Over 40% of Wind Energy Shutdown Last Night

by OWEN MARTIN

Last night, over 40% of wind energy produced was shutdown or curtailed during a spell of gale force winds across the island of Ireland. This episode clearly shows the limitations of relying too much on an intermittent source of energy like wind. Billions of euros worth of turbine installations become worthless at both low wind and at high wind.   

Figure 1

The reason for the shutdown of so many wind turbines can be clearly seen in the System Frequency charts before and after the wind shutdown. 

As the gales gathered in strength on Sunday evening, maintaining the frequency of the grid became more difficult :

Figure 2

The zig zag patterns in the Figure 2 show how frequency fluctuated between 49.9 and 50.1 Hz. The dips represent periods of too much wind when system inertia drops (due to lack of conventional generation such as coal or gas). Should frequency drop below 49.7 Hz then a blackout may occur, so Eirgrid rectified this by shutting down some of the wind and allowing more conventional generation into the system. The frequency then rises again to 50Hz. Gas turbines are forced to ramp up and down more often to maintain system stability during such periods thus pushing emissions up and negating some of the benefits of  having all the wind in the first place. 

Figure 3

Figure 3 shows what happened when over 40% of the wind output was shutdown and there was more manageable levels of wind, in this case about 1,500MW. The frequency is very stable and there is little risk of blackouts. This has been normality in the grid for many years. Compare it with Figure 2. This is the future. It will certainly test engineering skills to it's limits. Gas turbines will have to function under greater strain than before. It will cost a lot of money. There can no longer be a guarantee that the electric kettle will boil when you want it to. 

The other option Eirgrid have to maintain a stable frequency in these situations is to cut demand - which is in effect a blackout under another name. The future is renewable. The future is green. I'm at a loss to figure out how this is "progress".

Rising Costs of Stabilizing Irish Grid

Synchronous Condenser in Australia (Wikipedia)

As levels of wind energy increase, fossil fuel generators and other devices are been called on to provide stability services to the Irish grid to help prevent blackouts. Its a simple engineering fact that as wind energy increases, the grid loses inertia and the frequency of electricity sent to your home becomes more difficult to control. The frequency of the Irish grid is set at approximately 50 Hertz, give or take about 1 Hertz, and all our appliances will not run outside this small range. 

Large power stations have trip switches that deactivate generators when the frequency moves outside this range so if the grid loses inertia for even a few seconds, there will be a cascade effect as generators drop out. A widescale blackout is the likely result. The rotational speed of wind farms is changing all the time and at different regions and it's because of this that they can't provide inertia to the grid. Gas and coal power stations are classed as synchronous generators because they provide stability to the grid, while wind farms and the East West interconnector are deemed non synchronous generators (SNSP). 

At the moment non synchronous generators are limited to 50-55% penetration in the grid. It is envisaged that this will have to rise to 75% in order to achieve the 20-20 targets. A consequence of this will be less synchronous generators online during high wind periods and increased risk of blackouts. So synchronous generators need to be paid more to maintain stability through what are called ancillary services.     


The diagram below shows that these ancillary or grid stability payments increased from € 24.5 million to € 26 million in the year to April 2016. 

POR means Primary Operating Reserves and SOR Secondary Operating Reserves. POR can step in up to 5 seconds and SOR up to 15 seconds to replace a generator that suddenly drops out. Tertiary Reserves (TOR1 and TOR2) take longer to start but can be maintained for longer time. These reserves are set by the single largest generator that happens to be online at the time, usually the East West Interconnector. However, demand for fast reserves, which are inefficient and high emitters, is increasing with higher levels of wind as wind fluctuations dominate the grid. 

The largest increase was for Reactive Power services. These are mostly provided by synchronous condensers which are able to provide stability in times of large voltage changes due to stochastic wind energy. Engineers at UCD provide a good overview of these devices here.  

Like battery storage units, synchronous condensers are net consumers of electricity but are essential for keeping the lights on with high levels of non-synchronous wind energy.  Adding units that consume more energy over their lifetime that they can generate is a consequence of the wind program and should have been included in a cost benefit analysis, which as we know, was never done.

What about alternatives ? Well, biomass and hydro provide synchronous power as of course does nuclear power. But green lobby groups do not want these and wind lobby groups want us to install more wind, this time offshore. Surely, it's time we looked at other options.

Sources:

1) http://www.eirgridgroup.com/site-files/library/EirGrid/AS_OSC_Report_April2016.pdf

2) http://www.eirgridgroup.com/site-files/library/EirGrid/AS_OSC_Report_2014_2015_Nov.pdf

3) http://www.eirgridgroup.com/site-files/library/EirGrid/OperationalConstraintsUpdateVersion1_35_February_2016.pdf

4) http://erc.ucd.ie/wp-content/uploads/2013/10/IRC_P%C3%A1draig_Daly.pdf