Dear Sebastian,
Because the abbreviation PT could stand for power tower or parabolic trough, and because SAM has two parabolic trough models, I'm not sure which model you are using. However, I think the answer is basically the same for any of the CSP models.
If you specify too large of a solar field (too high of a solar multiple, or too high of a field aperture area), then the hourly solar field thermal output may exceed the hourly power block thermal input energy. You can look at the hourly dumped energy and the field operation fraction variables for clues that the field is oversized: High dumped thermal energy values indicating that the field is producing more energy than the power block can use, or field operation fractions (fraction of the field that is defocused) of much less than 1 for many sunlight hours indicating that the collectors are frequently defocusing in an effort to reduce the field thermal output.
In other words, the solar field area in your design is probably too high for the combination of solar resource and power block capacity.
Best regards,
Paul.
