Reactor 1 (600 MW) of the Torness nuclear power station in Scotland tripped at 09:00 on 22nd November whilst reactor 2 was on half load for refuelling. Since then Scotland has been dependent on electricity imports from England for every hour of every day peaking at 2552 MW at 20:00 on 23 Nov as the mercury plunged towards -5˚C. At that point, Scotland was dependent on England for half of its electricity. In the past, Scotland was always 100% reliant on home-grown power.
In March of this year Scottish and UK government energy policies that are founded on Green thinking conspired to cause the closure of the 2.4 GW Longannet coal fired power station in Scotland that was the beating heart of the Scottish grid. In anticipation of this event Leo Smith at Gridwatch began to monitor electricity transfers between England and Scotland as reported by National Grid with the data series beginning on 30 December 2015.
On the charts below, Scottish wind output is modelled as 0.4*UK wind, data from Gridwatch. This is based on installed capacities and is far from perfect since at certain times it may be windy in Scotland and calm in England and vice versa. The 5 minute resolution Gridwatch data has been averaged to 1 hour resolution.
Figure 1 shows electricity transfers in blue and wind production in red for January and February 2016. This is before Longannet was closed. Some key observations:
- Scotland was an exporter of electricity to England for virtually the whole of this two month period with only a handful of incidences where trivial imports occurred.
- Wind production appears to have reached a plateau at around 3500 MW suggesting this is some sort of curtailment level, bearing in mind this is pro-rated from UK data. Pro-rated Scottish wind never gets above 62% of installed capacity.
- Curiously, electricity exports have this same 3500 MW export plateau. The 4800 MW inter-connector capacity may have an effective de-rated capacity of 3500 MW.
- There is a correlation between wind output and Scottish exports. An argument can be made that most of Scotland’s wind output is simply exported to England. If I were living in the Scottish borders gaping at wind turbines everywhere, I would be particularly furious about this point.
- If the derated capacity of the inter-connectors is 3500 MW, this might explain why wind is curtailed to this same value.
Figure 2 shows the picture for October and November (to date) 2016. This is the first data for winter months post Longannet closure. The key observations:
- Scotland has become a serial electricity importer as was to be expected. In Jan-Feb imports were 2,733 MWh. This has risen to 227,002 MWh in Oct-Nov (to date), an increase by a factor of 83.
- Imports of 1000 MW or more are commonplace peaking at 2552 MW on 23 November following the reactor trip at Torness.
- Oct-Nov was less windy than Jan-Feb, which was particularly stormy and wind never got close to the presumed 3500 MW curtailment level (dashed line lower panel). However, exports seem to be curtailed at a lower level of 2600 MW. This is difficult to explain other than wind did not get above this level.
- Exports and wind output are still correlated but with one notable exception. From 11 to 17 Nov there was a block of exports not correlated with windy conditions. We can speculate that it was windy in Scotland but not in England at this time.
- The reactor trip at Torness was followed by a sudden fall in wind, which just goes to show how events can conspire against grid integrity.
Figure 3 shows how Scottish exports have fallen by a factor of 2.4 from Jan-Feb to Oct-Nov. This number is impacted by Jan-Feb being particularly windy. Imports have risen by a factor of 83. In a normal world, swings in export and import dependency of this order would be viewed as catastrophic. But shrouded by the cognitive dissonance of Green thinking, its quite acceptable for Scottish Government policy to create this outcome.
Figure 4 In my earlier post called Blackout I laid out a scenario where 50% of Torness and 50% of Hunterston B nuclear power stations were off line (one reactor down in each station) and that owing to a prolonged wind lull, pumped storage was empty. This created a 1945 MW import call on England. I didn’t expect these circumstances to arise so soon. Current events have in fact led to a larger import requirement of 2552 MW but this time England was able to answer, despite the 5 to 10 GW nuclear shut down in France. In fact, despite having so much power off line, and importing for much of the recent past from England, France is still exporting to the UK at times of peak demand.
One factor working in favour of the grid is that it has in fact been relatively windy despite the plunge in wind output on the 22 and 23 Nov (Figure 2). At 18:00 on the 22nd, wind was still 2099 MW and at 18:00 on the 23rd it was 1089 MW. The calm conditions that increase the blackout risk were absent and the generally windy nature of this episode means that storage can still be filled at night.