The development and exploitation of wind energy is crucially dependent on short term prognoses for power from wind. Intense efforts have been applied to development and implementation of such prognoses. Traditionally the criterion for a good prognosis is that the prognosis error in terms of the sum of squares of the errors is small. The key point in the paper is the demonstration that a variety of criteria exists. Which one is relevant can not be determined generally but will depend on the circumstances of the organization owning the wind mills and applying the prognosis, as well as the general condition of the electricity system in question. For instance a company responsible for the power balance in a system (could be a system operator) [...]
