Abstract: The present invention concerns a method of producing a data base which includes a plurality of correlation laws, in particular correlation factors, for determining lost energy, which during a stoppage or throttling of a first wind power installation cannot be converted thereby into electrical energy, from the recorded power of at least one reference wind power installation operated in throttled or unthrottled mode, comprising the steps of simultaneously detecting instantaneous power of the first wind power installation and at least one reference wind power installation in the throttled or unthrottled mode, determining a respective correlation law, in particular correlation factor, describing a relationship between the power of the first wind power installation and the power of the at least one reference wind power installation, and storing the at least one correlation law or correlation factor in dependence on at least one boundary condition.