Electricity generation from wind power has grown dramatically in the UK in recent years (Figure 2) and so has the challenge to balance the grid, especially when it is very windy. One of the balancing tactics deployed by National Grid is to pay wind farms to switch off when it is windy. This cost, borne by the consumer, is called a constraint payment. In 2015, UK consumers forked out £90 million to pay subsidy driven wind farms to switch off.
The amount of UK wind that is constrained is growing with the level of penetration. At 10% wind penetration, 6% of the wind power available is constrained (Figure 9).
All of the data presented in this post are from the Renewable Energy Foundation (REF)  web site that provides a truly excellent database for UK power generation, especially renewables. REF provides daily, monthly and yearly figures for wind curtailment payments, the former behind a paywall. They were understandably reticent about me buying and then publishing their daily data, so this post is based on the public domain monthly data .
Let me begin with a look at total electricity supply that shows annual cycles with peaks centred in the winter months (Figure 1). But UK electricity supply (and demand) is falling. If we use electricity consumption as a marker of our level of civilisation and prosperity then this may give cause for concern.
Figure 1 There are many possible reasons for the decline in UK electricity consumption, among them 1) improved energy efficiency of appliances and homes, 2) high energy prices causing demand to fall and in some cases causing energy poverty, 3) offshoring of heavy industries and 4) embedded wind and solar generation that show up in statistics as reduced demand.
Figure 2 shows how metered wind generation has grown steadily: rapidly from 2011 to 2013 and more slowly since 2013. Only large wind farms are metered. Smaller wind farms and individual turbines are embedded in the low voltage transmission system and show up in statistics as reduced demand. Hence total wind generation is higher than shown here. In 2015, roughly 73% was metered and 27% was embedded .
Figure 3 shows how monthly average wind generation has grown as a percentage of total generation. The current record is 12.4% in December 2015.
Figure 4 shows that the amount of wind constrained has grown steadily but as we shall see this growth is not linear with wind generation (Figure 9).
Figure 5 shows wind constrained as a percent of total generation. In record production month of December 2015, 11.2% of wind generation was constrained.
Figure 6 shows that the cost of constraining wind has grown in line with the amount of wind constrained (Figure 4). The unit price has been fairly constant since 2013 (Figure 8).
Figure 7 In 2015, total wind constraint payments exceeded £90 million and have been increasing at around £30 million per year.
Figure 8 The unit price of constraint fell rapidly until 2013 but has since largely flattened out. In 2015, the average price paid to wind producers to not produce was £71 / MWh. I am uncertain if producers are also paid the Renewable Obligation subsidy of roughly £45 / MWh for not producing. That would bring the total to £116 / MWh. This is an interesting number since it is similar to the price where storage is considered to become competitive .
Figure 9 Finally in Figure 9 we get to the chart I want to show the most. Plotting percent wind constrained against percent penetration we see that problems absorbing wind onto a balanced UK grid begin at 3% penetration. Below 3%, little wind is constrained on a monthly basis, above 3% in certain circumstances, some wind is constrained. Above 6% penetration some wind is always constrained on a monthly basis. Constraint has grown along with the level of penetration but the relationship is unclear, r^2 for linear and exponential fits are similar at around 0.4.
In 2015 the UK consumed 283,092,000 MWh of electricity. At a retail price of £167 / MWh, the UK electricity market has a notional value of £47 billion per year. Against this backdrop it is to be anticipated that RE enthusiasts and the pedlars of wind power might argue that the £90 million spent on constraint payments is an irrelevant 0.2% of the market.
The real issues here are economic and social ones. Our economies thrive and are based upon efficiency and competitiveness. Here we have acceptance of £90 million being spent in a single year to pay heavily subsidised companies to not do what they are established to do and that is to provide low carbon electricity to the British people. This is Orwellian (or Soviet) economics of the worst kind. In 2015, £90 million pounds was transferred from the pockets of the poor to the pockets of the rich in order to sustain an unsustainable electricity production mirage.
The official Green / Government narrative says that at times of surplus wind production, it will be stored for use at times of scarcity. OR alternatively surpluses may be exported. AND a third option is to balance wind off hydro generation combing the two to provide dispatchable supply.
The reality is that little if any surplus UK wind is stored. The investment decision on the main but puny storage scheme at Coire Glas appears indefinitely delayed . Exporting surplus wind to Europe is a fantasy, not because we don’t have sufficient interconnectivity but because when it is windy in the UK it is also likely to be windy in Europe  hence there will be no demand for our surplus. Atlantic depressions are continent sized. And UK hydro is woefully under-dimensioned to have capacity to balance UK wind output. UK hydro is instead used to provide some base load and some diurnal load-following capability .
Hence, the official narrative is simply fantastical rubbish. The reality is that on windy days in the UK wind producers are paid by you and I to not produce their heavily subsidised electricity.
 Renewable Energy Foundation
 REF monthly constraint payments
 The Changing Face of UK Power Supply
 The Holy Grail of Battery Storage
 The Coire Glas pumped storage scheme – a massive but puny beast
 The Wind in Spain Blows
 Hydro Balancing Wind in the UK
Footnote added 14:00 on 5th September.
In the caption to Figure 8 I leave an open question about the exact structure of constraint and subsidy payments. Dr Lee Moroney of the Renewable Energy Foundation has provided this clarification:
The producers are not paid the RO but, in addition to the constraint payment, they do get whatever they would earn under their PPA for the constrained-off generation, i.e. something around the wholesale electricity price, so your point still holds. In other words, the constraint payment is just to compensate them for the RO foregone, and prior to August 2015, the LEC foregone, plus – we are told – the additional costs inherent in reducing output. We have struggled to understand how the latter can be as much as they have been. For what it is worth we have been told there are, for example, costs associated with the risk of not being able to power up again. We incline to think they are charging what the market will take. Ofgem is looking at the constraint price issue at the moment – see http://www.ofgem.gov.uk/publications-and-updates/extension-transmission-constraint-licence-condition and REF’s response to the Ofgem consultation at http://www.ref.org.uk/publications/332-transmission-constraint-licence-condition-consultation