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What happened to supply and demand in 2018?

GB electricity supply and demand in 2018.

Contribution made by all fuel sources

The data here are from the Elexon website, which includes data from all fuel sources, except solar. It gives separate data from Combined Cycle Gas Turbines (CCGT), Open Cycle Gas Turbines (OCGT), Oil, Coal, Nuclear, Wind, Pumped Storage, Hydro (non-pumped storage), Biomass, Other, French Interconnector, Irish Interconnector, Dutch Interconnector, East-West (Irish) Interconnector and, recently, the Belgium Interconnector (NEMO).

This graph shows the contribution to grid demand throughout November 2018 as an example:


Generation by fuel type Nov 2018

The picture is clearer if only the five power sources being analysed are plotted:


Generation by fuel type Feb 2018

From this it can be seen that nuclear provided a reasonably steady base load at around 7500MW and biomass at about 800MW. CCGT (hereafter referred to as gas) and coal were being cycled to match demand. Wind was also cycling, but this was an uncontrollable cycle with low wind often being at times of high demand and vice-versa.

The graph clearly shows that, in the absence of coal, gas was the only power source which had the flexibility and controllability to provide the power required as demand on the grid increased and decreased over each day. It can also be seen that although coal was mainly used in the winter months it was still making a significant contribution.

Average contribution made by renewables and fossil fuels to demand

The Elexon data has been analysed to determine the average contributions to grid demand from nuclear, wind, biomass, gas and coal as shown in this table:

Average Contribution to Grid Demand (%) 2018
 NuclearWindBiomassGasCoal
January19.116.93.244.35.5
February20.114.33.741.110.8
March19.913.84.638.614.6
April23.013.75.844.72.2
May24.810.87.444.11.2
June27.18.76.246.20.9
July25.86.86.249.10.7
August27.511.67.041.31.5
September25.817.67.133.36.3
October18.717.67.442.34.2
November17.919.56.538.29.2
December19.217.56.541.25.5
Average22.114.35.941.95.6

The nuclear contribution provided a base load and therefore contributed a higher percentage in summer when demand was at its lowest. Even at an average, the contribution of wind varied by a factor of 3. Gas gave a steady average, with contribution being reduced at times of high wind or high coal input to the grid. Coal was little used in summer but was used to supplement gas in winter months.

However, these averages mask what was really happening. What was critical was how the various fuel sources could be controlled and how they contributed when demand peaked.

Minimum monthly contributions

The next table shows the minimum contributions from nuclear, wind, biomass, gas and coal each month. As demand fluctuates month by month and hour by hour, the data is presented in terms of percentage contribution:

Minimum Contribution (%) 2018
 NuclearWindBiomassGasCoal
January12.30.61.314.10.0
February14.00.92.69.30.0
March12.60.82.67.30.9
April16.10.52.516.40.0
May12.60.52.615.90.9
June18.00.24.917.40.0
July19.40.31.819.60.0
August19.50.23.111.20.0
September17.22.82.913.50.0
October12.22.53.915.90.0
November12.72.13.012.31.0
December12.91.83.814.10.0

Important points to note:

  • Nuclear’s base load contribution showed a higher percentage in summer months when demand was lower and vice versa.

  • Wind provided little contribution every month at times when there was little wind blowing.

  • Biomass became a steady contributor as the year progressed.

  • Gas contribution was reduced at times of low demand and when there was a high wind contribution, but still provided the most significant contribution overall.

  • Coal was often zero at times of low demand, and the output from coal fired stations was brought on only at times of high demand.

Minimum contributions at times of peak demand

The table above, and the graphs, clearly show that nuclear provided a steady base contribution, wind had no correlation to demand, biomass was providing an increasing - if still low level - base support, gas was the critical power source being used to meet grid demand and coal was used to support gas at times of highest demand.

To examine this in more detail, the minimum contributions from nuclear, wind, biomass, gas and coal at times of peak demand during each day during 2018 have been extracted:

Minimum Contribution at peak demand (%) 2018
 NuclearWindBiomassGasCoal
January12.30.81.438.31.2
February14.01.42.626.14.0
March12.62.02.627.13.0
April16.60.63.635.80.0
May18.01.22.625.20.0
June19.40.82.732.40.0
July19.40.92.626.30.0
August20.00.33.324.90.0
September17.23.62.925.61.8
October12.23.43.931.70.0
November12.72.63.031.14.1
December12.91.94.035.93.3

It can be seen that although gas was being flexed to meet demand it still made the most significant contribution by far every month at times of peak demand. Nuclear was proving a steady contribution, being a higher percentage in summer when demand was lower. The contribution of biomass at times of peak demand increased through the year as capacity was increased. Coal often made no contribution at peak demand as it was only brought on stream when other power sources could not meet demand in the winter months.

The table shows there was a time in every month when wind could not be relied upon to make any significant contribution to peak demand.

We can now use the information above to answer some specific questions.

How did renewables contribute to demand on average through 2018?

From the Elexon website, the official source for power being fed into the grid, the contribution from nuclear in 2018 averaged 22.1% of demand, providing an input of between 17.9% and 27.5% in any month. This did not vary with demand and so provided a steady base supply.

Although wind contributed 14.3% on average, this varied widely from month to month, with 6.8% being the minimum and 19.5% the maximum. This variation was due to the strength of the wind and not to any variation in demand.

How did this compare with contributions from fossil fuelled power stations?

In 2018, gas was by far the biggest contributor to demand, supplying 41.9% on average with an input varying between 33.3% in summer and 49.1% in winter. (It should be noted that the lowest contribution was in September when the contribution from other fuel sources were particularly high.) Output from CCGT stations was of course being controlled to meet demand. Coal showed the largest variation in contribution from 0.7% in July to 14.6% in March, with an average of 5.6%. Coal was brought on stream at times of high demand in winter, to meet peak demand or when the price of gas was higher.

How was peak demand met?

It is clear from the graphs and tables above, that whilst nuclear and biomass provided a steady base supply, the fuels being used to meet peak demand were gas and, to a lesser extent, coal. Wind cannot be relied upon to provide power at times of peak demand as output is intermittent and unpredictable.

In the absence of coal, CCGT Gas is the only fuel source which can be controlled to meet the ever fluctuating demand on the grid. Therefore, if there is to be any technology in the power supply field in GB designated as key then it must be gas.

Can renewables meet demand in the future or will GB have to continue to rely on fossil fuels?

The answer to this question is that it depends on the renewable power source. Nuclear and - to a lesser extent - biomass are providing a steady base contribution. But the only fuel sources which can be relied on to be flexible to meet demand are gas and coal.

Wind turbines may contribute to reducing the need for gas, and hence reduce carbon emissions, when the wind blows but are totally unreliable in producing power as and when required by fluctuating demand.