In September 2019, Britain's electricity averaged 178 gCO₂/kWh, in the moderate band (140–219 g). That is 2% cleaner than August 2019 (182 g). Gas made 35.1% of the electricity generated, nuclear 23.4%, wind 20.8% and biomass 6.3%; low-carbon sources together made 57.5%. The cleanest half hour was 72 g at 12:30 on Saturday 21 September, and the dirtiest 296 g at 06:00 on Thursday 19 September. Saturday 21 September was both the cleanest day (102 g on average) and the windiest (34.1% 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 | 134 | 67.7% | 22.6% | 7.9% | 27.0% | 48 |
| Mon 2 Sep | 160 | 61.8% | 22.8% | 5.1% | 29.1% | 48 |
| Tue 3 Sep | 160 | 61.9% | 23.2% | 4.3% | 31.7% | 48 |
| Wed 4 Sep | 122 | 72.0% | 32.0% | 6.0% | 21.0% | 48 |
| Thu 5 Sep | 131 | 69.4% | 31.0% | 6.2% | 23.7% | 48 |
| Fri 6 Sep | 132 | 69.2% | 33.4% | 3.5% | 24.1% | 48 |
| Sat 7 Sep | 165 | 59.6% | 19.5% | 5.1% | 33.7% | 48 |
| Sun 8 Sep | 189 | 53.6% | 10.0% | 7.1% | 37.9% | 48 |
| Mon 9 Sep | 251 | 42.1% | 9.0% | 1.6% | 49.5% | 48 |
| Tue 10 Sep | 218 | 47.5% | 11.3% | 4.3% | 42.2% | 48 |
| Wed 11 Sep | 129 | 68.6% | 32.9% | 3.5% | 23.5% | 48 |
| Thu 12 Sep | 151 | 61.1% | 25.0% | 4.1% | 28.8% | 48 |
| Fri 13 Sep | 194 | 54.7% | 16.6% | 6.7% | 36.9% | 48 |
| Sat 14 Sep | 142 | 64.6% | 23.9% | 7.7% | 26.3% | 48 |
| Sun 15 Sep | 176 | 58.7% | 21.3% | 5.3% | 34.0% | 48 |
| Mon 16 Sep | 235 | 45.4% | 12.1% | 2.9% | 46.6% | 48 |
| Tue 17 Sep | 208 | 51.8% | 15.8% | 6.2% | 42.2% | 48 |
| Wed 18 Sep | 248 | 41.3% | 5.7% | 5.6% | 50.9% | 48 |
| Thu 19 Sep | 261 | 39.2% | 4.4% | 6.2% | 52.9% | 48 |
| Fri 20 Sep | 207 | 52.0% | 13.8% | 6.7% | 41.5% | 48 |
| Sat 21 Sep | 102 | 75.3% | 34.1% | 7.4% | 19.2% | 48 |
| Sun 22 Sep | 173 | 56.5% | 21.5% | 2.6% | 35.9% | 48 |
| Mon 23 Sep | 203 | 53.8% | 20.7% | 3.2% | 42.7% | 48 |
| Tue 24 Sep | 203 | 52.0% | 20.5% | 2.4% | 44.3% | 48 |
| Wed 25 Sep | 227 | 45.9% | 14.0% | 2.5% | 46.7% | 48 |
| Thu 26 Sep | 155 | 63.0% | 29.4% | 3.8% | 30.6% | 48 |
| Fri 27 Sep | 151 | 61.5% | 26.3% | 3.0% | 30.9% | 48 |
| Sat 28 Sep | 139 | 64.7% | 27.1% | 4.0% | 26.8% | 48 |
| Sun 29 Sep | 142 | 63.0% | 28.5% | 2.4% | 28.2% | 48 |
| Mon 30 Sep | 230 | 47.3% | 15.7% | 2.3% | 45.4% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in September 2019, with August 2019 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Low (70–139 g): 212 hours, 29%
- Moderate (140–219 g): 324 hours, 45%
- High (220–299 g): 185 hours, 26%
Records in September 2019
- Cleanest half hour
- 72 g 12:30 on Saturday 21 September
- Dirtiest half hour
- 296 g 06:00 on Thursday 19 September
- Most wind
- 47.5% 23:30 on Wednesday 4 September
- Most solar
- 26.0% 12:30 on Saturday 14 September
- Most low-carbon
- 84.2% 12:30 on Saturday 21 September
- Least gas
- 13.2% 12:30 on Saturday 21 September
- Cleanest day
- 102 g Saturday 21 September
- Dirtiest day
- 261 g Thursday 19 September
- Windiest day
- 34.1% wind Saturday 21 September
- Sunniest day
- 7.9% solar Sunday 1 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 30 October 2026.