In August 2021, Britain's electricity averaged 182 gCO₂/kWh, in the moderate band (140–219 g). That is 13% cleaner than July 2021 (208 g), and 10% cleaner than August 2020 (202 g). Gas made 35.9% of the electricity generated, wind 19.4%, nuclear 16.1% and imports 15.0%; low-carbon sources together made 47.6%. The cleanest half hour was 69 g at 14:30 on Friday 13 August, and the dirtiest 275 g at 20:30 on Monday 2 August. Friday 13 August was both the cleanest day (108 g on average) and the windiest (44.2% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Sun 1 Aug | 219 | 38.5% | 9.9% | 5.1% | 42.7% | 48 |
| Mon 2 Aug | 240 | 33.8% | 3.9% | 4.8% | 47.5% | 48 |
| Tue 3 Aug | 239 | 36.0% | 3.3% | 6.4% | 45.8% | 48 |
| Wed 4 Aug | 225 | 40.1% | 7.2% | 6.9% | 40.9% | 48 |
| Thu 5 Aug | 149 | 55.4% | 28.8% | 4.0% | 27.0% | 48 |
| Fri 6 Aug | 129 | 60.6% | 37.0% | 5.6% | 23.5% | 48 |
| Sat 7 Aug | 129 | 63.1% | 36.8% | 5.0% | 24.5% | 48 |
| Sun 8 Aug | 110 | 66.9% | 41.5% | 4.7% | 21.2% | 48 |
| Mon 9 Aug | 183 | 48.2% | 20.4% | 5.3% | 34.4% | 48 |
| Tue 10 Aug | 221 | 38.7% | 9.0% | 6.6% | 43.5% | 48 |
| Wed 11 Aug | 203 | 44.9% | 17.0% | 4.9% | 35.8% | 48 |
| Thu 12 Aug | 162 | 53.7% | 26.5% | 5.1% | 29.4% | 48 |
| Fri 13 Aug | 108 | 69.3% | 44.2% | 5.1% | 16.8% | 48 |
| Sat 14 Aug | 163 | 55.4% | 27.0% | 5.7% | 30.5% | 48 |
| Sun 15 Aug | 176 | 48.3% | 19.2% | 5.0% | 33.8% | 48 |
| Mon 16 Aug | 133 | 59.5% | 34.6% | 4.2% | 28.3% | 48 |
| Tue 17 Aug | 143 | 57.4% | 32.9% | 2.9% | 28.3% | 48 |
| Wed 18 Aug | 163 | 50.8% | 25.4% | 3.7% | 35.0% | 48 |
| Thu 19 Aug | 240 | 33.5% | 6.2% | 4.0% | 48.4% | 48 |
| Fri 20 Aug | 228 | 34.9% | 7.4% | 3.3% | 48.0% | 48 |
| Sat 21 Aug | 212 | 37.7% | 10.5% | 2.6% | 45.1% | 48 |
| Sun 22 Aug | 207 | 38.0% | 7.6% | 5.2% | 44.8% | 48 |
| Mon 23 Aug | 212 | 38.0% | 10.4% | 4.7% | 45.0% | 48 |
| Tue 24 Aug | 217 | 38.8% | 10.2% | 5.7% | 43.5% | 48 |
| Wed 25 Aug | 200 | 41.3% | 11.0% | 5.1% | 42.2% | 48 |
| Thu 26 Aug | 155 | 53.2% | 23.3% | 5.1% | 31.7% | 48 |
| Fri 27 Aug | 200 | 41.1% | 11.8% | 4.1% | 41.9% | 48 |
| Sat 28 Aug | 158 | 51.1% | 16.4% | 6.3% | 32.5% | 48 |
| Sun 29 Aug | 160 | 52.4% | 18.7% | 5.2% | 31.2% | 48 |
| Mon 30 Aug | 166 | 50.8% | 23.0% | 2.4% | 32.7% | 48 |
| Tue 31 Aug | 187 | 45.8% | 20.6% | 2.4% | 38.0% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in August 2021, with August 2020 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Very low (under 70 g): 1 hours, 0%
- Low (70–139 g): 160 hours, 22%
- Moderate (140–219 g): 389 hours, 52%
- High (220–299 g): 195 hours, 26%
Records in August 2021
- Cleanest half hour
- 69 g 14:30 on Friday 13 August
- Dirtiest half hour
- 275 g 20:30 on Monday 2 August
- Most wind
- 55.2% 05:30 on Monday 16 August
- Most solar
- 19.7% 13:00 on Wednesday 4 August
- Most low-carbon
- 78.6% 03:30 on Monday 16 August
- Least gas
- 10.1% 14:30 on Friday 13 August
- Cleanest day
- 108 g Friday 13 August
- Dirtiest day
- 240 g Monday 2 August
- Windiest day
- 44.2% wind Friday 13 August
- Sunniest day
- 6.9% solar Wednesday 4 August
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.