In May 2025, Britain's electricity averaged 107 gCO₂/kWh, in the low band (70–139 g). That is 20% cleaner than April 2025 (133 g), and 14% cleaner than May 2024 (124 g). Wind made 28.4% of the electricity generated, gas 21.8%, nuclear 16.5% and imports 14.7%; low-carbon sources together made 63.5%. The cleanest half hour was 24 g at 12:00 on Thursday 29 May, and the dirtiest 235 g at 20:30 on Thursday 8 May. The cleanest day was Thursday 29 May (44 g on average); the windiest was Monday 26 May (58.3% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Thu 1 May | 160 | 51.4% | 17.4% | 11.8% | 35.1% | 48 |
| Fri 2 May | 136 | 57.1% | 22.2% | 12.3% | 29.1% | 48 |
| Sat 3 May | 75 | 69.3% | 37.4% | 11.6% | 14.0% | 48 |
| Sun 4 May | 69 | 72.5% | 43.2% | 10.2% | 13.2% | 48 |
| Mon 5 May | 99 | 62.4% | 30.8% | 9.6% | 18.4% | 48 |
| Tue 6 May | 159 | 49.3% | 13.4% | 11.9% | 32.9% | 48 |
| Wed 7 May | 180 | 45.5% | 11.3% | 10.6% | 40.6% | 48 |
| Thu 8 May | 188 | 43.8% | 11.9% | 8.9% | 42.1% | 48 |
| Fri 9 May | 152 | 52.3% | 13.8% | 13.9% | 32.2% | 48 |
| Sat 10 May | 97 | 63.6% | 24.3% | 15.7% | 18.2% | 48 |
| Sun 11 May | 83 | 67.2% | 31.6% | 13.5% | 14.5% | 48 |
| Mon 12 May | 111 | 61.0% | 25.1% | 10.4% | 23.4% | 48 |
| Tue 13 May | 115 | 60.2% | 20.4% | 13.0% | 24.6% | 48 |
| Wed 14 May | 89 | 66.0% | 26.3% | 13.4% | 18.2% | 48 |
| Thu 15 May | 102 | 62.7% | 29.7% | 9.2% | 22.2% | 48 |
| Fri 16 May | 83 | 67.3% | 30.2% | 13.9% | 17.6% | 48 |
| Sat 17 May | 88 | 64.9% | 28.0% | 13.0% | 17.6% | 48 |
| Sun 18 May | 97 | 61.5% | 24.4% | 12.2% | 19.7% | 48 |
| Mon 19 May | 144 | 52.6% | 15.4% | 10.0% | 30.6% | 48 |
| Tue 20 May | 158 | 49.8% | 8.7% | 13.4% | 34.0% | 48 |
| Wed 21 May | 122 | 58.6% | 20.8% | 10.0% | 25.3% | 48 |
| Thu 22 May | 107 | 62.9% | 24.0% | 9.9% | 19.7% | 48 |
| Fri 23 May | 120 | 59.2% | 19.4% | 12.2% | 23.5% | 48 |
| Sat 24 May | 54 | 77.6% | 49.8% | 5.6% | 10.2% | 48 |
| Sun 25 May | 51 | 86.9% | 56.4% | 10.8% | 10.7% | 48 |
| Mon 26 May | 50 | 85.7% | 58.3% | 7.6% | 10.3% | 48 |
| Tue 27 May | 90 | 69.7% | 43.9% | 4.8% | 18.0% | 48 |
| Wed 28 May | 104 | 62.9% | 24.5% | 10.5% | 19.2% | 48 |
| Thu 29 May | 44 | 84.8% | 53.5% | 7.7% | 7.1% | 48 |
| Fri 30 May | 91 | 68.6% | 33.9% | 10.3% | 17.3% | 48 |
| Sat 31 May | 86 | 70.3% | 32.0% | 11.1% | 16.1% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in May 2025, with May 2024 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Very low (under 70 g): 199 hours, 27%
- Low (70–139 g): 351 hours, 47%
- Moderate (140–219 g): 190 hours, 25%
- High (220–299 g): 5 hours, 1%
Records in May 2025
- Cleanest half hour
- 24 g 12:00 on Thursday 29 May
- Dirtiest half hour
- 235 g 20:30 on Thursday 8 May
- Most wind
- 68.4% 02:30 on Tuesday 27 May
- Most solar
- 44.5% 12:30 on Saturday 10 May
- Most low-carbon
- 96.0% 12:00 on Thursday 29 May
- Least gas
- 3.6% 09:30 on Thursday 29 May
- Cleanest day
- 44 g Thursday 29 May
- Dirtiest day
- 188 g Thursday 8 May
- Windiest day
- 58.3% wind Monday 26 May
- Sunniest day
- 15.7% solar Saturday 10 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 20 October 2026.