If you want the low-tech solution, here is a recipe that definitely resolved it for me:

- One big spoon of cinnamon

- One big spoon of chilli peppers

- Half a bottle of cheap, cleaning vinegar

Spray it in all the places that the pigeons want to land. I am doing that once a week and it is enough to keep them away. If you clean your whole balcony with it, you might be able to go through most of the spring - when I think they really get annoying because they are looking for a place to make a nest.