Storm Barney - Too Strong for Wind Turbines

Storm Barney hit Ireland's shores last week bringing strong winds, the fuel for our wind farm fleet. But a noticeable thing happened. Between 1pm and 6pm, wind energy output dropped by as much as 44% :

Let's have a look at wind speeds during the day. As you can see below, the highest wind speeds occurred during 12 and 6pm, the period when wind energy output began declining. Wind speeds reached between 30 and 50 knots, or 15 and 25 metres per second. Air pressure went as low as 980 hpa. Not as low as The Night of the Big Wind in 1839 where it went down to 920hpa or the hurricane in 1988 where it went down to 950hpa.

Dublin Airport

Cork Airport

Mullingar

Valentia

Mace Head

The diagram below shows the cut in and cut out speed of a wind turbine in metres per second :

All stations in Ireland record wind speeds at 10m above ground level. Wind turbines are 8-15 
times higher than this. So at station level, we are still within the cut out speed, but higher up
at hub height, the wind speeds are stronger and most likely outside cut out speed. 

So this might explain why during the highest winds of the storm, wind turbines were being shutdown. 

Which means we need back up dispatchable power stations during storms aswell as calm 
spells.