In December 2020, Britain's electricity averaged 185 gCO₂/kWh, in the moderate band (140–219 g). That is 5% dirtier than November 2020 (177 g), and 9% cleaner than December 2019 (203 g). Gas made 37.6% of the electricity generated, wind 22.7%, nuclear 19.7% and biomass 7.4%; low-carbon sources together made 53.2%. The cleanest half hour was 57 g at 02:00 on Thursday 24 December, and the dirtiest 307 g at 14:00 on Tuesday 22 December. Saturday 26 December was both the cleanest day (86 g on average) and the windiest (45.4% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Tue 1 Dec | 205 | 49.2% | 17.5% | 1.5% | 44.2% | 48 |
| Wed 2 Dec | 239 | 45.8% | 15.8% | 0.5% | 47.7% | 48 |
| Thu 3 Dec | 218 | 45.7% | 16.4% | 0.2% | 45.2% | 48 |
| Fri 4 Dec | 163 | 59.2% | 29.5% | 0.5% | 33.8% | 48 |
| Sat 5 Dec | 200 | 48.3% | 15.8% | 1.2% | 42.9% | 48 |
| Sun 6 Dec | 259 | 34.9% | 3.2% | 1.0% | 55.1% | 48 |
| Mon 7 Dec | 264 | 37.6% | 8.3% | 0.6% | 52.3% | 48 |
| Tue 8 Dec | 249 | 42.5% | 15.1% | 0.8% | 48.5% | 48 |
| Wed 9 Dec | 245 | 44.0% | 14.6% | 0.4% | 47.5% | 48 |
| Thu 10 Dec | 210 | 53.9% | 25.4% | 0.3% | 39.3% | 48 |
| Fri 11 Dec | 230 | 48.3% | 18.1% | 0.5% | 42.6% | 48 |
| Sat 12 Dec | 218 | 42.8% | 10.6% | 0.9% | 47.2% | 48 |
| Sun 13 Dec | 143 | 60.7% | 28.7% | 0.2% | 28.1% | 48 |
| Mon 14 Dec | 148 | 63.4% | 32.7% | 0.8% | 30.0% | 48 |
| Tue 15 Dec | 178 | 55.4% | 24.3% | 1.6% | 36.8% | 48 |
| Wed 16 Dec | 150 | 62.1% | 32.9% | 0.4% | 29.6% | 48 |
| Thu 17 Dec | 160 | 61.2% | 31.2% | 1.4% | 32.7% | 48 |
| Fri 18 Dec | 122 | 68.2% | 39.6% | 0.2% | 22.7% | 48 |
| Sat 19 Dec | 95 | 73.5% | 42.9% | 1.4% | 18.3% | 48 |
| Sun 20 Dec | 113 | 70.5% | 38.1% | 1.5% | 21.2% | 48 |
| Mon 21 Dec | 166 | 55.4% | 25.8% | 0.2% | 33.4% | 48 |
| Tue 22 Dec | 229 | 43.4% | 13.7% | 0.4% | 44.4% | 48 |
| Wed 23 Dec | 172 | 53.9% | 22.2% | 0.3% | 33.4% | 48 |
| Thu 24 Dec | 123 | 65.8% | 35.5% | 1.6% | 26.1% | 48 |
| Fri 25 Dec | 137 | 60.0% | 27.1% | 1.5% | 30.9% | 48 |
| Sat 26 Dec | 86 | 76.5% | 45.4% | 0.5% | 16.5% | 48 |
| Sun 27 Dec | 131 | 64.8% | 30.2% | 2.0% | 27.0% | 48 |
| Mon 28 Dec | 230 | 38.3% | 7.7% | 0.6% | 49.3% | 48 |
| Tue 29 Dec | 213 | 41.9% | 12.6% | 0.7% | 46.3% | 48 |
| Wed 30 Dec | 228 | 41.1% | 10.9% | 0.9% | 48.2% | 48 |
| Thu 31 Dec | 224 | 41.5% | 11.3% | 1.2% | 45.9% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in December 2020, with December 2019 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Very low (under 70 g): 21 hours, 3%
- Low (70–139 g): 185 hours, 25%
- Moderate (140–219 g): 284 hours, 38%
- High (220–299 g): 249 hours, 33%
- Very high (300 g or more): 7 hours, 1%
Records in December 2020
- Cleanest half hour
- 57 g 02:00 on Thursday 24 December
- Dirtiest half hour
- 307 g 14:00 on Tuesday 22 December
- Most wind
- 52.5% 23:30 on Saturday 19 December
- Most solar
- 12.0% 11:30 on Sunday 27 December
- Most low-carbon
- 85.4% 03:30 on Friday 18 December
- Least gas
- 0.0% 06:30 on Monday 21 December
- Cleanest day
- 86 g Saturday 26 December
- Dirtiest day
- 264 g Monday 7 December
- Windiest day
- 45.4% wind Saturday 26 December
- Sunniest day
- 2.0% solar Sunday 27 December
About these figures
GridMonkey records NESO's carbon intensity and generation mix for Great Britain every half hour: the actual figure where NESO has published one, otherwise its forecast. They are added up by UK calendar day and month. Percentages are shares of the electricity generated, imports included, so the fuels add up to 100%. Low-carbon means wind, solar, nuclear, biomass and hydro. The carbon bands are GridMonkey's: very low under 70 g, low 70–139 g, moderate 140–219 g, high 220–299 g and very high 300 g or more, per kWh. Northern Ireland has its own grid and isn't included.
To see the grid now, open GridMonkey. For the wind farms that ran hardest this week, see the wind farm league table.
Data: NESO Carbon Intensity API (carbonintensity.org.uk), licensed under CC BY 4.0, recorded and summarised by GridMonkey. Figures as of 28 October 2026.