SAM Getincidentradiation

Dear Paul,

i received a weather file where the data are shifted to GMT 0, even when the GMT is different. In order to ensure that the data are reliable, i did a pre-calculation: I run SAM with the Parabolic Trough Model and the data. As expected, the simulation was stopped due to more than 400 warnings: 'The calculated value of the beam radiation exceeded the maximum possible beam radiation for this timestep. The beam radiation has been set to the extraterrestrial radiation for this timestep.' On the other hand, i run the weather data with other models like PV-Flate and CSP Molten Salt Power Tower. Unfortunately the simulation with the received weather data has run without problems.

Since i knew that the radiation processors are different for each model, i have extracted the SAM Getincidentradiation function from the 'type 15' and 'SAM_GetIncidentRadiation.for' and tested it by myself. I have tested the same weather data, but i have not received the same warnings. The function works fine, without stops.

I would like to ask you about the inputs parameters of the Getincidentradiation function. I am giving the following values:

Date, hour, Latitude, Longitude, Timezone from the weather data

Azimuth: 0°
RAD_IN_MODE: 1 which means reading from GHI and DNI, instead of Diffuse.
Mode_Track: 3 since the troughs are 1-axis and they rotate about a fixed axis.
Mode_Tilt: 4 since the Perez model seems to be the best.

RHOG:1, as i think that there is no ground reflectance for non-snow covered periods.
SLOPE: 0°

Should i consider more parameters for the function? Am i missing anything? Because i find really weird that i am not getting the same results as SAM for this part of the program.

Thank you in advance.

Best regards,
Juan Haces

Dear Juan,

The weather file algorithm for the physical trough model performs some checks on the DNI values for each hour to see if they are reasonable given the solar position for that hour and solar constant. The other models do not perform this check. SAM determines the current hour for a given row in the file based on the assumption that the first row of data in the weather file is for the hour ending at 1 a.m. on January 1. It calculates the solar position based on the current hour, latitude, longitude, and time zone.

Best regards,
Paul.