CSP-Parabolic Trough - Optimal tilt angle

Some r eferences have reported optimal tilt angle for parabolic trough to be zero, while other, including, CSP Best Practices Study (2020) , Section 5.3, recommend it to to be equal to the latitude of the site. Can somebody please explain it for me.
Regards.

Hi Muhammad,

I could not find mention of setting the tilt angle to the site latitude in the CSP best practices study.

Page 135 does have this statement, which describes adjusting the azimuth angle to increase annual generation, but does not mention the tilt angle or latitude:

Calculations with real measured DNI at a location in Abu Dhabi showed that an increase in annual electricity generation of 2.8% would be possible by rotating the solar collector axis 68° counterclockwise from the north/south orientation.

Best regards,
Paul.

Hi Paul
Thank you for prompt response.
Abu Dhabi latitude is 22. The number '68' came from 90-22=68 in my understanding.

I am trying to simulate parabolic trough based 50 MW power plant for Pakistan. While in-putting info to SAM, parabolic trough physical/ solar field section, Collector Orientation sub section, it asks for 'Collector Tilt" and 'Azimuth'. I have tried Tilt = 0 and Azimuth= 90-33.5=56.5. (33.5 is the latitude for my location). However, it is giving me following error;

exec fail(trough_physical): At time = 270000, CR_OFF__PC_OFF__TES_OFF__AUX_OFF failed
Simulation trough_physical failed :The calculated field design mass flow rate of 2773.02 kg/s is greater than the maximum defined by the max single loop flow rate and number of loops (2172.00 kg/s). The design mass flow rate is reset to the latter.
gen not assigned
Simulation grid failed :gen not assigned
SSC requires input 'gen', but was not found in the SAM UI or from previous simulations
Simulation utilityrate5 failed :precheck input: variable 'gen' (System power generated) required but not assigned
SSC requires input 'annual_energy_value', but was not found in the SAM UI or from previous simulations
Simulation cashloan failed :precheck input: variable 'annual_energy_value' (Energy value) required but not assigned

Would be grateful if you can explain whats wrong here.
Best Regards.
Muhammad Zeeshan

Dear Muhammad,

I don't think that error message is caused by the tilt and azimuth angle. You can try running the model with the default Tilt=0 and Azimuth=0 to see if you still get the error.

The tilt angle of zero means that the tracking axis is horizontal. For the parabolic trough model, and azimuth angle of zero means that the tracking axis is north-south, or perpendicular to the equator. So Tilt = 0 and Azimuth = 0 means the collectors rotate from East to West throughout the day on a horizontal axis.

Best regards,
Paul.