In September 2024, Britain's electricity averaged 122 gCO₂/kWh, in the low band (70–139 g). That is 45% dirtier than August 2024 (84 g), and 23% cleaner than September 2023 (158 g). Wind made 27.5% of the electricity generated, gas 26.2%, nuclear 17.6% and imports 12.9%; low-carbon sources together made 60.7%. The cleanest half hour was 36 g at 13:30 on Saturday 14 September, and the dirtiest 242 g at 21:30 on Tuesday 3 September. Friday 27 September was both the cleanest day (64 g on average) and the windiest (53.2% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Sun 1 Sep | 83 | 68.7% | 34.7% | 5.4% | 17.0% | 48 |
| Mon 2 Sep | 171 | 49.9% | 17.1% | 2.5% | 36.7% | 48 |
| Tue 3 Sep | 188 | 48.6% | 13.7% | 5.4% | 39.5% | 48 |
| Wed 4 Sep | 198 | 44.2% | 8.1% | 5.5% | 43.9% | 48 |
| Thu 5 Sep | 76 | 69.9% | 38.7% | 1.6% | 14.5% | 48 |
| Fri 6 Sep | 113 | 61.9% | 27.4% | 5.0% | 24.2% | 48 |
| Sat 7 Sep | 155 | 46.9% | 9.4% | 3.2% | 34.8% | 48 |
| Sun 8 Sep | 101 | 60.4% | 22.3% | 4.0% | 20.4% | 48 |
| Mon 9 Sep | 82 | 70.6% | 37.8% | 4.9% | 18.0% | 48 |
| Tue 10 Sep | 69 | 78.1% | 51.8% | 3.6% | 15.3% | 48 |
| Wed 11 Sep | 68 | 76.2% | 46.5% | 6.7% | 14.7% | 48 |
| Thu 12 Sep | 112 | 65.2% | 30.1% | 6.9% | 24.0% | 48 |
| Fri 13 Sep | 131 | 58.6% | 18.9% | 8.3% | 26.8% | 48 |
| Sat 14 Sep | 75 | 72.2% | 38.0% | 8.4% | 17.2% | 48 |
| Sun 15 Sep | 97 | 65.0% | 31.1% | 5.4% | 21.1% | 48 |
| Mon 16 Sep | 153 | 52.1% | 12.5% | 8.2% | 34.2% | 48 |
| Tue 17 Sep | 136 | 56.9% | 16.1% | 9.0% | 27.7% | 48 |
| Wed 18 Sep | 129 | 59.9% | 21.3% | 7.5% | 25.6% | 48 |
| Thu 19 Sep | 147 | 53.8% | 17.0% | 6.8% | 32.0% | 48 |
| Fri 20 Sep | 119 | 59.9% | 26.4% | 4.4% | 25.2% | 48 |
| Sat 21 Sep | 122 | 58.5% | 23.6% | 5.2% | 25.6% | 48 |
| Sun 22 Sep | 154 | 51.1% | 18.7% | 2.0% | 34.3% | 48 |
| Mon 23 Sep | 180 | 47.6% | 17.8% | 1.8% | 41.8% | 48 |
| Tue 24 Sep | 145 | 57.3% | 25.2% | 3.1% | 31.5% | 48 |
| Wed 25 Sep | 171 | 50.2% | 19.2% | 3.2% | 39.1% | 48 |
| Thu 26 Sep | 95 | 68.3% | 41.2% | 3.7% | 20.5% | 48 |
| Fri 27 Sep | 64 | 77.7% | 53.2% | 4.6% | 13.8% | 48 |
| Sat 28 Sep | 135 | 55.2% | 23.7% | 6.9% | 28.4% | 48 |
| Sun 29 Sep | 90 | 66.4% | 38.0% | 3.2% | 17.6% | 48 |
| Mon 30 Sep | 95 | 70.0% | 46.7% | 1.5% | 19.6% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in September 2024, with September 2023 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, 17%
- Low (70–139 g): 348 hours, 48%
- Moderate (140–219 g): 237 hours, 33%
- High (220–299 g): 14 hours, 2%
Records in September 2024
- Cleanest half hour
- 36 g 13:30 on Saturday 14 September
- Dirtiest half hour
- 242 g 21:30 on Tuesday 3 September
- Most wind
- 68.2% 00:30 on Monday 30 September
- Most solar
- 30.1% 13:00 on Tuesday 17 September
- Most low-carbon
- 89.2% 04:00 on Friday 27 September
- Least gas
- 5.5% 12:00 on Sunday 1 September
- Cleanest day
- 64 g Friday 27 September
- Dirtiest day
- 198 g Wednesday 4 September
- Windiest day
- 53.2% wind Friday 27 September
- Sunniest day
- 9.0% solar Tuesday 17 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 21 October 2026.