DECC publish an inventory of UK power generating assets annually in table dukes5_10. I discovered recently that prior years are not deleted but are hidden and easily accessible on the spread sheet for years back to 2004. This post compares 2004 with 2015, allowing the evolution of UK power generation to be examined.
A summary of dispatchable power is shown in Figure 1. While the amount of nuclear, coal and gas generation has changed significantly, the total dispatchable power has changed hardly at all, decreasing by 2.1 GW from 70 to 67.9 GW.
With peak winter demand of the order 55 GW there appears to be ample capacity margin of dispatchable power. 67.9-55 = 13 GW margin = 24%.
Figure 1 Nuclear capacity has declined by 2.64GW, coal capacity has declined by 8.21GW these partly offset by CCGT capacity that has grown by 6.77GW. Import capacity via inter-connectors has grown by 1GW and is included on the assumption that the UK will have access to 3GW of French nuclear. Hydro has added 60MW and biomass 833MW. The details of power stations opening and closing are tabulated towards the end of the post.
What is the Blackout Risk?
A blackout occurs when a large segment of the power distribution network fails leading to the lights going out. There can be 3 principal causes for this happening:
- System engineering failure that may be caused by a nuclear power plant tripping out, instability caused by highly variable renewable power or a storm bringing down a power line.
- System capacity failure, where demand exceeds supply, and power needs to be cut to a chosen area to protect the remainder of the system.
- System fuel failure, where for example the UK runs out of natural gas, leading to a capacity failure.
 is a relatively common occurrence. There are grounds to believe that ever higher levels of wind penetration may lead to increased risk of engineering failure in future. The UK has come close to  in the recent past as natural gas supplies were strained by a combination of factors such as the closure of the Elgin platform and the Fukushima nuclear accident in Japan. The sport of blackout speculation normally focusses on . Since unforeseen outages are common place, all countries have a capacity margin in place as contingency, and the speculation recently has been that the UK capacity margin is now wafer thin. The data at face value quite simply do not support this contention.
When is the Blackout Risk?
UK power demand follows three cycles of daily, weekly and annual duration. It is when the peaks of these three cycles are coincident that UK meets its annual demand peak. It is at that time the risk of capacity failure is greatest. Demand is always highest at around 6pm, it is always higher Monday to Friday than at the weekend and it is always higher in winter – December to February. Therefore, risk of capacity failure will always be at around 6pm, on a weekday in winter. At all other times, demand does not press the capacity margin. In January this year, peak demand was 53.5 GW at 17:30 on Monday 19th.
Renewables and Averting Blackouts
Figure 2 includes data for solar and wind capacity. Solar we know can never contribute to averting a capacity failure in the UK since it is normally dark across the UK at around 6pm in winter when electricity is needed the most. Wind is a wild card. It is just as likely to be flat calm everywhere as it is to be windy. From 26th September to 4th October wind contributed virtually nothing to UK power supply. Since it cannot be relied upon, dispatchable capacity must be kept in reserve and paid for and this is why there has been virtually no change in dispatchable capacity in the UK since 2004.
Figure 2 Same as Figure 1 but with renewable capacity added.
Renewables, however, do displace gas and coal generation, and in so doing, fuel stores can be preserved during winter reducing the risk of  system fuel failure.
The Changing Face of Generation
Figure 3 Since 2004, four of the UK’s ageing Magnox reactors have closed. Wylfa is the only remaining Magnox reactor and is scheduled to close in December of this year. 2.64GW of nuclear capacity has been lost.
Figure 4 Since 2004, six large coal power stations have closed (Cockenzie, Didcot A, Floots point, Ironbridge, Kingsnorth and Tilbury B) with the loss of 8.2GW. Note that Ironbridge has converted to biomass with reduced capacity of 360 MW.
Gas – CCGT
Figure 5 The UK’s large fleet of CCGTs has seen a number of old small units close and some large modern units open. For example Pembroke (2.18GW), Staythorpe C (1.77GW) and West Burton (1.33GW). In total 6.77GW cpacity has been added.
Figure 6 The UK has a large number of small hydro schemes. While several new schemes have opened, two quite large old schemes have closed, Kinlochleven (30MW) and Fort William (62MW). Both schemes were linked to Aluminium smelters and I presume they may re-open to provide domestic electricity supply. The only new large hydro to open is Glendoe (100MW).
Wind and Solar PV
Wind and solar capacity was effectively zero in 2004. Different sources provide rather different figures for 2015 as detailed in Figure 7.
Figure 7 Installed wind and solar capacity in the UK from various data sources.
For the sake of consistency it is the dukes5_10 numbers that are plotted in Figure 2 but they do seem to underestimate reality. The Renewables UK and Renewable Energy Foundation (REF) numbers seem to be closely alined for wind. The latter are based upon subsidy uptake and are likely to be the most reliable. But when it comes to securing electricity supplies at 6 pm on a weekday in winter the difference between 16.3GW (DECC) and 20.4GW (REF) is neither here nor there. On many days each year, the actual generation from these sources will be effectively zero at the time of need.
During review, Roger Andrews sent this chart (Figure 8) from National Grid. It correctly assumes that all power stations may not be available at the time of need and that is why a capacity margin is required.
Figure 8 Derated capacity margin for UK power generation from National Grid.
There are four main points to me made from this post:
- Dispatchable capacity in the UK has declined 2.1GW since 2004 which is not a material difference since electricity demand has also fallen in that period.
- The nameplate capacity margin is approximately 13 GW which seems ample contingency for plant outages. Increasing this margin would involve paying companies to keep higher unused capacity in reserve.
- The risk of capacity failure is always around 6pm on a weekday in winter and only lasts for a few hours each day.
- 13.5 GW of wind and 7 GW of solar cannot be relied upon to provide any supply at 6 pm on a winter week day when the blackout risk is greatest.