In September 2023, Britain's electricity averaged 158 gCO₂/kWh, in the moderate band (140–219 g). That is 2% cleaner than August 2023 (161 g), and 25% cleaner than September 2022 (210 g). Gas made 34.3% of the electricity generated, wind 25.6%, nuclear 18.6% and imports 9.1%; low-carbon sources together made 55.3%. The cleanest half hour was 29 g at 14:30 on Monday 18 September, and the dirtiest 280 g at 06:00 on Friday 8 September. Sunday 24 September was both the cleanest day (59 g on average) and the windiest (58.2% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Fri 1 Sep | 219 | 38.3% | 8.8% | 4.5% | 53.0% | 48 |
| Sat 2 Sep | 189 | 43.9% | 9.2% | 7.1% | 44.5% | 48 |
| Sun 3 Sep | 126 | 58.6% | 20.9% | 8.8% | 25.2% | 48 |
| Mon 4 Sep | 170 | 49.1% | 15.9% | 8.1% | 37.7% | 48 |
| Tue 5 Sep | 194 | 47.1% | 16.4% | 7.8% | 44.9% | 48 |
| Wed 6 Sep | 218 | 41.1% | 11.4% | 6.7% | 51.1% | 48 |
| Thu 7 Sep | 229 | 36.6% | 6.7% | 6.3% | 52.8% | 48 |
| Fri 8 Sep | 252 | 32.2% | 2.3% | 6.0% | 56.6% | 48 |
| Sat 9 Sep | 203 | 41.3% | 8.2% | 7.6% | 46.5% | 48 |
| Sun 10 Sep | 213 | 38.8% | 8.1% | 4.8% | 48.5% | 48 |
| Mon 11 Sep | 214 | 44.1% | 17.0% | 4.2% | 48.0% | 48 |
| Tue 12 Sep | 236 | 40.1% | 13.9% | 3.1% | 52.5% | 48 |
| Wed 13 Sep | 182 | 52.3% | 22.2% | 6.1% | 39.9% | 48 |
| Thu 14 Sep | 184 | 52.1% | 23.5% | 5.0% | 38.8% | 48 |
| Fri 15 Sep | 198 | 42.4% | 11.4% | 5.9% | 44.7% | 48 |
| Sat 16 Sep | 143 | 53.8% | 22.2% | 4.3% | 30.4% | 48 |
| Sun 17 Sep | 127 | 58.8% | 29.9% | 2.5% | 25.3% | 48 |
| Mon 18 Sep | 69 | 75.6% | 46.9% | 4.3% | 14.9% | 48 |
| Tue 19 Sep | 61 | 79.7% | 55.4% | 1.9% | 11.8% | 48 |
| Wed 20 Sep | 71 | 76.3% | 53.5% | 2.1% | 13.6% | 48 |
| Thu 21 Sep | 145 | 58.2% | 27.3% | 5.3% | 32.0% | 48 |
| Fri 22 Sep | 134 | 58.2% | 24.3% | 5.5% | 28.0% | 48 |
| Sat 23 Sep | 139 | 58.8% | 24.0% | 6.8% | 25.6% | 48 |
| Sun 24 Sep | 59 | 82.2% | 58.2% | 2.9% | 12.2% | 48 |
| Mon 25 Sep | 114 | 72.3% | 43.1% | 6.1% | 20.7% | 48 |
| Tue 26 Sep | 145 | 66.7% | 38.7% | 4.3% | 25.9% | 48 |
| Wed 27 Sep | 143 | 62.5% | 36.9% | 2.0% | 28.7% | 48 |
| Thu 28 Sep | 105 | 73.2% | 48.8% | 2.3% | 21.2% | 48 |
| Fri 29 Sep | 104 | 72.0% | 42.1% | 6.0% | 21.2% | 48 |
| Sat 30 Sep | 164 | 52.9% | 22.2% | 3.6% | 33.1% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in September 2023, with September 2022 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Very low (under 70 g): 96 hours, 13%
- Low (70–139 g): 182 hours, 25%
- Moderate (140–219 g): 313 hours, 43%
- High (220–299 g): 130 hours, 18%
Records in September 2023
- Cleanest half hour
- 29 g 14:30 on Monday 18 September
- Dirtiest half hour
- 280 g 06:00 on Friday 8 September
- Most wind
- 64.3% 01:00 on Thursday 28 September
- Most solar
- 27.7% 12:30 on Sunday 3 September
- Most low-carbon
- 87.9% 02:00 on Thursday 28 September
- Least gas
- 5.2% 14:00 on Monday 18 September
- Cleanest day
- 59 g Sunday 24 September
- Dirtiest day
- 252 g Friday 8 September
- Windiest day
- 58.2% wind Sunday 24 September
- Sunniest day
- 8.8% solar Sunday 3 September
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 23 October 2026.