Generally speaking, windows facing south can get enough sunshine and warmth, which is beneficial to indoor environment and health. However, if the environment in the alley is noisy or there are many passing cars, then the windows facing south may make the indoor noise louder and affect the comfort of living.
In addition, if the alley is narrow, the windows facing south may expose the room to the sight of the street and affect privacy. So if you think these problems have an impact on you, you can consider taking some measures to improve it, such as installing curtains or soundproof windows.
In a word, the influence of the window facing south on an alley has advantages and disadvantages, which need to be considered according to the actual situation.