You don't need expensive glass cleaners for streak-free windows. Certain home remedies work just as well.
Shampoo has a similar effect to glass cleaner because it also contains surfactants, glycerin and alcohol. It's best to choose a cloudy day to clean windows, as direct sunlight will cause the windows to dry too quickly and streaks will appear. Simply add a cup of vinegar essence to a bucket of water and clean as usual. Mix a dash of mineral spirits with two liters of cold water and apply the solution. Spirit evaporates quickly and leaves no streaks.