In October 2021, Britain's electricity averaged 150 gCO₂/kWh, in the moderate band (140–219 g). That is 27% cleaner than September 2021 (205 g), and 6% cleaner than October 2020 (160 g). Wind made 33.0% of the electricity generated, gas 31.0%, nuclear 15.1% and imports 8.9%; low-carbon sources together made 59.7%. The cleanest half hour was 46 g at 06:00 on Sunday 31 October, and the dirtiest 289 g at 20:30 on Friday 15 October. The cleanest day was Sunday 31 October (76 g on average); the windiest was Sunday 3 October (48.4% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Fri 1 Oct | 93 | 75.4% | 45.6% | 4.0% | 19.1% | 48 |
| Sat 2 Oct | 125 | 66.9% | 41.1% | 1.0% | 27.1% | 48 |
| Sun 3 Oct | 84 | 78.0% | 48.4% | 4.1% | 17.2% | 48 |
| Mon 4 Oct | 153 | 61.6% | 33.6% | 3.3% | 32.6% | 48 |
| Tue 5 Oct | 123 | 67.5% | 42.9% | 2.7% | 25.2% | 48 |
| Wed 6 Oct | 171 | 58.0% | 31.2% | 4.1% | 34.9% | 48 |
| Thu 7 Oct | 193 | 53.3% | 28.8% | 1.8% | 38.6% | 48 |
| Fri 8 Oct | 223 | 42.5% | 17.8% | 1.7% | 46.7% | 48 |
| Sat 9 Oct | 216 | 41.0% | 14.4% | 3.3% | 45.5% | 48 |
| Sun 10 Oct | 174 | 50.5% | 22.1% | 3.9% | 36.8% | 48 |
| Mon 11 Oct | 193 | 47.8% | 21.8% | 3.5% | 40.8% | 48 |
| Tue 12 Oct | 214 | 44.4% | 19.8% | 2.2% | 43.1% | 48 |
| Wed 13 Oct | 212 | 43.2% | 18.6% | 2.2% | 45.5% | 48 |
| Thu 14 Oct | 146 | 59.5% | 35.4% | 2.2% | 30.0% | 48 |
| Fri 15 Oct | 222 | 44.1% | 18.5% | 2.7% | 43.9% | 48 |
| Sat 16 Oct | 240 | 36.3% | 10.3% | 2.3% | 50.3% | 48 |
| Sun 17 Oct | 167 | 53.8% | 26.0% | 2.0% | 33.0% | 48 |
| Mon 18 Oct | 158 | 55.8% | 31.1% | 0.6% | 33.3% | 48 |
| Tue 19 Oct | 119 | 65.0% | 39.7% | 0.9% | 23.7% | 48 |
| Wed 20 Oct | 123 | 65.6% | 38.9% | 2.4% | 26.1% | 48 |
| Thu 21 Oct | 99 | 73.0% | 48.2% | 1.8% | 19.4% | 48 |
| Fri 22 Oct | 160 | 57.6% | 32.7% | 2.2% | 34.9% | 48 |
| Sat 23 Oct | 151 | 57.2% | 30.9% | 1.2% | 32.9% | 48 |
| Sun 24 Oct | 88 | 76.1% | 48.4% | 2.0% | 15.6% | 48 |
| Mon 25 Oct | 152 | 61.6% | 33.8% | 2.8% | 31.0% | 48 |
| Tue 26 Oct | 129 | 65.2% | 39.1% | 1.1% | 26.0% | 48 |
| Wed 27 Oct | 105 | 72.9% | 47.1% | 1.0% | 22.4% | 48 |
| Thu 28 Oct | 127 | 65.6% | 37.8% | 1.0% | 24.9% | 48 |
| Fri 29 Oct | 128 | 63.3% | 36.3% | 1.7% | 25.9% | 48 |
| Sat 30 Oct | 105 | 68.4% | 37.5% | 2.5% | 21.3% | 48 |
| Sun 31 Oct | 76 | 78.0% | 46.2% | 1.8% | 14.6% | 50 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in October 2021, with October 2020 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Very low (under 70 g): 58 hours, 8%
- Low (70–139 g): 281 hours, 38%
- Moderate (140–219 g): 287 hours, 38%
- High (220–299 g): 120 hours, 16%
Records in October 2021
- Cleanest half hour
- 46 g 06:00 on Sunday 31 October
- Dirtiest half hour
- 289 g 20:30 on Friday 15 October
- Most wind
- 59.8% 05:00 on Thursday 21 October
- Most solar
- 16.1% 11:30 on Sunday 3 October
- Most low-carbon
- 89.5% 07:00 on Sunday 31 October
- Least gas
- 8.9% 07:00 on Sunday 31 October
- Cleanest day
- 76 g Sunday 31 October
- Dirtiest day
- 240 g Saturday 16 October
- Windiest day
- 48.4% wind Sunday 3 October
- Sunniest day
- 4.1% solar Sunday 3 October
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.