Nowadays wind energy comprises an established power generation solution that competes on equal terms with conventional thermal power generation technologies. On the other hand, the inherent characteristic of intermittent energy production, due to the stochastic nature of wind, still comprises the main drawback of wind power. In this regard, one of the most significant factors responsible for the reduction of the wind turbines' energy yield is the machines' technical unavailability. Realizing the important role of technical availability throughout the wind energy technology evolution, an overview of influencing factors and operational experience from wind farms around the globe are currently provided, while accordingly, a proxy prediction model is developed for the estimation of technical availability and the determination of its impact on the annual energy yield of a wind farm. Application results obtained for several case studies indicate the importance of the technical availability factor on the annual energy yield, while finally, the developed model is validated with the use of long-term real operation data from a wind farm installed on the island of Ikaria, Greece.