Among the limiting factors to the penetration of wind and solar energy is the variable nature and limit to predictability of wind speed and solar irradiance .To maintain grid stability, it is fundamental to know a priori the renewable energy production that can be combined with other less variable and more predictable sources to satisfy the energy demand 1. In a deregulated market, it is crucial for the utility companies that provide electricity to be able to deliver the committed energy to the grid. In this sense this is a challenge for wind and solar energy when compared to other types of energy sources because of their intrinsic limited predictability . Accurate wind and solar power predictions and reliable estimates of their uncertainty are key aspects to mitigate these disadvantages.