Tracking the sun with mobile app
There is an Android app called dioptra that is able to use sensors in your phone to produce pictures with information about azimuth and elevation of the object in the center of the frame.
In theory it can be used to track the sun directly in a much simpler way than measuring shadows. Just point and shoot at the sun.
Of course, our spreadsheet needs to be adjusted for predicting sun angles instead of shadows. But this is simple enough.