In December 2023, Britain's electricity averaged 123 gCO₂/kWh, in the low band (70–139 g). That is 24% cleaner than November 2023 (161 g), and 31% cleaner than December 2022 (179 g). Wind made 42.6% of the electricity generated, gas 25.4%, nuclear 14.9% and imports 7.0%; low-carbon sources together made 66.4%. The cleanest half hour was 26 g at 13:30 on Thursday 28 December, and the dirtiest 309 g at 05:30 on Saturday 2 December. The cleanest day was Thursday 28 December (39 g on average); the windiest was Sunday 24 December (62.7% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Fri 1 Dec | 284 | 30.1% | 6.3% | 1.6% | 61.9% | 48 |
| Sat 2 Dec | 278 | 27.8% | 6.0% | 1.1% | 60.7% | 48 |
| Sun 3 Dec | 207 | 44.6% | 20.8% | 0.4% | 41.3% | 48 |
| Mon 4 Dec | 177 | 56.9% | 34.9% | 0.2% | 35.5% | 48 |
| Tue 5 Dec | 215 | 47.1% | 24.5% | 0.6% | 44.9% | 48 |
| Wed 6 Dec | 244 | 42.5% | 19.2% | 1.5% | 53.4% | 48 |
| Thu 7 Dec | 151 | 66.7% | 46.3% | 0.1% | 29.8% | 48 |
| Fri 8 Dec | 156 | 64.0% | 40.0% | 1.1% | 30.5% | 48 |
| Sat 9 Dec | 62 | 78.3% | 56.6% | 0.7% | 10.4% | 48 |
| Sun 10 Dec | 96 | 69.5% | 47.1% | 0.5% | 16.8% | 48 |
| Mon 11 Dec | 177 | 52.0% | 28.9% | 1.2% | 36.7% | 48 |
| Tue 12 Dec | 194 | 48.9% | 25.8% | 0.6% | 41.5% | 48 |
| Wed 13 Dec | 192 | 52.0% | 27.4% | 0.6% | 41.2% | 48 |
| Thu 14 Dec | 201 | 51.6% | 28.1% | 0.7% | 44.7% | 48 |
| Fri 15 Dec | 153 | 62.7% | 39.7% | 0.5% | 34.3% | 48 |
| Sat 16 Dec | 71 | 77.6% | 55.4% | 0.9% | 14.7% | 48 |
| Sun 17 Dec | 63 | 81.2% | 58.2% | 0.9% | 12.2% | 48 |
| Mon 18 Dec | 107 | 71.1% | 47.1% | 0.3% | 22.1% | 48 |
| Tue 19 Dec | 113 | 69.0% | 45.4% | 0.4% | 24.3% | 48 |
| Wed 20 Dec | 52 | 82.6% | 59.2% | 0.6% | 9.9% | 48 |
| Thu 21 Dec | 47 | 83.5% | 60.2% | 0.7% | 9.3% | 48 |
| Fri 22 Dec | 51 | 80.2% | 57.6% | 0.6% | 11.0% | 48 |
| Sat 23 Dec | 46 | 85.9% | 61.4% | 1.0% | 9.6% | 48 |
| Sun 24 Dec | 44 | 86.3% | 62.7% | 0.5% | 8.2% | 48 |
| Mon 25 Dec | 56 | 80.5% | 53.4% | 0.4% | 10.3% | 48 |
| Tue 26 Dec | 101 | 66.2% | 34.2% | 1.5% | 21.8% | 48 |
| Wed 27 Dec | 46 | 85.1% | 58.6% | 0.1% | 8.8% | 48 |
| Thu 28 Dec | 39 | 84.8% | 62.2% | 0.8% | 7.8% | 48 |
| Fri 29 Dec | 53 | 80.0% | 53.9% | 1.0% | 10.2% | 48 |
| Sat 30 Dec | 53 | 77.2% | 52.4% | 0.4% | 10.0% | 48 |
| Sun 31 Dec | 71 | 72.7% | 47.5% | 1.0% | 14.7% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in December 2023, with December 2022 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Very low (under 70 g): 321 hours, 43%
- Low (70–139 g): 149 hours, 20%
- Moderate (140–219 g): 143 hours, 19%
- High (220–299 g): 127 hours, 17%
- Very high (300 g or more): 6 hours, 1%
Records in December 2023
- Cleanest half hour
- 26 g 13:30 on Thursday 28 December
- Dirtiest half hour
- 309 g 05:30 on Saturday 2 December
- Most wind
- 69.2% 02:30 on Thursday 21 December
- Most solar
- 8.0% 12:00 on Friday 1 December
- Most low-carbon
- 90.5% 03:00 on Sunday 24 December
- Least gas
- 4.5% 11:00 on Thursday 28 December
- Cleanest day
- 39 g Thursday 28 December
- Dirtiest day
- 284 g Friday 1 December
- Windiest day
- 62.7% wind Sunday 24 December
- Sunniest day
- 1.6% solar Friday 1 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 22 October 2026.