There are four parameters you must set to display shadows that accurately portray the real world:
• Geographic Orientation — Relationship of True North to the model.
• Geographic Location — Latitude and Longitude
• Time — Year, Month, Day, Hour and Minute
• UTC Offset — The difference between local time and the Coordinated Universal Time standard.
By default, the solid green Y Axis is true north in SketchUp.
The same is true if you geo-locate the model via Model Info > Geo-location > Set Manual Location
However, the Y Axis is no longer true north if you geo-locate the model via SketchUp's Add Location.
The simplest and most direct approach to shadow analysis is to build the model along the Default Axes.
Then, geo-locate the model via Model Info > Geo-location > Set Manual Location
Install the Solar North plugin (SketchUp Pro only) and use it to set true north in relation to the model.
You can verify your model with data from the United States Naval Observatory:
Complete Sun and Moon Data for One Day: Locations Worldwide
Sun or Moon Altitude/Azimuth Table: Locations Worldwide