Renewable Energy Foundation

Large volumes of wind energy are being discarded in Scotland in order to preserve grid stability, with a fleet average of over 13% of generation constrained off in the years 2015 to 2021, inclusive, with a high of 19% of generation in 2020. Some wind farms have been discarding between 20% and 50% of their output, while being rewarded with generous constraint payments from the electricity consumer for doing so. The reductions in environmental benefits are not given adequate weight in the planning system, where the low marginal benefit of additional wind capacity appears to be poorly understood. This blog offers detailed data on the volumes of wind energy constrained off at a fleet level in Scotland between 2010 and 2021, and for every individual wind farm in 2020 and 2021.

Figure 1: Part of the Monadhliath Mountains, with Creag Mhor overlooking Loch Gynack in the foreground.  By Spike - Own work, CC BY-SA 4.0, Link

Wind turbine generation has been weak in 2021 due to low wind conditions, with total (onshore and offshore) output reduced by about 14% in 2021 as compared to 2020 (61 TWh estimated in 2021 as compared to 72 TWh in 2020). Onshore wind output has been the most severely affected, with a reduction of 20% in 2021 (27 TWh estimated) as compared to 2020 (34 TWh).
This has had a significant effect on the volumes of wind energy constrained off the system, with a corresponding and welcome reduction in the total cost to consumers.

In 2020 constraint payments to onshore wind in Scotland amounted to 3,460 GWh (at a cost of £243m), whereas in 2021 this was 1,783 GWh (at a cost of £107m), a reduction of 48% by volume of energy.

While it would be reasonable to say that grid reinforcement and the somewhat improved reliability on the Western Link interconnector account for part of this reduction in constraint payments and volumes, the majority of the effect is the result of reduced wind power output, which reduces the need for wind to be constrained off the system. This reduction in output affects individual wind farms in a way that is highly significant from several perspectives.

Firstly, the average load factor of Scottish onshore wind farms has fallen from 26.7% in 2020 to 22.1% in 2021. This is the second lowest fleet load factor in 20 years, the lowest being 21.5% in 2010. A reduction of this magnitude has implications for the wind farm’s Internal Rate of Return (IRR), a shortfall that may be difficult for the investors to recover without exceptional output in the future, exceptional output that probably lies beyond the end of their economic lifetimes for older and even middle-aged installations. This will have implications for the way that investors view the future of these assets, particularly older sites where maintenance costs are rising.

Secondly, the reduction in output in 2021 is a substantial contributor to the current energy bills crisis, having caused the electricity system to draw heavily from gas fired generation at precisely the moment that many other systems in Europe were experiencing the same problems. This has combined with high international demand, particularly in Asia (which is reducing greenhouse gas emissions and local air pollution by switching from coal to gas) to drive particularly high prices of natural gas in the European region.

This effect may have come as a surprise to many renewables supporters, who expected that large wind fleets would buffer the United Kingdom against high gas prices. In fact, as is well-known to experienced analysts and has been long-predicted, a heavily renewables-based system becomes critically dependent on natural gas generation across all timescales, from seconds to years, in order to guarantee security of supply. The volume of gas consumed may fall, but, paradoxically, the exposure to gas and its price increases. The addition of more wind power will do little or nothing to mitigate this effect, and will all but certainly intensify the problem.

Thirdly, the reduction in constraint volumes brings into sharp focus the low marginal benefit of adding further wind capacity in Scotland. A reduction in wind power output, such as that in 2020, reduces constraint payments. Therefore, conversely, any new proposal for wind power in Scotland, which increases potential output, must be expected to increase constraints. Additional capacity therefore has a high probability of some part of its own output being constrained off, reducing the global environmental benefits it can claim to offset local environmental harms. This matter should obviously be given close scrutiny in the planning balance by decision makers. However, and as far as we are aware, the Scottish Government has not issued formal advice requiring Reporters to take the matter into account.

The constraints problem will persist until there is more than sufficient interconnection between Scotland and the centres of demand in England. Given the Scottish Government’s plans for wind, particularly offshore, it is not clear that the required level of interconnection is either feasible or economically viable. Constraints are therefore likely to persist for the foreseeable future, with wind capacity constantly outrunning the network’s ability to transport it to consumers at reasonable cost.

