How much energy does a wind turbine store?

First, the turbine itself does not store the energy. One needs a battery or capacitor for that. The amount of energy a turbine produces is determined by the size of the turbine and the speed of the blades, and the average RPMs in a given day. Short answer: it depends. It is best to couple the turbine as a backup for a solar array for times when the sun is not sufficient to power the cells, on the theory that when the sun is not shining during the day, the wind might be blowing because of a storm. [The British put low power turbines next to railroad tracks to power the crossing signals. The wind of the passing trains powers the them.]