In September 2026, Britain's electricity averaged 109 gCO₂/kWh, in the low band (70–139 g). That is 13% cleaner than August 2026 (125 g), and 3% cleaner than September 2025 (112 g). Wind made 38.0% of the electricity generated, gas 21.2%, nuclear 13.1% and biomass 8.6%; low-carbon sources together made 68.4%. The cleanest half hour was 27 g at 14:00 on Saturday 12 September, and the dirtiest 235 g at 18:00 on Monday 28 September. Saturday 19 September was both the cleanest day (60 g on average) and the windiest (63.1% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Tue 1 Sep | 110 | 74.4% | 39.9% | 9.3% | 20.1% | 48 |
| Wed 2 Sep | 145 | 69.0% | 34.6% | 5.6% | 24.3% | 48 |
| Thu 3 Sep | 73 | 79.5% | 47.0% | 6.9% | 11.1% | 48 |
| Fri 4 Sep | 71 | 81.5% | 51.3% | 6.1% | 13.2% | 48 |
| Sat 5 Sep | 82 | 83.2% | 45.6% | 10.8% | 16.3% | 48 |
| Sun 6 Sep | 77 | 80.1% | 42.5% | 9.7% | 14.4% | 48 |
| Mon 7 Sep | 83 | 76.6% | 46.8% | 7.2% | 12.9% | 48 |
| Tue 8 Sep | 84 | 79.8% | 54.2% | 6.8% | 14.7% | 48 |
| Wed 9 Sep | 107 | 64.1% | 32.6% | 7.5% | 20.8% | 48 |
| Thu 10 Sep | 113 | 63.9% | 35.8% | 6.6% | 23.0% | 48 |
| Fri 11 Sep | 129 | 59.3% | 26.4% | 7.6% | 26.3% | 48 |
| Sat 12 Sep | 81 | 74.3% | 45.4% | 6.2% | 15.0% | 48 |
| Sun 13 Sep | 164 | 43.9% | 10.2% | 5.6% | 34.1% | 48 |
| Mon 14 Sep | 151 | 55.7% | 28.0% | 5.9% | 33.2% | 48 |
| Tue 15 Sep | 78 | 75.0% | 46.8% | 7.2% | 14.5% | 48 |
| Wed 16 Sep | 112 | 64.0% | 33.1% | 6.2% | 22.0% | 48 |
| Thu 17 Sep | 66 | 81.3% | 55.3% | 6.1% | 12.2% | 48 |
| Fri 18 Sep | 61 | 82.0% | 58.2% | 6.0% | 11.7% | 48 |
| Sat 19 Sep | 60 | 83.6% | 63.1% | 5.5% | 12.9% | 48 |
| Sun 20 Sep | 81 | 75.4% | 48.6% | 9.2% | 15.4% | 48 |
| Mon 21 Sep | 162 | 49.6% | 16.1% | 8.3% | 31.1% | 48 |
| Tue 22 Sep | 190 | 44.1% | 12.1% | 7.2% | 40.8% | 48 |
| Wed 23 Sep | 130 | 61.0% | 30.0% | 6.4% | 25.7% | 48 |
| Thu 24 Sep | 134 | 59.7% | 25.6% | 8.5% | 25.4% | 48 |
| Fri 25 Sep | 142 | 57.8% | 26.1% | 6.8% | 29.1% | 48 |
| Sat 26 Sep | 112 | 65.3% | 29.7% | 9.4% | 21.7% | 48 |
| Sun 27 Sep | 83 | 75.0% | 45.5% | 4.4% | 15.0% | 48 |
| Mon 28 Sep | 180 | 51.8% | 18.9% | 7.4% | 36.3% | 48 |
| Tue 29 Sep | 101 | 70.6% | 44.1% | 5.1% | 19.8% | 48 |
| Wed 30 Sep | 105 | 71.6% | 47.4% | 6.0% | 21.5% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in September 2026, with September 2025 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Very low (under 70 g): 203 hours, 28%
- Low (70–139 g): 309 hours, 43%
- Moderate (140–219 g): 202 hours, 28%
- High (220–299 g): 7 hours, 1%
Records in September 2026
- Cleanest half hour
- 27 g 14:00 on Saturday 12 September
- Dirtiest half hour
- 235 g 18:00 on Monday 28 September
- Most wind
- 72.8% 04:30 on Saturday 19 September
- Most solar
- 32.8% 13:30 on Saturday 26 September
- Most low-carbon
- 95.3% 09:30 on Saturday 5 September
- Least gas
- 2.2% 13:00 on Thursday 3 September
- Cleanest day
- 60 g Saturday 19 September
- Dirtiest day
- 190 g Tuesday 22 September
- Windiest day
- 63.1% wind Saturday 19 September
- Sunniest day
- 10.8% solar Saturday 5 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 17 October 2026.