Storm Lorenzo was only a gust compared to Storm Ulysses in 1903

James Joyce's classic novel Ulysses was based in Dublin in the year 1904. In the Aeolus chapter, a severe weather event is mentioned :

Lady Dudley was walking home through the park to see all the trees that were blown down by that cyclone last year.

In Don Gifford's 1974 book, Notes for Joyce, it is explained that this refers to one of the most severe gales in Dublin's history and was compared at the time to that of 1839 (the night of the big wind). The gale caused great damage to property and particularly to trees in Phoenix Park. It is estimated that between 1000-3000 trees were uprooted in the park. In parts of the country it was reported that whole woods were leveled.

A cyclone that could bring down so many trees in Dublin would be seen as a catastrophic event today, and final proof of man made climate change / the end of the world. But we don't get storms that have this much force anymore, they are a thing of the past. Historic climatic events such as in 1839 and 1903 show that the climate, if anything, has actually improved in Ireland.

Storms Linked to Power Station Trips

Eirgrid published this list of power station trips from the past few months:




I couldnt help but notice that most of these dates coincided with storms or very windy conditions:

5th october - Cyclone Xavier
12th october - Hurricane Ophelia
16th october - Hurricane Ophelia
21st october - Storm Brian
27th November - gale force winds
24th December - record wind penetration on the grid
3rd January - Storm Eleanor
17th January - Storm Fionn

It appears that as very high amounts of wind generation is allowed into the grid, the frequency can drop to a dangerously low level.

One of our key tasks is to maintain balance between electricity supply and electricity demand. Electrical frequency is the measure of balance between supply and demand. When supply and demand are balanced, the electrical frequency is at 50 Hz. We must maintain this balance on the system all day, every day. The normal operational frequency range is 49.8 Hz to 50.2 Hz [Eirgrid].

You can see from the above diagram that the frequency has dropped below 49.8Hz on a few occasions over this period.  As a result, the power station tripped and went offline. This then results in the frequency falling even further. At this stage, cutting demand is one of the few options open to the grid operator. This may explain some of the blackouts on these days.

Storm Desmond - the problem with too much wind energy in one graph

Forecasted Wind energy output for 6th December, the day after Storm Desmond, shows a loss in wind generation of 91%

As I write, Storm Desmond is raging outside my window and wind energy output is providing almost 50% of demand. It is coming at a price, however, with ESB Networks reporting that about 12,000 customers had to go without power today due to damaged cables. But electricity is not just required on a Saturday, it is required every day. According to Eirgrid forecasters, wind energy output is forecast to drop by as much as 91% tomorrow, from nearly 2,000MW to 160MW over 16 hours. (a drop in capacity factor from 87% to just 7%)

This explains why wind has such a low capacity credit. Let's look at what Eirgrid had to say in 2009 :

However, the benefits [of wind energy] tends towards saturation as wind penetration levels increase. This is because there is a significant risk of there being very low or very high wind speeds simultaneously across the country. This will result in all wind farms producing practically no output for a number of hours (note that turbines switch off during very high winds for safety reasons). In contrast, the forced outage probabilities for all thermal and hydro units are assumed to be independent of each other. Therefore, the probability of these units failing simultaneously is negligible [Eirgrid 2009].

What they mean is that a gas power plant (CCGT) of 400MW might drop out but will do so independently of another gas plant. So that would be a loss of 400MW which standby reserve would adequately replace. But wind farms do not act independently of each other.  Instead, when one drops out, chances are the rest of them will aswell. So now you have a huge hole in generating output of about 1,900 MW, equivalent to about 50% of tomorrow's demand. So you need to have about 5 large gas plants ready to step in. Starting these type of plant up from "cold" is not a good solution as engineers have stated that this is 20 times more damaging to plant than "warm" starts. It is also very expensive and high emitting in pollutants. So gas plant are kept running on low load behind the wind and will then step in tomorrow to pick up the load as wind slackens off. 

Eirgrid are lucky in that the wind is forecast to decline over a period of 16 hours. What would happen if they are wrong and it falls off at a quicker rate ? Then they may need more fast acting plant like diesel or open gas cycle turbines. These are more polluting than efficient CCGT type plant and will result in higher emissions, thereby negating some of the benefits of having all this wind generation. 

Can we close down any of our power stations and replace it with a huge fleet of wind turbines ? Can we really make a transition to a more sustainable "green" based energy supply ? 

As you can see from the above, the answer is no, not with wind farms.

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.