In December 2025, Britain's electricity averaged 120 gCO₂/kWh, in the low band (70–139 g). That is 6% cleaner than November 2025 (127 g), and 6% cleaner than December 2024 (128 g). Wind made 41.7% of the electricity generated, gas 26.3%, imports 11.8% and nuclear 11.4%; low-carbon sources together made 61.9%. The cleanest half hour was 38 g at 23:00 on Sunday 14 December, and the dirtiest 241 g at 07:00 on Tuesday 16 December. Sunday 14 December was both the cleanest day (63 g on average) and the windiest (63.9% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Mon 1 Dec | 108 | 67.4% | 47.4% | 0.3% | 21.3% | 48 |
| Tue 2 Dec | 135 | 59.9% | 39.0% | 2.4% | 31.4% | 48 |
| Wed 3 Dec | 176 | 50.1% | 29.3% | 2.3% | 43.1% | 48 |
| Thu 4 Dec | 146 | 58.2% | 38.8% | 0.6% | 33.7% | 48 |
| Fri 5 Dec | 143 | 59.6% | 41.1% | 1.1% | 34.0% | 48 |
| Sat 6 Dec | 83 | 69.7% | 50.0% | 1.1% | 14.8% | 48 |
| Sun 7 Dec | 98 | 65.0% | 42.5% | 0.4% | 16.6% | 48 |
| Mon 8 Dec | 78 | 72.4% | 51.7% | 1.0% | 14.5% | 48 |
| Tue 9 Dec | 69 | 76.9% | 59.6% | 0.3% | 13.4% | 48 |
| Wed 10 Dec | 73 | 78.5% | 60.0% | 2.0% | 15.2% | 48 |
| Thu 11 Dec | 105 | 68.9% | 50.4% | 1.5% | 24.0% | 48 |
| Fri 12 Dec | 170 | 49.4% | 28.8% | 1.2% | 41.1% | 48 |
| Sat 13 Dec | 100 | 67.4% | 44.7% | 2.5% | 22.1% | 48 |
| Sun 14 Dec | 63 | 80.3% | 63.9% | 1.7% | 13.9% | 48 |
| Mon 15 Dec | 140 | 56.4% | 37.9% | 0.6% | 33.3% | 48 |
| Tue 16 Dec | 197 | 40.8% | 20.8% | 1.1% | 48.1% | 48 |
| Wed 17 Dec | 138 | 60.7% | 43.7% | 0.4% | 32.4% | 48 |
| Thu 18 Dec | 90 | 69.1% | 53.1% | 0.2% | 17.7% | 48 |
| Fri 19 Dec | 103 | 69.7% | 50.1% | 2.4% | 22.6% | 48 |
| Sat 20 Dec | 127 | 57.5% | 36.3% | 2.0% | 29.4% | 48 |
| Sun 21 Dec | 125 | 57.0% | 36.6% | 0.5% | 26.6% | 48 |
| Mon 22 Dec | 130 | 56.2% | 37.9% | 1.1% | 28.6% | 48 |
| Tue 23 Dec | 116 | 59.2% | 41.3% | 0.2% | 23.2% | 48 |
| Wed 24 Dec | 94 | 65.7% | 45.7% | 2.3% | 17.2% | 48 |
| Thu 25 Dec | 71 | 73.3% | 53.3% | 2.9% | 13.4% | 48 |
| Fri 26 Dec | 113 | 62.2% | 38.1% | 2.3% | 24.7% | 48 |
| Sat 27 Dec | 100 | 63.2% | 41.3% | 2.0% | 20.0% | 48 |
| Sun 28 Dec | 178 | 41.6% | 18.1% | 0.5% | 39.7% | 48 |
| Mon 29 Dec | 179 | 45.9% | 23.4% | 0.6% | 40.6% | 48 |
| Tue 30 Dec | 161 | 50.4% | 26.2% | 1.8% | 35.0% | 48 |
| Wed 31 Dec | 116 | 65.0% | 41.3% | 2.6% | 23.3% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in December 2025, with December 2024 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Very low (under 70 g): 123 hours, 16%
- Low (70–139 g): 370 hours, 50%
- Moderate (140–219 g): 242 hours, 33%
- High (220–299 g): 10 hours, 1%
Records in December 2025
- Cleanest half hour
- 38 g 23:00 on Sunday 14 December
- Dirtiest half hour
- 241 g 07:00 on Tuesday 16 December
- Most wind
- 72.0% 04:30 on Wednesday 10 December
- Most solar
- 15.3% 12:00 on Thursday 25 December
- Most low-carbon
- 87.8% 04:30 on Wednesday 10 December
- Least gas
- 6.4% 20:00 on Sunday 7 December
- Cleanest day
- 63 g Sunday 14 December
- Dirtiest day
- 197 g Tuesday 16 December
- Windiest day
- 63.9% wind Sunday 14 December
- Sunniest day
- 2.9% solar Thursday 25 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 19 October 2026.