Joe,
Sorry but I've to argue you there. Having data of -0:30-0:30 convention in Energyplus means that your data is half an hour ahead in time. You have to give that information to EP, this is done by adding 7.5 degrees (going eastwards).
E.g. at time stamp 6:00 EP would normally do sun position calculation using the 5:30 time stamp, because of the TimeHourOffset=-0.5 setting. But with data in -0:30-0:30 format we want it to make the sun position calculation with the 6:00 time stamp instead, right? Adding 7.5 degrees takes out the TimeHourOffset=-0.5 parameter (+7.5 degrees longitudes equals +0.5 hour on the clock => 7.5 degrees + -0.5 hours = 0), thus the sun position calculation is correctly done at the 6:00 time stamp.
I agree it is confusing though.
Regards,
Lukas