In May 2023, Britain's electricity averaged 148 gCO₂/kWh, in the moderate band (140–219 g). That is 8% cleaner than April 2023 (161 g), and 19% cleaner than May 2022 (183 g). Gas made 35.2% of the electricity generated, wind 20.8%, nuclear 16.3% and imports 16.2%; low-carbon sources together made 48.7%. The cleanest half hour was 45 g at 13:30 on Monday 29 May, and the dirtiest 265 g at 04:30 on Thursday 11 May. The cleanest day was Monday 29 May (76 g on average); the windiest was Thursday 4 May (48.9% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Mon 1 May | 145 | 47.1% | 20.5% | 6.1% | 31.5% | 48 |
| Tue 2 May | 219 | 33.5% | 9.4% | 5.6% | 51.6% | 48 |
| Wed 3 May | 161 | 51.8% | 24.7% | 8.8% | 38.5% | 48 |
| Thu 4 May | 95 | 72.1% | 48.9% | 5.8% | 21.2% | 48 |
| Fri 5 May | 159 | 52.0% | 27.6% | 5.7% | 37.1% | 48 |
| Sat 6 May | 193 | 37.8% | 15.7% | 3.9% | 44.9% | 48 |
| Sun 7 May | 143 | 44.8% | 17.7% | 7.6% | 32.1% | 48 |
| Mon 8 May | 134 | 54.9% | 31.9% | 2.9% | 30.8% | 48 |
| Tue 9 May | 194 | 36.9% | 12.5% | 5.2% | 46.5% | 48 |
| Wed 10 May | 196 | 38.3% | 13.1% | 6.6% | 47.8% | 48 |
| Thu 11 May | 229 | 31.0% | 5.6% | 6.7% | 56.0% | 48 |
| Fri 12 May | 155 | 53.0% | 29.4% | 4.8% | 36.6% | 48 |
| Sat 13 May | 142 | 47.7% | 21.1% | 8.2% | 32.8% | 48 |
| Sun 14 May | 155 | 42.2% | 15.1% | 8.2% | 37.3% | 48 |
| Mon 15 May | 126 | 58.5% | 33.3% | 8.3% | 30.2% | 48 |
| Tue 16 May | 143 | 48.3% | 24.2% | 8.1% | 33.6% | 48 |
| Wed 17 May | 198 | 35.7% | 11.3% | 7.4% | 47.5% | 48 |
| Thu 18 May | 180 | 40.3% | 14.3% | 7.7% | 42.3% | 48 |
| Fri 19 May | 183 | 36.4% | 12.3% | 6.7% | 45.1% | 48 |
| Sat 20 May | 103 | 52.4% | 20.2% | 11.4% | 23.1% | 48 |
| Sun 21 May | 103 | 54.2% | 20.9% | 11.0% | 23.3% | 48 |
| Mon 22 May | 117 | 62.0% | 33.9% | 8.0% | 29.6% | 48 |
| Tue 23 May | 134 | 51.8% | 23.4% | 7.8% | 33.8% | 48 |
| Wed 24 May | 153 | 50.1% | 19.1% | 9.8% | 39.1% | 48 |
| Thu 25 May | 156 | 43.1% | 12.6% | 8.4% | 39.8% | 48 |
| Fri 26 May | 145 | 46.6% | 12.6% | 10.4% | 36.4% | 48 |
| Sat 27 May | 98 | 59.7% | 21.9% | 12.0% | 22.7% | 48 |
| Sun 28 May | 85 | 60.3% | 22.9% | 10.7% | 19.2% | 48 |
| Mon 29 May | 76 | 62.9% | 24.9% | 11.8% | 17.2% | 48 |
| Tue 30 May | 118 | 54.0% | 21.8% | 8.6% | 28.2% | 48 |
| Wed 31 May | 142 | 50.0% | 20.8% | 6.4% | 34.2% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in May 2023, with May 2022 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Very low (under 70 g): 35 hours, 5%
- Low (70–139 g): 307 hours, 41%
- Moderate (140–219 g): 353 hours, 47%
- High (220–299 g): 50 hours, 7%
Records in May 2023
- Cleanest half hour
- 45 g 13:30 on Monday 29 May
- Dirtiest half hour
- 265 g 04:30 on Thursday 11 May
- Most wind
- 56.0% 23:00 on Wednesday 3 May
- Most solar
- 34.3% 13:00 on Monday 29 May
- Most low-carbon
- 84.0% 11:00 on Thursday 4 May
- Least gas
- 9.5% 11:00 on Thursday 4 May
- Cleanest day
- 76 g Monday 29 May
- Dirtiest day
- 229 g Thursday 11 May
- Windiest day
- 48.9% wind Thursday 4 May
- Sunniest day
- 12.0% solar Saturday 27 May
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 23 October 2026.