Physical Parabolic Trough Model: HCE support bracket

Dear Paul,
i am working with your physical parabolic trough Model, with SAM 2013.9.20. I realize that in the function of the HCE Support bracket there is a mistake in Terms of the Units.
During the calculation of a case with WIND (V_6 > 0.1), you have forgotten to delete the change of Units from the Forristall model in EES. Therefore, the thermal difussivities (Alpha_brac, Alpha_6) are underestimated.
Best regards,

Juan Haces

Dear Juan,

Thank you for pointing out this error with the physical trough model. According to our tests, it causes a small underestimate of the total annual energy of about 0.1%. We will fix it in the next version of SAM.

Best regards,
Paul.

Dear Paul,

I have also seen a strange result. It is going about the 'collector cosine effect - cos Theta hourly'.

For a long time, i have seen the curves related to the cosine effect as a sinus function. In the results of SAM, at the beginning and ending of the day, we can see that the result do not follow a sinus equation. It does not match with the equations of the cosine effect. I am trying to find an argument in the code of the type250, but unfortunately, am not finding out it. Could you help me?

Thanks in advance!

Best regards,
Juan Haces

Dear Juan,

I'm not sure what you mean. Can you clarify your question?

Best regards,
Paul.

Dear Paul,

sorry for the delay. I meant that, if someone looks into the data of the hourly data, related to the collector cossine effect, the results are weird.

DNI (W/m2) hourly Collector cosine effect - cos theta hourly
0 0
0 0
0 0
0 0
0 0
0 0
0 0
232 0
750 0.622684
908 0.732077
976 0.652716
1006 0.593174
1014 0.571773
1003 0.596744
966 0.658923
893 0.739501
717 0.536337
178 0
0 0
0 0
0 0


As you can see here, at the beginning (750 - 0.6222684) and at the ending (717 - 0.536337) the cosine goes down. It seems strange. I'll be pleased, if you can clarify me that.

Best regards,
Juan Haces

Hello Juan,

By convention, weather file data is recorded according to local time such that weather readings are recorded on the hour (for hourly files) or averaged over the hour to coincide with actual clock time. Clock time is almost always different from solar time because any given location is not (usually) exactly along the standard meridian. SAM's simulation engine runs off of local weather file time, and calculates sun position according to the midpoint of the each hour. Often, this leads to asymmetries in things like cosine loss, peak sun position, morning/afternoon production, etc.

Regards,

Mike Wagner
NREL