The most important requirement for electricity supply is security. The key issue is that electricity should be available to all consumers whenever they require it. Loss of electrical supply to isolated rural homes in the middle of winter is, quite literally, a life-threatening situation as would be the failure of water supply or sewage pumping in towns and cities. The energy policies of UK governments until the present one, which have been supported by the Scottish government, have led to the deployment of large amounts of wind generation. However this has not only failed to improve security of supply but on the contrary has severely damaged it.
The existence of sufficient, reliable local generation capacity to meet peak demand is the best way of ensuring security of supply. Scotland was well placed in this respect until Cockenzie coal fired power station closed in 2013. Peak electricity demand in Scotland, which occurs on weekday winter evenings, is around 6GW. In 2010 there was 8.4GW of coal, nuclear, gas and hydro capacity, a sufficient margin to ensure supplies even after the essential requirement of allowing for the largest generating unit being out of action. The transmission link to England was almost exclusively an export facility.
By 2015 however, with the closure of Cockenzie there is now a maximum of only 7.4GW of on-demand (‘dispatchable’) generation. This is not enough to guarantee meeting Scottish electricity demand without imports from England and indeed electricity has been imported on 162 days since 2012.
With the closure of Longannet, dispatchable capacity will be further reduced to well below peak demand.
The Scottish government’s answer to security of supply concerns has in the past been to cite the expansion of wind and solar generation. Solar however must be disregarded for security purposes as it is dark in winter at the time of peak demand. And we cannot control when the wind will blow or not blow. There is currently (March 2016) more than 7GW nominal capacity of wind generation in Scotland and enough in planning to bring the total to about 15GW. In estimating wind contribution to security of supply, DECC at one time used a figure of 7% of nominal capacity ('load factor') as reliable output, which would give current and possible future wind values of 0.49GW and 1.05GW, significantly less than the potential shortfall. In fact the 7% figure is a serious overestimate. At 5.20pm on 19th January 2016, one of the coldest days of this winter, total output from nearly 12GW of UK wind turbines was 70MW, an output of only 0.6% of nominal capacity when demand was at a peak of over 52GW. Wind load factors of around 1% regularly occur in January, the month of highest demand. So the links to England, which are due to be increased to 4GW in 2017, will become an essential facility for importing power at times of low wind and even moderate demand.
While simple arithmetic suggests that the proposed expansion of these links to England should enable imports to cover most eventualities including the outage of the largest generator, they will not be available until 2017, a year or more after the proposed closure of Longannet. Furthermore this assumes that power will in fact be available in England for export. But the proliferation of wind generation there also and the consequent continuing closure of coal and gas capacity means that the UK as a whole faces the same problem with a predicted minimum margin of supply over demand of just 5.1% for the winter of 2015-16. The crisis is thus a UK one, although exacerbated for Scotland with a lack of major dispatchable local generators.
While the above analysis shows the seriousness of the situation it does not take account of the increasing fragility of the Scottish system when exporting heavily from wind generators in the North over the long transmission lines to England and the consequent risk of widespread failure of supplies. In that event a serious consequence of the loss of Longannet would the unacceptable time required to completely restart or 'black start' the network. For this Scotland must rely on its own resources of dispatchable coal, gas and hydro. (Nuclear cannot be restarted rapidly after an enforced shutdown, and neither the wind turbines nor the new high voltage direct current interconnection with England can be restarted until the system is re-established.) Without Longannet, cobbling together the necessary capacity from Cruachan and small hydro stations could leave the entire country without electricity for at least a day and a half.
How have we got into this situation and how might we restore our security of electricity supply?
A predictable, but unpredicted, consequence of the proliferation of large amounts of subsidised intermittent generation such as wind has been that such generators can underbid conventional generation in the auction to supply the grid when the wind is blowing. If the gas and coal generators can only sell electricity at times of low wind then they cannot cover their fixed capital costs and operate at a profit. They are also burdened with EU and UK carbon taxes. The argument that Longannet's profitability is destroyed by grid connection charges is quite spurious. These apply to all generators and for Longannet, the claimed £40M annual connection charge costs are much less significant than carbon taxes which have recently been around £225M could amount to up to £400M if the station were able to operate at full capacity.
The enthusiasm of the all UK, and in particular Scottish, governments for renewables, encouraged by industry and 'green' lobby groups, was never tempered by a proper technical and economic analysis of the likely consequences. The simple fact is that in the absence of practical, economic large scale storage technologies, which do not yet and may never exist, a modest amount of intermittent and uncontrollable generation is tolerable but a large amount is a potential disaster. This lesson is being learned not only in the UK but also in Germany and Denmark where coal is providing an increasing share of electricity generation.
Proposed new interconnections to Europe and Norway could help the UK as a whole though not Scotland directly, but only if there is a firm contract to supply power, which seems unlikely to be available. While most of the time Norway has a large supply of hydro, the availability of this cannot be guaranteed in a dry season, and in any case any imports to the UK have to compete with the demands of Norway's own energy intensive industries and exports to Denmark and Germany. Surplus power in Europe is largely from Danish and German solar and wind generation. This would be unavailable precisely at the same times as UK solar and wind. The claim that 'the wind is always blowing somewhere' is simply untrue when applied to north western Europe. France, whose hitherto reliable nuclear capacity is not being replaced and may actually be run down, has indicated that continuing supplies over the existing 2GW link cannot be guaranteed after next year.
Is there a way out? Having got oneself into a hole, the first thing to do should be to stop digging. The present UK government's withdrawal of subsidies for onshore wind and effectively for solar is thus a sensible start. Solving the problem in a purely Scottish context is not really sensible and is anyway unlikely to be possible as energy policy is not a devolved matter. However stopping any further consent for wind and solar would be a wise move. Enough is already consented to provide, on average, more than 120% of Scotland's electricity requirements. Proposed developments heading for the planning system include a number (such as the Fallago Rigg extension) in areas where grid congestion already results in substantial 'constraint payments' to operators to stop generating when the system cannot handle their output at times of high wind. It would seem particularly sensible to stop these.
The SNP government says that it will use devolved control of planning to prevent the construction of new, intrinsically safe, nuclear plant while (wisely as happens) being content for the ageing Hunterson reactors to continue operation. However, if the UK is to move to effectively carbon-free electricity in the future new nuclear is the only feasible route. The Westinghouse inherently safe reactor, designed when Westinghouse was UK owned, is being built successfully world wide and would offer an excellent way forward to replace Hunterston and provide Scotland with reliable all weather generating capacity.
Sir Donald Miller, FREng (Retired Chairman, Scottish Power)
Jack Ponton, FREng (Emeritus Professor of Engineering, University of Edinburgh)