Incidence angle modifier

Hi Support People,

While calculating the Incidence angle modifier I'm used to having a matrix of values for longitudinal and transversal IAM for various incidence angle combinations for tubular collectors.

for eg

Dir. | 0° | 15° | 30° | 45° | 60° | 75° | 90° |

---

Trans. IAM | 1.00 | 1.01 | 1.03 | 1.05 | 1.04 | 1.02 | 0.00 |
Long. IAM | 1.00 | 1.00 | 0.98 | 0.96 | 0.90 | 0.71 | 0.00 |


Can you tell me how the SAM suggests single value of IAM while choosing the collectors for Solar hot water System?

Regards
Mavadi

Dear Mavadi,

SAM's Solar Water Heating model uses the incidence angle modifier equations from Duffie and Beckman's Solar Engineering of Thermal Processes for flat collectors, which use a single incidence angle modifier coefficient. These equations are described in Section 6.17 of the Fourth Edition of the book. You can see how these equations are implemented in SAM in the following source code around Line 435:

github.com/NREL/ssc/blob/develop/ssc/cmod_swh.cpp

Best regards,
Paul.