The 2001/77/CE European Commission Directive sets the target of 22% and 39% of gross electricity generation from renewables for the Europe and Portugal by 2010. To satisfy this target, it is planned the installation of additional generation capacity from renewable sources (5077 MW) in which the biggest part of the increase it is in wind power, with an installed power in 2010 of 3750 MW. If the contribution of this production vector in energy terms is not a cause of concern, the power balance, and therefore the impact in the supply security needs attention due to the intermittent and random character of this production option. The connection of wind turbines to an electricity grid can potentially affect supply reliability and power quality, due to the unpredictable fluctuations in wind power output. In a scenario of large scale penetration of renewable production from wind and other intermittent resources, it is fundamental that the Portuguese electric system have appropriate means to compensate the effects of the variability and randomness of the wind power availability.