In April 2021, Britain's electricity averaged 200 gCO₂/kWh, in the moderate band (140–219 g). That is 8% dirtier than March 2021 (185 g), and 19% dirtier than April 2020 (168 g). Gas made 46.0% of the electricity generated, nuclear 16.6%, wind 14.7% and imports 7.6%; low-carbon sources together made 45.7%. The cleanest half hour was 38 g at 13:00 on Monday 5 April, and the dirtiest 308 g at 06:30 on Tuesday 20 April. Monday 5 April was both the cleanest day (75 g on average) and the windiest (43.7% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Thu 1 Apr | 158 | 54.0% | 23.2% | 4.3% | 36.9% | 48 |
| Fri 2 Apr | 161 | 51.3% | 18.1% | 6.3% | 38.4% | 48 |
| Sat 3 Apr | 165 | 50.8% | 17.6% | 5.3% | 38.9% | 48 |
| Sun 4 Apr | 115 | 64.8% | 27.0% | 9.1% | 27.4% | 48 |
| Mon 5 Apr | 75 | 77.5% | 43.7% | 7.6% | 16.8% | 48 |
| Tue 6 Apr | 110 | 68.6% | 38.1% | 6.0% | 25.2% | 48 |
| Wed 7 Apr | 188 | 50.3% | 21.0% | 3.9% | 43.1% | 48 |
| Thu 8 Apr | 160 | 59.6% | 30.0% | 4.2% | 38.0% | 48 |
| Fri 9 Apr | 193 | 48.0% | 17.9% | 4.5% | 44.8% | 48 |
| Sat 10 Apr | 215 | 39.5% | 9.8% | 4.2% | 50.7% | 48 |
| Sun 11 Apr | 197 | 44.1% | 10.3% | 6.4% | 45.8% | 48 |
| Mon 12 Apr | 248 | 37.6% | 5.3% | 5.3% | 52.7% | 48 |
| Tue 13 Apr | 269 | 33.7% | 1.5% | 5.6% | 55.9% | 48 |
| Wed 14 Apr | 268 | 33.6% | 2.5% | 5.4% | 57.0% | 48 |
| Thu 15 Apr | 246 | 37.1% | 6.0% | 6.2% | 56.2% | 48 |
| Fri 16 Apr | 245 | 37.9% | 5.4% | 6.1% | 52.2% | 48 |
| Sat 17 Apr | 218 | 38.1% | 6.3% | 9.2% | 51.5% | 48 |
| Sun 18 Apr | 227 | 37.5% | 6.6% | 8.2% | 51.5% | 48 |
| Mon 19 Apr | 263 | 36.0% | 5.6% | 7.6% | 58.2% | 45 |
| Tue 20 Apr | 262 | 34.4% | 4.8% | 6.2% | 60.1% | 48 |
| Wed 21 Apr | 214 | 45.2% | 15.7% | 5.5% | 50.3% | 48 |
| Thu 22 Apr | 226 | 40.1% | 8.3% | 8.3% | 52.8% | 48 |
| Fri 23 Apr | 222 | 38.0% | 7.3% | 8.5% | 52.1% | 48 |
| Sat 24 Apr | 175 | 47.6% | 14.3% | 9.2% | 41.8% | 48 |
| Sun 25 Apr | 161 | 51.2% | 17.5% | 8.9% | 38.9% | 48 |
| Mon 26 Apr | 199 | 43.7% | 14.4% | 7.0% | 47.1% | 48 |
| Tue 27 Apr | 210 | 43.6% | 15.3% | 4.2% | 49.1% | 48 |
| Wed 28 Apr | 182 | 49.6% | 25.5% | 2.9% | 43.1% | 48 |
| Thu 29 Apr | 207 | 43.4% | 15.9% | 4.8% | 48.3% | 48 |
| Fri 30 Apr | 242 | 35.4% | 4.8% | 5.2% | 55.3% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in April 2021, with April 2020 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Very low (under 70 g): 15 hours, 2%
- Low (70–139 g): 88 hours, 12%
- Moderate (140–219 g): 326 hours, 45%
- High (220–299 g): 284 hours, 40%
- Very high (300 g or more): 7 hours, 1%
Records in April 2021
- Cleanest half hour
- 38 g 13:00 on Monday 5 April
- Dirtiest half hour
- 308 g 06:30 on Tuesday 20 April
- Most wind
- 53.5% 23:30 on Sunday 4 April
- Most solar
- 30.6% 13:30 on Sunday 4 April
- Most low-carbon
- 86.1% 14:30 on Monday 5 April
- Least gas
- 8.0% 13:30 on Monday 5 April
- Cleanest day
- 75 g Monday 5 April
- Dirtiest day
- 269 g Tuesday 13 April
- Windiest day
- 43.7% wind Monday 5 April
- Sunniest day
- 9.2% solar Saturday 17 April
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.