I have gone through the article of NREL manual for parabolic trough CSP and also receiver analysis article. But none of those article is clear about how to find HTF bulk temperature (T1) for EES model. How do I find T1 or guess the value for iteration. T1 is the mean bulk HTF temperature for the receiver.
The physical trough model reports hourly HTF temperatures a the field outlet and inlet and at the power cycle inlet and outlet. You should be able to use that data to calculate the value you need for your model.