With energy prices and energy policy very much in the news, it is timely to take a detailed look at the history of UK electricity production. The UK Department of Energy and Climate Change (DECC) are once again to be commended for compiling and making available a vast array of accessible energy statistics upon which most of the charts presented here are based. Those who want a more detailed understanding of how electricity delivery works may wish to read my earlier post: Electricity supply and demand for beginners.
Figure 1 Fuel types used in UK electricity generation. In the beginning there was only coal. And then from around 1956 nuclear and oil were introduced to the generating mix and the contribution from both grew significantly thereafter. In the early 1990s natural gas was introduced and expanded rapidly, replacing oil and a significant portion of coal. In the early 1990s, all of this gas came from the UK North Sea but since 2005 a growing portion of gas used in generation has been imported. The “Other fuels” category includes coke oven gas, blast furnace gas, waste products from chemical processes and refuse derived fuels. Wind and hydro make a tiny contribution. Data from DECC, spread sheet called Electricity since 1920 historical data.
Figure 2 is a similar picture to Figure 1 but shows instead the amount of electricity produced by each fuel type as opposed to the amount of fuel consumed. Of particular interest is the documentation of electricity used by the power stations. Unfortunately coal, oil and other have been lumped together in a “Conventional thermal” category by DECC, I imagine for good reason. Transmission losses and electricity imports are not shown. The subtle change in the shapes of the charts in Figures 1 and 2 are down to improving energy efficiency of power generation over the years.
Since electricity supply and demand must match, Figure 2 provides a picture of electricity demand growth and decline in the UK which may be divided into 5 discrete segments.
- 1920 – 1950 shows slow growth in electricity demand, fuelled exclusively by coal. This was the era of grid construction and the introduction of electric lighting to homes and factories.
- 1950 – 1973 was a period of rapid growth in electricity demand fuelled by a boom in demand for electric gadgets like televisions and in the manufacturing of those goods.
- 1973 – 1982 was a decade of stagnation. The Yom Kippur war of 1973 followed by the Iranian Revolution in 1979 and the Iran – Iraq war saw spikes in oil and energy prices that slowed economic growth.
- 1982 – 2003 saw renewed growth in electricity demand but at a slower pace than the pre-1973 period.
- 2003 – 2012 saw electricity demand plateau and then fall significantly. The beginning of this process coincides with the beginning of the bull run in energy prices. While energy efficiency gains may account for part of the fall in demand, high energy prices, fuel poverty and double dip recession are the principle causes.
In order to get a clearer picture of the contributions from individual sources, the following series of charts shows each source individually. All charts scaled to 250TWh per annum to ease comparison of relative importance.
Figure 3 UK power generation from coal, oil and other sources.
Figure 4 UK power generation by combined cycle gas turbines. Note how the fall in gas generation in 2012 is largely compensated by an increase in coal generation (Figure 3), presumably in response to fuel price changes.
Figure 5 UK power generation from nuclear energy. Nuclear output peaked at 90.6 TWh in 1998 and has since fallen with the closure of 2.8 GW of Magnox nuclear capacity and unscheduled outages but the performance of nuclear has improved dramatically since 2008 (see below). Since nuclear is on all the time, this creates a surplus of power at night when it is not needed. Part of this surplus is used to pump water up hill into mountain top reservoirs that are allowed to drain through a turbine when the power is needed most, normally at 6 pm the following day. The power used to pump water has been deducted from the power generated by nuclear. The power produced by pumped storage is effectively stored nuclear power.
Figure 6 Power generation by non-themal renewables which is dominated by wind and solar power. Renewables remain a tiny portion of the electricity generating mix, hydro is too small to be worth plotting. Renewables enthusiasts may point to how this chart resembles the trailing edge of the coal and nuclear as capacity was building in the early days. Renewables sceptics would point to the landscape harm caused by wind turbines and the high cost to date and that current infrastructure may need to increase 4-fold for renewables to make a significant impact. Solar has much smaller landscape impact and provides power during the day when it is most needed.
The following figures show the relative contributions of the main fuel types to the generating mix.
Figure 7 illustrates how king coal has dominated the UK generating mix since power generation and distribution began 100 years ago.
