Constraint payments to wind farms in the United Kingdom totalled £7.12m over the weekend, 28–29 July 2018, making it the most expensive weekend to date and well above the previous record of £5.87m for 24-25 June 2017. Constraints on Saturday the 28th of July amounted to £4.41m, and on Sunday the 29th to £2.71m.
The total volume of electricity curtailed was also a UK weekend record at 81.51 GWh. That is equivalent to the annual consumption of electrical energy of about 20,000 households.
The number of grid-connected (Balancing Mechanism) wind farms receiving payments for cutting output was also a record at 56 onshore (55 in Scotland and 1 in Wales), and 13 offshore.
When wind farms are constrained, this can be a fraction of the output of which they are capable at the relevant period. Over the last weekend, however, some 67 windfarms were 100% constrained, i.e. were completely shut down, at some time period, mostly between 10pm and midnight (Settlement Periods 44-48) on Saturday night.
Interestingly, while onshore wind in Scotland continued to provide the bulk of these constraints, at 70% of the money and 81% of the energy, offshore wind in England cost the consumer £1.75m to constrain off, accounting for 25% of the UK–wide cost. English offshore wind, however, accounted for only 15% of the energy discarded, reflecting the very much higher prices paid to offshore wind due to the higher lost subsidy, though, as with onshore wind, the constraint payment prices paid actually exceed the lost income by a considerable margin.
Table 1. Onshore wind farms in receipt of constraint payments over the weekend 28–29 July, 2018. Variations in the subsidy per MWh foregone reflect the different RO bands, where older windfarms receive 1 ROC per MWh and new windfarms receive 0.9 ROC per MWh. The value of a ROC is assumed to be £50 per MWh.
| Onshore Wind Farm | Constraint Payment | Energy constrained off (MWh) | £/MWh constrained off | Subsidy foregone £/MWh |
| Clyde | £758,113 | 10,911 | £69 | £50 |
| Whitelee | £535,231 | 7,802 | £69 | £50 |
| Crystal Rig II | £261,373 | 3,044 | £86 | £50 |
| Kilgallioch | £201,482 | 1,501 | £134 | £45 |
| Griffin | £196,971 | 2,914 | £68 | £50 |
| Fallago | £194,552 | 3,003 | £65 | £50 |
| Dunmaglass | £132,162 | 2,116 | £62 | £45 |
| Arecleoch | £131,120 | 1,983 | £66 | £50 |
| Aikengall | £123,019 | 1,267 | £97 | £45 |
| Bhlaraidh | £120,359 | 1,927 | £62 | £45 |
| Brockloch Rig | £110,463 | 1,293 | £85 | £45 |
| Farr | £108,740 | 1,528 | £71 | £50 |
| Black Law | £103,571 | 1,522 | £68 | £50 |
| Strathy North | £102,271 | 1,637 | £62 | £45 |
| Beinneun | £96,757 | 996 | £97 | £45 |
| Baillie | £94,467 | 972 | £97 | £50 |
| Camster | £94,090 | 1,009 | £93 | £50 |
| Kilbraur | £92,903 | 1,253 | £74 | £50 |
| Pauls Hill | £91,356 | 1,050 | £87 | £50 |
| Hadyard Hill | £74,391 | 1,191 | £62 | £50 |
| Galawhistle | £68,421 | 846 | £81 | £45 |
| Rothes | £67,237 | 773 | £87 | £50 |
| Dersalloch | £66,791 | 1,075 | £62 | £45 |
| Millennium | £63,965 | 863 | £74 | £50 |
| Lochluichart | £62,988 | 806 | £78 | £45 |
| A'Chruach | £62,449 | 774 | £81 | £45 |
| Andershaw | £60,617 | 621 | £98 | £45 |
| Black Law Ext. | £55,953 | 901 | £62 | £45 |
| Blackcraig | £52,385 | 537 | £98 | £45 |
| Moy | £50,818 | 651 | £78 | £45 |
| Auchrobert | £47,733 | 641 | £74 | £45 |
| Whiteside Hill | £46,066 | 525 | £88 | £45 |
| Sanquhar | £40,847 | 411 | £99 | £45 |
| Mark Hill | £38,538 | 567 | £68 | £50 |
| Clashindarroch | £38,025 | 481 | £79 | £45 |
| Burn of Whilk | £37,470 | 470 | £80 | £45 |
| Edinbane | £35,997 | 436 | £83 | £50 |
| Ewe Hill II | £35,703 | 575 | £62 | £45 |
| Minsca | £35,345 | 429 | £82 | £50 |
| Carraig | £32,665 | 347 | £94 | £50 |
| Beinn Tharsuinn | £29,787 | 440 | £68 | £50 |
| Corriemoillie | £29,508 | 398 | £74 | £45 |
| Pen y Cymoedd | £27,302 | 275 | £99 | £45 |
| Foudland | £26,216 | 313 | £84 | £50 |
| Toddleburn | £26,072 | 384 | £68 | £50 |
| Dunlaw | £25,272 | 372 | £68 | £50 |
| Beinn an Tuirc | £24,593 | 363 | £68 | £50 |
| Corriegarth | £23,485 | 289 | £81 | £45 |
| Minnygap | £21,734 | 235 | £92 | £45 |
| Dalswinton | £20,547 | 250 | £82 | £50 |
| Tullo Ext. | £20,332 | 260 | £78 | £45 |
| Hare Hill | £19,189 | 309 | £62 | £45 |
| Freasdail | £17,842 | 216 | £83 | £45 |
| Tullo | £16,425 | 206 | £80 | £50 |
| Glen App | £16,080 | 259 | £62 | £45 |
| An Suidhe | £11,285 | 163 | £69 | £50 |
| Assel Valley | £10,634 | 143 | £74 | £45 |
| Crystal Rig III | £7,555 | 88 | £86 | £45 |
| Clachan Flats | £4,531 | 67 | £68 | £50 |
Table 2. Offshore wind farms in receipt of constraint payments over the weekend 28-29 July, 2018. Variations in the subsidy per MWh foregone reflect the different RO bands. See Notes on the Renewable Obligation for the different band values for offshore wind farms. The value of a ROC is assumed to be £50 per MWh.
| Offshore Wind Farm | Constraint Payment | Energy constrained off (MWh) |
£/MWh constrained off |
Subsidy foregone £/MWh |
| West of Duddon | £1,005,892 | 6,817 | £148 | £100 |
| Ormonde | £225,341 | 1,757 | £128 | £100 |
| Robin Rig East | £209,695 | 1,384 | £152 | £100 |
| Walney Ext. | £166,588 | 1,012 | £165 | £90 |
| Robin Rig West | £156,866 | 1,339 | £117 | £75 |
| Walney | £141,517 | 851 | £166 | £100 |
| Thanet | £72,807 | 542 | £134 | £100 |
| Race Bank | £40,758 | 283 | £144 | £90 |
| Barrow | £37,413 | 434 | £86 | £50 |
| Humber Offshore | £34,814 | 223 | £156 | £100 |
| Lincs | £15,742 | 100 | £158 | £100 |
| Gwynt y Mor | £5,752 | 36 | £159 | £100 |
| London Array | £4,047 | 27 | £151 | £100 |
| Westermost | £3,393 | 19 | £179 | £100 |
| Greaater Gabbard | £2,258 | 14 | £159 | £100 |