Generated power sudden drop behavior

Dear all,
I simulated a parabolic trough system of 10 MW. Then a parametric simulation was carried out for TES hours and system output. Little later sunset, a sudden drop of generated power can be identified. It drops down up to around 8500 kW. then the generated power shows a constant value at 8500 kW for some time period depending on the TES hrs. I can't understand this behavior, specially the sudden drop.
As well as there is another unpredictable behavior as attached figure.
Also I found that the generated power goes upto -15000kW some times. It can't be Parasitic energy. because parasitic loads are around -2000kW. Can any one explain Why?
I did another simulation with some tilt angles (7 degree,15 degree). My Idea was that when the tilt angle equals to latitude angle, power generation gets maximum. but according to the result, when tilt angle increases, power generation decreases. can any one tell, why the reason is?
the SAM file (I'm talking about the case "PT-SWERA (W/TES-4hrs"), excel file which was used in "excel exchange" command, the results (excel and pdf file) are attached herewith.

Thank you,

I still couldn't find good answer for these. Please help me.

Hello,

For the scenarios with large thermal energy storage capacities, both the daily drop of the power generated by the system, and the large negative values for days of low sunshine appear to be caused by the TES freeze protection requirement, which is determined by the temperature set points on the Thermal Energy Storage input page. You may want to consider increasing the solar field size or adjusting the temperature set points.

As for the tilt angle, the rule of thumb that associates tilt angle = latitude with the maximum annual output does not apply universally to all locations. In your case, it appears that the maximum DNI resource is not in the summer months, so orienting the array toward the summer solstice sun position may not result in the maximum annual output.

Best regards,
Paul.