modeling approach, but is not the one we chose for SAM.

Best regards,
Paul.

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