Various mixtures and solutions can be used to repel pigeons, some of which may work better for the specific location than others. Sprinkling or spraying these mixtures on the area where the pigeons roost will successfully repel them, but may cause a bit of a mess at the same time.
Mothballs
Spreading mothballs on your balcony or the place where the pigeons are congregating will quickly make them leave the area. They hate the smell. Mothballs, however, are poisonous to other animals, so make sure any cats or dogs are not able to get to them and eat them. Cayenne pepper also has been found to sometimes be an effective olfactory repellent for pigeons, but mothballs seem to universally be the most effective.
WD-40
WD-40, or other similar lubricant, is useful at repelling pigeons not only because they don't like the WD-40 smell but also because they don't like the slickness under their feet when they attempt to roost on it. WD-40 should be applied daily to keep the application thick and uncomfortable for roosting pigeons. You will be using a large amount of WD-40 by doing this, which could become rather expensive. WD-40 also may corrode the surface of whatever you are spraying it on, so test a small area to make sure the paint or surface you are spraying it on won't be affected.