The long overdue commissioning of the WesternLink Anglo-Scottish subsea interconnector, completed earlier this month, appears to be mitigating the need to constrain off Scottish wind power, but the delay in the cable’s delivery has meant that it has been overtaken by overall growth in wind on the network, and constraint payments continue, with over £2m being paid out to forty wind farms yesterday, the 23rd of October 2018, with an average price of £69/MWh, well above the lost income of £45/MWh.
Nevertheless, the WesternLink does appear to be facilitating very high, record-breaking levels of wind on GB’s electricity system. For example about 11 GW of wind was carried over a single settlement period (SP 41 which covers the period 8:00- 8:30 PM) on the 23rd of October 2018. This can be seen clearly in the two figures below, generated from REF’s free, online fuel mix database, which is based on Nationall Grid data. The first panel shows the total fuel mix, and the second panel the renewables and interconnectors alone.
Nevertheless, in spite of the high levels of wind actually facilitated, constraint payments are still very significant, particularly between midnight and 8am, when demand is low. For instance, in Settlement Period 1 on the 23rd, just after midnight, GB transmission system demand stood at 22 GW, while total wind was approximately 10.8 GW, of which 8.4 GW was actually used, with some 2.4 GW constrained off at a cost of £86,000 for that half hour period. Without constraints there would have been about 50% wind on the system.
It is interesting to note that the interconnectors to France and Holland were acting as import channels at this time, with a total of 1,660 MW, a reminder that the system and its markets are not, and probably never can be, made infinitely flexible in the interest of accommodating wind.
National Grid had earlier predicted a Balancing Services Use of System (BSUoS) cost of £2.11/MWh for the 23 October 2018, and it will be interesting to see if these forecasts, which reflect expectations for the WesternLink, are accurate.