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Risk to Electricity Supply

As consumers, we take a properly functioning electricity supply for granted, barring strong winds or snow bringing down power lines. But in practice there will always be some risk to the security of this supply. The question is: what is a realistic target to set for this risk?

In July, National Grid (NG) published their Future Energy Scenarios paper (FES 16) which put forward four scenarios of future energy demand for GB between now and 2040, and how those demands could be met.  It did not, however, quantify the risk to security of supply implied by the scenarios.  We assessed the risk of power outages occurring for each scenario and compared that risk to the standard used for planning before privatization of the electricity industry. At that time, the acceptable risk was considered to be a failure of the grid to meet peak demands during no more than four winters each century (a 4% chance of failure).

Apart from privatisation, the big change in recent years has been the appearance of wind farms across the country (and out at sea) and fields and house roofs covered with solar panels. Both these sources of renewable energy may have their part to play, but they cannot deliver the 24 hour a day, seven days a week output of conventional power stations fuelled by gas, coal or nuclear power.

Available-on-demand electricity is known as despatchable power in industry parlance. We did the same statistical analysis as was carried out before renewable energy became a significant part of the overall generating capacity by combining the probability curve for intermittent generation with that for despatchable generation.  We also made allowance for the actions the System Operator can use to reduce demand for short periods at peak time, such as reducing voltage and/or frequency of the AC supply. 

We found that wind generation can make a small contribution to meeting peak demand. However, it is intermittent – on-shore wind has a load factor of less than 30%, off-shore slightly more – and so the output at any point in time cannot be guaranteed. On the other hand, we know exactly what solar energy can contribute to peak demand on dark winter evenings: precisely nothing. 

One way that domestic electricity supplies can be supplemented is by drawing on surplus capacity from neighbouring countries such as France and the Netherlands. We looked at the situation both on the basis that Interconnectors to continental Europe would deliver power at times of peak demand and also with no Interconnector Allowance. 

This seemed prudent, since at present there appear to be no firm contracts in place for European Generators to deliver to Great Britain (Northern Ireland has a separate supply grid). Although other countries would be happy to sell us their surplus, they would certainly not compromise their own consumers if their output was struggling to meet demand. There is also an urban myth that ‘the wind is always blowing somewhere’. Quite possibly, but not necessarily across Europe: North European renewables share similar intermittency patterns to those of the UK.

At present, all the scenarios indicate that the current risk can be contained to about 4% by the use of Operator action to reduce peak demands, assuming we could draw on supplies from continental neighbours.  However, this risk will increase to between 12% and 19% by 2020, a totally unacceptable level of service.  The risk falls after 2020, but to limit the risk in the period up to 2025, we need to build five or more large gas-fired power stations. Even this may be optimistic if interconnector allowance is insufficient.

As we might expect, the risk to security of supply increases dramatically if we cannot rely on backup from the Continent.  Currently, the risk would be about 10%,  rapidly increasing to be between 45% and 60% by 2020.  And this would not be a short-term problem. The risk would remain high through to 2040. 

This situation would be intolerable in a modern society. GB needs to take urgent action to secure supplies, either through firm contracts with neighbouring countries or by building a significant number of efficient new gas-fired power stations. Subsidising the building of even more wind farms would do little to solve the problem: we would need vast numbers of turbines to meet peak demands.

We have based this analysis on the historical 4% risk factor, but even this may not be adequate. In the 1950s, a blackout would have caused inconvenience, but the consequences for communications, banking, security and business systems now could be incalculably greater. This is a major challenge that the country has to address urgently.


Dr. Capell Aris                                                                        Colin Gibson

The Scotsman - October 2016