The wind speed quickly changes by day-night and from day to day. Energetically the most apt wind characteristic is wind power density (WPD). Monthly average WPD depends on month and on location. At sea shore WPD is greatest. Instantaneous WPD changes fast in vast ranges. This imposes the problems of power control for reserve power supply. The mean wind speed is not informative. For energetic characteristic, the cube root mean cube value is more apt. Dislocating the wind generators evenly along cost line, summary WPD will change slowly, fluctuation range can be less wich will require less reserve power.