The main concern of system operators is the changes from hour to hour. An analysis based on 30 MW steps shows that for over 30% of the time the power changes within an hour were less than 30 MW (figure). Such small fluctuations are of no concern as the system operator needs to guard against a far greater potential threat to the grid -- the loss of the largest power station on the system, at 760 MW.
Furthermore, the data reveal that power changes of 60 MW within an hour were recorded for 10% of the time, but power changes over 200 MW (up or down) were recorded for less than 0.4% of the time. The maximum recorded changes within an hour were 317 MW upward and 270 MW downward, so the maximum change corresponds to a little under 20% of the installed wind capacity. Interestingly, the maximum increase was greater than the maximum decrease, which seems to put paid to the idea that large power excursions occur in high winds when a number of machines reach their cut-out wind speed.
The pattern of wind fluctuations from a large amount of wind energy gives the system operator in western Denmark the essential information needed to keep supply stable. It shows that the maximum power excursion is less than the change in generation which will occur if the output from the largest power station (760 MW) on the system were lost.
The pattern of wind fluctuations is almost identical to those measured by Germany's institute for solar energy research, ISET. It is in charge of monitoring 350 MW of wind power. Again, the largest-ever fluctuation within an hour was 20% of the installed capacity.