August 5 2015

Why windpower is predictable 

One of the loudest criticisms of wind power is that it is unpredictable and by extension somehow unsuited to the power system. It is also noted that large thermal generators can take several hours to be brought online so predictability is important. But is wind power unpredictable?

One answer comes from the work of Isaac Van der Hoven who was a meteorologist at the air resources laboratory of the National Oceanographic and Atmospheric Administration. This chart which Van der Hoven published* in the Journal of Meteorology in 1957 demonstrates the variability of wind over different timescales. 

Note the peak at the 2 minute level – this is due to gusting

Note also a diurnal peak (day/night variations) and the largest peak at a period of around 4 days. This peak reflects the average time for a storm system to pass across the measuring point.

The variability at the half hour, 1 hour level is low. This shows that the wind level doesn’t experience large changes from hour to hour.

It is also possible to infer from this graph that accurate forecasting of instantaneous wind speed is difficult, that forecasting average wind speed a few hours ahead is more realistic, and that forecasts for several days out will be dependent on the accuracy with which you can forecast the movement of weather systems.

Since it is the hour to hour forecasting that is most important for electricity systems with thermal generation, wind power is - in fact – well suited as a generation source.

 *Isaac Van der Hoven, “Power Spectrum of Horizontal Wind Speed in the Frequency Range from 0.0007 to 900 Cycles per Hour”, Journal of Meteorology, Vol 14 (1957), pp 160-164