Finding a good location for your BatBnB requires weighing many factors against each other. Some factors will increase your chances of occupancy more than others, so the key to optimizing your occupancy chances is finding the location with the right combination of these factors.
As far as orientation, this is a less important factor than the duration of direct sunlight. 6+ hours of direct sunlight per day is ideal and will keep your BatBnB’s inhabitants warm and happy.
However, the orientation of South or East both have their benefits:
South-facing will keep your BatBnB warmer for longer as the colder seasons come and go and the sun’s path crosses lower in the sky.
East-facing will allow your BatBnB to be hit with the morning sun and will warm the unit shortly after bats have returned from hunting at night—keeping the BatBnB warmer for longer while they are present
West-facing is less ideal, as it would warm the box during the evening, only keeping it warm for a short while before the bats leave to go hunting).
Furthermore, if you mount your BatBnB on a pole, it may see less effect from orientation. A building completely blocks the back of the unit from receiving sun, while a pole only slightly blocks the sun.
Once again, receiving more direct sunlight would largely override the benefits gained by the orientation.