Dear Hannes,
If I understand correctly, you are starting with a "sample weather file" for a location in the northern hemisphere, and modifying the file by changing only the latitude value in the file header. That will cause simulations to fail because SAM uses the latitude, longitude, and time stamp values to calculate hourly solar position angles, which will not be consistent with the solar radiation data for the original northern hemisphere location. For example, the solar radiation data on the summer solstice (June 21) will be for the longest day of the year instead of the shortest day of the year as it would be in the southern hemisphere.
You would be better off using a weather file for a southern hemisphere location. For example, there is a file for Alice Springs (Australia) among the files included with SAM. You can download weather files for other locations from one of the sites listed in
SAM's Help system
.
Best regards,
Paul.