The tables below provide detailed figures on the degree to which Scottish wind farms are discarding potential generation, all the information being based on our own datasets as collected from official market sources. The first table provides our calculated estimate of Scotland’s wind generation output by year, the level of actual constraints in those years, and a calculation of the proportion of wind energy that has had to be discarded to preserve grid stability. The second table provides similar estimates of generation and discarded energy for each individual wind farm in both 2020 and 2021.

The headline findings from these tables are stark. On an annual basis since 2015, when the wind fleet reached substantial levels, Scotland has been discarding around 13% of all wind energy that it could have generated. This figure rose to a high of 19% in 2020, when demand fell due to lockdown and other public health measures, before falling back to 13% in 2021, a low wind year with recovering levels of consumer demand.

It follows that decision makers in the planning system should expect that if a wind farm currently applying for consent has not taken the potential for constraints into account, it is likely to have over-estimated its actual benefits of generation by between 10% and 20%, figures that could be crucial in determining the planning balance given the significant adverse local, and even regional environmental impact of many wind farms, on wildlife and the landscape and visual quality of unspoiled wildland areas.

However, the results on a site-by-site basis indicate that a general figure may not give an adequate insight into the scale of potential losses. Some wind farms in 2020 discarded extremely high fractions of their potential output. Corriegarth, for example, lost about 51% of its output to constraints, with other notable sites being Strathy North (48%), Blaraidh (47%), and Farr (39%). Even some of the largest, high-profile sites in lowland areas had to discard substantial proportions of their output, such as Whitelee (31%), and Fallago Rig (27%). Strikingly, these proportions remained very high even in 2021 and in spite of the facts of weaker winds and higher demand. In this year, Dorenell discarded 35% of its output, and Strathy North 28%, Bhlaraidh 24%, Farr 22%, Whitelee 17%, and Fallago Rig 15%.

It should be noted that many of the heavily constrained wind farms are located in areas with great ecological, environmental and wild land value. One such area is the Monadhliaths, Great Glen region adjacent to Loch Ness. This region is one of Scotland’s most remarkable wilderness areas, known for the unaltered antiquity of its landscape and its austere beauty (see Figure 1 above). Nine large wind farms have been built in this remarkable wild land area (see Figure 2 below). All of these received constraint payments in 2020/2021 with an average of 22% of potential output being discarded, averaged over the two years at a total cost to the consumer of £67 million. In spite of the clear economic evidence that the site is saturated, there are seven further wind farms in that location going through the planning system, which could increase the installed capacity by 66%. ;four already with permission to build and three awaiting a decision. It seems that the planning process is failing to consider the multiple harms to the public interest incurred by developments which sacrifice an irreplaceable natural landscape for consumer-subsided wind farms whose output is capped – at a further cost to the consumer – because the site is a wilderness remote from where power is required.

There can be no serious doubt that this is an important issue for the planning system and that it needs to be addressed to preserve public confidence in the rationality of decisions taken by reporters and the Scottish Government.

Figure 2: Wind farms are indicated by circles whose area is proportional to their installed capacity. The nine operational and constrained wind farms as of 2022 are labelled and coloured red.  The four wind farms with planning consent are the blue circles and numbered as follows :  Glen Kyllachy (1) 50 MW; Aberarder (2) 50 MW; Dell (4) 42 MW; Millennium South (3) 35MW. The three wind farms whose planning permission has not yet been determined are identified by yellow circles and are: Corriegarth II (5) 76 MW, and Cloiche (6) 150 MW and Glenshero (8) 168MW. Note that both Cloiche and Glenshero are each effectively split over two locations west and east of the centre of Stronelairg.  The areas of the pairs of circles numbered 6 and 8 are proportional to the relative sizes of the west and east parts of the proposed Cloiche and Glenshero wind farms.

Table 1: Annual electrical energy generated and constrained at all Scottish wind farms, 2010 to 2020. The generation data is derived from monthly Renewables Obligation (RO), Contracts for Difference (CfD) and Renewable Energy Guarantees of Origin ( REGO) data for Scottish wind farms as reported in the REF databases. As of the date of publication of this blog, the generation data for 2021 is not complete for all generators. However, for those wind farms where there is generation data for a month, the constraints volumes for that generator and month are also included in the totals below to ensure consistency in calculating the percent of output that is discarded in 2021.