Figure 8 illustrates the dash for gas whose popularity has waned in the wake of competition from Japan for liquefied natural gas cargoes following the Fukushima nuclear incident.
Figure 9 more or less reflects Figure 5. Nuclear currently accounts for about 17% of UK electricity generated. This comes from 7 Advanced Gas-Cooled Reactors (AGR), 1 Pressurised Water Reactor (PWR) and one remaining Magnox Reactor at Wylfa.
Figure 10 The contribution of non-thermal renewables to the UK generating mix has now passed 6%. Note Y axis scaled from 0-10%.
Figure 11 The chart shows combined Nuclear, Hydro and non-thermal renewables. Low carbon power generation peaked in the 1990s thanks to the expansion of UK nuclear power. The sharp fall in low carbon power that followed by and large reflects the closure of the UK Magnox fleet of reactors. Low carbon generation has shown sharp recovery in recent years, due in part to improved performance of nuclear and in part to expansion of renewables.
Load factors and efficiency
The following 6 Figures (12 to 17) illustrate the load factors and thermal efficiencies of coal, gas (CCGT) and nuclear generation based on data from DECC table DUKES5_10. The load factor is a measure of actual power station output compared with total possible output. As detailed in Electricity supply and demand for beginners, it is necessary to ramp power stations up and down and to switch them on and off to accommodate daily, weekly and annual cycles in electricity demand. Thus, power stations are not on all the time and load factor is a measure of the percentage of time they are actually generating. Thermal efficiency is a measure of how efficient power stations convert the energy contained in the input fuel to the electricity output. The key observations are summarised at the end of Figures 12 to 17.
Figure 12 coal generating load factor
Figure 13 CCGT generating load factor
Figure 14 nuclear generating load factor
Figure 15 coal thermal efficiency
Figure 16 CCGT thermal efficiency
Figure 17 nuclear thermal efficiency
Understanding the data shown on the load factor charts is highly complex. What caused a switch from gas to coal generation in 2012? Here is a rough guess about what is going on:
- Expansion of North American shale gas production (mainly at a loss to the producers) has dumped natural gas prices on that continent leading to gas substitution for coal in power generation. Surplus US coal may have been exported to Europe, dumping prices.
- Japanese gas consumption, mainly liquefied natural gas (LNG) has risen in the wake of the Fukushima incident pushing up international gas prices everywhere, apart from N America.
- The swing in prices towards cheaper coal and more expensive gas is reflected in the market driven generating choices made in the UK.
- Closure of old (emissions non-compliant) UK coal plant has reduced coal generating capacity. Remaining capacity will get higher utilisation.
- CCGT, the most efficient and least CO2 intensive form of fossil fuel generation is the big loser.
- The owners of CCGTs are caught in the vice of falling utilisation combined with rising fuel costs. The response could be to raise electricity prices.
- Nuclear tends to be on 24/7 and the slump in load factor towards 2008 reflects unscheduled outages. The problems underlying this seem to have been resolved and nuclear reliability is rising back towards historic highs of 80%. But the reactor fleet is ageing and so it is reasonable to expect this trend to turn down again, some time.
I don’t think there is any way that market or government analysts could have foreseen the turn of natural and market driven events that has led this development of UK power generation that seems counter to policy. The efficiency charts are fortunately simpler to understand:
- CCGT is the most efficient form of electricity generation (average efficiency = 46.6%), followed by nuclear (37.8%) and then coal (36%).
- The thermal efficiency of nuclear has been rising.
- There is absolutely no evidence from these numbers that the efficiency of large coal and CCGT plant is being impaired through cycling to balance the increasing load from wind and solar.
This post has grown to be substantially larger than I initially planned, and I have not yet got to the key point which is the fall in electricity demand since 2003 (Figure 2). Since electricity and energy consumption are correlated with gross domestic product (GDP) and national well being, a fall in electricity demand is a real cause for concern. Falling energy consumption may provide solace to environmentalists but since this is caused by energy scarcity and high price, the result is energy poverty for millions and a faltering economy that threatens government services (health, education, pensions) that most are dependent upon. Electricity consumption and GDP is next on the menu.