In July 2021, Britain's electricity averaged 208 gCO₂/kWh, in the moderate band (140–219 g). That is 22% dirtier than June 2021 (171 g), and 12% dirtier than July 2020 (185 g). Gas made 40.7% of the electricity generated, nuclear 15.7%, imports 15.0% and wind 12.1%; low-carbon sources together made 42.3%. The cleanest half hour was 83 g at 02:30 on Thursday 29 July, and the dirtiest 283 g at 22:00 on Thursday 22 July. Thursday 29 July was both the cleanest day (126 g on average) and the windiest (36.5% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Thu 1 Jul | 211 | 40.2% | 8.8% | 7.0% | 43.2% | 48 |
| Fri 2 Jul | 237 | 35.2% | 3.5% | 6.3% | 45.9% | 48 |
| Sat 3 Jul | 190 | 44.9% | 14.5% | 4.2% | 38.0% | 48 |
| Sun 4 Jul | 182 | 46.8% | 15.0% | 5.4% | 35.3% | 48 |
| Mon 5 Jul | 178 | 49.6% | 18.9% | 5.2% | 34.9% | 48 |
| Tue 6 Jul | 157 | 55.7% | 26.7% | 5.0% | 28.1% | 48 |
| Wed 7 Jul | 176 | 51.1% | 22.3% | 5.2% | 34.1% | 48 |
| Thu 8 Jul | 221 | 37.3% | 7.0% | 5.8% | 45.6% | 48 |
| Fri 9 Jul | 247 | 33.1% | 2.6% | 5.3% | 48.1% | 48 |
| Sat 10 Jul | 252 | 32.4% | 2.5% | 4.6% | 47.8% | 48 |
| Sun 11 Jul | 238 | 36.6% | 4.9% | 4.7% | 43.9% | 48 |
| Mon 12 Jul | 248 | 33.6% | 3.5% | 4.0% | 48.1% | 48 |
| Tue 13 Jul | 213 | 41.0% | 9.7% | 5.6% | 42.6% | 48 |
| Wed 14 Jul | 161 | 52.8% | 21.3% | 7.0% | 31.9% | 48 |
| Thu 15 Jul | 163 | 52.9% | 22.1% | 6.3% | 33.1% | 48 |
| Fri 16 Jul | 181 | 48.9% | 14.9% | 8.5% | 35.1% | 48 |
| Sat 17 Jul | 169 | 51.4% | 15.6% | 9.6% | 32.5% | 48 |
| Sun 18 Jul | 204 | 42.7% | 6.8% | 9.4% | 39.3% | 48 |
| Mon 19 Jul | 231 | 37.2% | 3.8% | 7.7% | 45.3% | 48 |
| Tue 20 Jul | 236 | 37.0% | 3.8% | 7.6% | 45.8% | 48 |
| Wed 21 Jul | 243 | 34.0% | 2.3% | 7.4% | 48.9% | 48 |
| Thu 22 Jul | 254 | 32.5% | 2.3% | 7.2% | 49.6% | 48 |
| Fri 23 Jul | 233 | 36.9% | 8.8% | 6.7% | 45.3% | 48 |
| Sat 24 Jul | 208 | 40.7% | 15.6% | 4.3% | 43.0% | 48 |
| Sun 25 Jul | 239 | 33.6% | 6.5% | 5.0% | 47.7% | 48 |
| Mon 26 Jul | 243 | 34.5% | 4.4% | 6.4% | 47.6% | 48 |
| Tue 27 Jul | 239 | 35.4% | 7.4% | 4.4% | 46.5% | 48 |
| Wed 28 Jul | 168 | 52.8% | 23.8% | 5.3% | 31.6% | 48 |
| Thu 29 Jul | 126 | 62.6% | 36.5% | 6.1% | 24.0% | 48 |
| Fri 30 Jul | 207 | 42.2% | 18.1% | 3.4% | 42.6% | 48 |
| Sat 31 Jul | 190 | 46.1% | 20.6% | 4.7% | 35.8% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in July 2021, with July 2020 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Low (70–139 g): 58 hours, 8%
- Moderate (140–219 g): 347 hours, 47%
- High (220–299 g): 340 hours, 46%
Records in July 2021
- Cleanest half hour
- 83 g 02:30 on Thursday 29 July
- Dirtiest half hour
- 283 g 22:00 on Thursday 22 July
- Most wind
- 53.0% 03:00 on Thursday 29 July
- Most solar
- 26.7% 13:00 on Saturday 17 July
- Most low-carbon
- 75.0% 05:00 on Thursday 29 July
- Least gas
- 15.3% 00:00 on Thursday 29 July
- Cleanest day
- 126 g Thursday 29 July
- Dirtiest day
- 254 g Thursday 22 July
- Windiest day
- 36.5% wind Thursday 29 July
- Sunniest day
- 9.6% solar Saturday 17 July
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 27 October 2026.