In December 2021, Britain's electricity averaged 192 gCO₂/kWh, in the moderate band (140–219 g). That is 4% dirtier than November 2021 (184 g), and 4% dirtier than December 2020 (185 g). Gas made 36.6% of the electricity generated, wind 26.8%, nuclear 16.3% and imports 8.4%; low-carbon sources together made 53.0%. The cleanest half hour was 43 g at 03:30 on Thursday 30 December, and the dirtiest 316 g at 06:30 on Tuesday 21 December. Thursday 30 December was both the cleanest day (75 g on average) and the windiest (47.5% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Wed 1 Dec | 144 | 66.1% | 42.5% | 0.8% | 26.5% | 48 |
| Thu 2 Dec | 192 | 54.2% | 29.1% | 1.6% | 36.1% | 48 |
| Fri 3 Dec | 213 | 48.8% | 25.2% | 0.4% | 41.5% | 48 |
| Sat 4 Dec | 143 | 62.2% | 37.8% | 1.4% | 29.2% | 48 |
| Sun 5 Dec | 172 | 57.1% | 32.5% | 0.7% | 33.0% | 48 |
| Mon 6 Dec | 207 | 51.7% | 29.6% | 0.4% | 41.4% | 48 |
| Tue 7 Dec | 188 | 55.0% | 33.3% | 0.2% | 36.5% | 48 |
| Wed 8 Dec | 177 | 59.4% | 36.1% | 0.7% | 32.0% | 48 |
| Thu 9 Dec | 216 | 50.7% | 26.3% | 0.9% | 40.0% | 48 |
| Fri 10 Dec | 183 | 57.3% | 33.2% | 1.3% | 33.8% | 48 |
| Sat 11 Dec | 202 | 51.3% | 26.8% | 0.3% | 32.9% | 48 |
| Sun 12 Dec | 150 | 62.2% | 35.2% | 0.6% | 23.8% | 48 |
| Mon 13 Dec | 204 | 53.3% | 27.2% | 0.3% | 37.7% | 48 |
| Tue 14 Dec | 211 | 51.9% | 27.5% | 0.4% | 37.7% | 48 |
| Wed 15 Dec | 196 | 53.4% | 28.4% | 0.5% | 36.6% | 48 |
| Thu 16 Dec | 271 | 34.2% | 9.2% | 0.4% | 53.5% | 48 |
| Fri 17 Dec | 278 | 30.6% | 5.3% | 0.6% | 55.7% | 48 |
| Sat 18 Dec | 258 | 31.4% | 6.7% | 0.5% | 53.1% | 48 |
| Sun 19 Dec | 251 | 34.1% | 6.4% | 0.3% | 53.9% | 48 |
| Mon 20 Dec | 281 | 32.9% | 6.1% | 0.2% | 55.8% | 48 |
| Tue 21 Dec | 296 | 32.0% | 4.5% | 0.3% | 56.2% | 48 |
| Wed 22 Dec | 250 | 42.7% | 15.0% | 0.4% | 46.9% | 48 |
| Thu 23 Dec | 198 | 50.2% | 21.5% | 0.2% | 41.6% | 48 |
| Fri 24 Dec | 173 | 55.2% | 26.4% | 0.4% | 33.6% | 48 |
| Sat 25 Dec | 131 | 66.9% | 44.4% | 0.3% | 22.7% | 48 |
| Sun 26 Dec | 134 | 65.8% | 41.6% | 0.8% | 23.6% | 30 |
| Mon 27 Dec | 156 | 53.9% | 22.7% | 0.2% | 36.5% | 12 |
| Tue 28 Dec | 153 | 58.6% | 23.5% | 0.6% | 31.2% | 48 |
| Wed 29 Dec | 105 | 70.5% | 38.1% | 0.4% | 18.3% | 48 |
| Thu 30 Dec | 75 | 79.9% | 47.5% | 0.3% | 12.8% | 48 |
| Fri 31 Dec | 88 | 76.5% | 43.5% | 0.7% | 14.2% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in December 2021, with December 2020 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Very low (under 70 g): 22 hours, 3%
- Low (70–139 g): 172 hours, 24%
- Moderate (140–219 g): 239 hours, 33%
- High (220–299 g): 263 hours, 37%
- Very high (300 g or more): 22 hours, 3%
Records in December 2021
- Cleanest half hour
- 43 g 03:30 on Thursday 30 December
- Dirtiest half hour
- 316 g 06:30 on Tuesday 21 December
- Most wind
- 58.7% 02:30 on Wednesday 1 December
- Most solar
- 8.7% 11:30 on Thursday 2 December
- Most low-carbon
- 91.8% 03:30 on Thursday 30 December
- Least gas
- 6.2% 23:30 on Wednesday 29 December
- Cleanest day
- 75 g Thursday 30 December
- Dirtiest day
- 296 g Tuesday 21 December
- Windiest day
- 47.5% wind Thursday 30 December
- Sunniest day
- 1.6% solar Thursday 2 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 26 October 2026.