Insights: Low CO2 fuel sources powered 2019

Nearly half of all the electricity generated in Great Britain in 2019 was generated by low CO2 generation. In this Elexon Insight, our Market Advisor Emma Tribe uses electricity generation data to show how 2019 was powered demonstrate how the electricity market is on the road to Net Zero.

Generation Split

The pie chart below shows that 49.83% of electricity generation in 2019 was from low CO2 fuels. The second most dominant fuel was fossil fuels which represented 41.32%.

2019 electricity generation proportions

The generation volumes from the different fuel types have been grouped into emissions type as follows:

Fossil Fuel:

  • Gas
  • Coal

Low CO2 fuel:

  • Nuclear
  • Wind (embedded and transmission connected)
  • Biomass
  • Solar (embedded)
  • Hydro


  • Imports over interconnectors
  • Other fuel types

The fuel sources used in the county of origin for imported energy is unknown so imports from interconnectors have been grouped with other fuel types.

Total volume of electricity generated

The graph below gives the total volume of energy generation in terawatt hours (TWh) over the year for each of the emissions types. There was 145.11TWh generated by low CO2 sources in 2019, the majority of this generation came from wind (58.33TWh) and nuclear (52.71TWh).

Of the 120.33TWh generated by fossil fuels, 114.4TWh was generated by gas and the rest by coal.

2019 electricity generation by emissions type

Use the drill down and hierarchy arrows in the top left and right corners of the graph to view the volumes of generation from the different fuel types that make up each emissions group.

Gas generated more electricity than the combined generation of the next two highest generating fuel types, wind and nuclear. While more electricity was generated overall from low CO2 fuels, Great Britain is still heavily reliant on gas fueled generation as a major part of the fuel mix.

The monthly volume of electricity generated by each type of fuel is shown below. January saw the highest output from fossil fuels (15.09TWh) and was the only month where more energy was generated from fossil fuels than low CO2 sources.

December had the highest volume of energy generated by low CO2 sources in a month (14.69TWh). It also had the day with the highest generation from low CO2 fuels 0.61TWh on 8 December. In December gas generated 8.74MWh (32.61% of total generation) wind generated 6.91TWh (25.79%) and nuclear 4.88TWh (18.22%). Which was the highest volumes of wind and nuclear generated in a month in 2019.

January and December had the highest total volumes of generation, 28.78TWh and 26.80TWh respectively, as there is higher demand for electricity in these two colder months.

Monthly electricity generation trends

Low CO2 fuels generated more than 50% of electricity in six months: March, April, August, September, October and December.

Generation output at different times of day

The time of day when electricity is generated is also important. The half hour with the greatest total generation over the entire year was 7.10TWh between 17:30 and 18:00, this is the time with the greatest demand for electricity. The graph below shows the volume of energy generated by each type of fuel in each Settlement Period over the year.

Between 17:00 and 21:30 there was more electricity generated by fossil fuels than by low CO2 fuels. This is because there is less sunlight to fuel solar panels, but still high demand for energy. For the rest of the time more electricity was generated by low CO2 fuels.

Generation over a day

The time of year changes the profile of demand for electricity over a day. You can use the filters on the right hand side to filter for month.

Fossil fuel and low carbon generation use during the day

The graph below compares the percentage of the time of the day that fossil fuels and low CO­2 fuels are the dominant form of generation.

 For most of 2019, there was more low CO2 generation on the system than fossil fuel generation. Particularly overnight between 23:30 and 6:00 when low CO2 generation exceeded fossil fuel generation for more than 70% of the year. Overnight there is also less demand for energy so less generation is required.

Percentage of time as dominant fuel over a day

The times when the split between fossil fuels or low CO2 fuels being the greatest generator was closer to 50% is during the morning and evening peaks. This is also the time of day when flexible generation is required to ramp up and down to meet the demand peaks.

How 2019 compares to other years

The graph below shows the proportion of the fuel mix by emission type for the past 10 years.

2010’s electricity generation proportions

Looking at the fuel mix percentage over the last  decade, there is a clear trend of  decreasing generation from fossil fuels, and an  increase in generation from low CO2 fuels. In both 2018 and 2019, there was a higher proportion of generation from low CO2 fuels than from fossil fuels.

The contribution of fossil fuels to the GB fuel mix has reduced from 76.27% in 2010 to 41.32% in 2019. This decrease is due to a reduction in generation from 259.92TWh in 2010 to 120.33TWh, which is a 53.7% decrease. Over the same period generation from low CO2 has increased from 73.83TWh in 2010 to 145.11TWh in 2019.

Until November 2017 Biomass was considered an ‘other’ type fuel. The growth of generation from this low CO2 fuel has meant that Elexon changed how we reported the electricity generation fuel mix to industry. This combined with increases in wind generation resulted in low CO2 generation overtaking output from fossil fuels, in 2018 as shown in the graph.

Road to net zero

The commitments made by the government and the trends in fuel mix show that the electricity sector is on the road to net zero.

The times of the day and year when low CO2 fuel is available and generating is as important to achieving net zero as the total volume generated. Low CO2 flexible generation, or flexible demand will be needed for Great Britain to achieve a net zero electricity system. Elexon is supporting industry in achieving this goal.

This includes work to:

  • Allow customers to be served by multiple suppliers through the same meter
  • Proposing flexibility exchanges to trade demand side response and spare network capacity
  • Design metering arrangements which fully account for services provided by smaller generators, batteries behind the meter

Explore the data further

The data published by Elexon doesn’t include generation from embedded solar and wind generation, this data can be found on National Grid ESO’s Data Explorer.


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