In September 2020, Britain's electricity averaged 195 gCO₂/kWh, in the moderate band (140–219 g). That is 3% cleaner than August 2020 (202 g), and 10% dirtier than September 2019 (178 g). Gas made 43.4% of the electricity generated, wind 21.8%, nuclear 17.4% and biomass 5.2%; low-carbon sources together made 50.9%. The cleanest half hour was 63 g at 12:00 on Sunday 13 September, and the dirtiest 332 g at 21:30 on Tuesday 15 September. The cleanest day was Saturday 12 September (102 g on average); the windiest was Saturday 26 September (42.3% 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 | 271 | 34.2% | 8.4% | 6.3% | 60.3% | 48 |
| Wed 2 Sep | 198 | 49.9% | 25.9% | 3.9% | 47.2% | 48 |
| Thu 3 Sep | 157 | 58.5% | 37.6% | 3.3% | 35.2% | 48 |
| Fri 4 Sep | 155 | 59.4% | 34.8% | 4.2% | 34.3% | 48 |
| Sat 5 Sep | 139 | 61.9% | 33.3% | 6.8% | 30.2% | 48 |
| Sun 6 Sep | 239 | 34.6% | 7.2% | 5.5% | 52.0% | 48 |
| Mon 7 Sep | 207 | 47.4% | 24.6% | 3.1% | 45.0% | 48 |
| Tue 8 Sep | 200 | 49.7% | 24.8% | 4.3% | 44.4% | 48 |
| Wed 9 Sep | 191 | 52.8% | 25.7% | 5.0% | 44.5% | 48 |
| Thu 10 Sep | 249 | 38.2% | 9.6% | 4.8% | 60.1% | 48 |
| Fri 11 Sep | 180 | 55.0% | 26.5% | 3.7% | 42.4% | 48 |
| Sat 12 Sep | 102 | 73.3% | 37.2% | 7.6% | 21.9% | 48 |
| Sun 13 Sep | 105 | 71.8% | 36.2% | 8.0% | 21.9% | 48 |
| Mon 14 Sep | 240 | 42.6% | 9.4% | 6.5% | 51.7% | 48 |
| Tue 15 Sep | 299 | 32.7% | 3.2% | 4.9% | 60.5% | 48 |
| Wed 16 Sep | 242 | 41.0% | 13.0% | 4.4% | 56.1% | 48 |
| Thu 17 Sep | 214 | 46.5% | 15.8% | 6.5% | 50.8% | 48 |
| Fri 18 Sep | 181 | 54.6% | 21.7% | 6.6% | 42.4% | 48 |
| Sat 19 Sep | 124 | 65.6% | 29.4% | 7.0% | 25.7% | 48 |
| Sun 20 Sep | 172 | 52.9% | 16.4% | 6.3% | 37.3% | 48 |
| Mon 21 Sep | 258 | 39.4% | 7.8% | 5.6% | 56.7% | 48 |
| Tue 22 Sep | 204 | 49.8% | 20.7% | 4.1% | 48.9% | 48 |
| Wed 23 Sep | 233 | 43.3% | 16.5% | 2.1% | 54.7% | 48 |
| Thu 24 Sep | 199 | 46.7% | 18.0% | 3.8% | 43.7% | 48 |
| Fri 25 Sep | 134 | 67.1% | 35.2% | 5.0% | 26.1% | 48 |
| Sat 26 Sep | 106 | 71.5% | 42.3% | 4.6% | 22.3% | 48 |
| Sun 27 Sep | 146 | 60.0% | 25.5% | 4.9% | 31.5% | 48 |
| Mon 28 Sep | 235 | 43.0% | 14.4% | 3.1% | 51.6% | 48 |
| Tue 29 Sep | 270 | 32.6% | 6.8% | 3.6% | 58.2% | 48 |
| Wed 30 Sep | 184 | 52.5% | 26.1% | 1.3% | 43.2% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in September 2020, with September 2019 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Very low (under 70 g): 2 hours, 0%
- Low (70–139 g): 152 hours, 21%
- Moderate (140–219 g): 301 hours, 42%
- High (220–299 g): 244 hours, 34%
- Very high (300 g or more): 22 hours, 3%
Records in September 2020
- Cleanest half hour
- 63 g 12:00 on Sunday 13 September
- Dirtiest half hour
- 332 g 21:30 on Tuesday 15 September
- Most wind
- 55.6% 02:30 on Saturday 26 September
- Most solar
- 28.0% 13:30 on Sunday 13 September
- Most low-carbon
- 83.0% 13:30 on Sunday 13 September
- Least gas
- 12.3% 13:00 on Sunday 13 September
- Cleanest day
- 102 g Saturday 12 September
- Dirtiest day
- 299 g Tuesday 15 September
- Windiest day
- 42.3% wind Saturday 26 September
- Sunniest day
- 8.0% solar Sunday 13 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 28 October 2026.