Dear Will,
Yes, you can do that.
For the Detailed PV model, you can just check the
Tilt=latitude check box on the System Design page.
For PVWatts, you have to be a little careful because before you run a simulation, the
might store the value that you see on the Location and Resource page, not the value from the weather file. To make sure you are getting the value from the weather file and not from the user interface, you should run a simulation before reading the tilt value like this, assuming you set the weather file before this code snippet:
output('Latitude before simulation: ' + lat);
simulate();
output('Latitude after simulation: ' + lat);
latitude = get('lat');
set('tilt',latitude);
outln('tilt = ' + tilt);
outln('latitude = ' + lat);
simulate();
Best regards,
Paul.