In May 2026, Britain's electricity averaged 122 gCO₂/kWh, in the low band (70–139 g). That is 30% dirtier than April 2026 (94 g), and 14% dirtier than May 2025 (107 g). Wind made 25.1% of the electricity generated, gas 23.1%, imports 17.9% and solar 11.5%; low-carbon sources together made 56.8%. The cleanest half hour was 32 g at 14:00 on Tuesday 12 May, and the dirtiest 226 g at 05:30 on Monday 18 May. Tuesday 19 May was both the cleanest day (64 g on average) and the windiest (52.5% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Fri 1 May | 93 | 63.7% | 25.1% | 11.5% | 14.6% | 48 |
| Sat 2 May | 123 | 54.1% | 14.2% | 10.9% | 21.6% | 48 |
| Sun 3 May | 145 | 49.5% | 13.4% | 7.1% | 26.9% | 48 |
| Mon 4 May | 166 | 45.3% | 10.7% | 7.7% | 35.4% | 48 |
| Tue 5 May | 164 | 50.1% | 15.4% | 9.1% | 34.9% | 48 |
| Wed 6 May | 151 | 52.0% | 19.6% | 8.7% | 29.8% | 48 |
| Thu 7 May | 165 | 51.7% | 20.4% | 8.5% | 34.5% | 48 |
| Fri 8 May | 171 | 46.4% | 14.4% | 10.3% | 35.3% | 48 |
| Sat 9 May | 122 | 56.9% | 18.0% | 14.0% | 20.8% | 48 |
| Sun 10 May | 89 | 67.7% | 34.5% | 12.0% | 13.7% | 48 |
| Mon 11 May | 107 | 63.6% | 33.5% | 9.0% | 21.2% | 48 |
| Tue 12 May | 78 | 69.9% | 39.0% | 10.5% | 12.9% | 48 |
| Wed 13 May | 105 | 62.4% | 31.4% | 9.5% | 18.9% | 48 |
| Thu 14 May | 103 | 60.3% | 30.9% | 9.4% | 19.4% | 48 |
| Fri 15 May | 101 | 62.3% | 34.6% | 10.1% | 19.6% | 48 |
| Sat 16 May | 146 | 46.8% | 16.8% | 9.8% | 26.4% | 48 |
| Sun 17 May | 114 | 54.8% | 22.7% | 11.5% | 19.7% | 48 |
| Mon 18 May | 176 | 42.7% | 16.4% | 7.7% | 37.6% | 48 |
| Tue 19 May | 64 | 75.1% | 52.5% | 6.4% | 10.5% | 48 |
| Wed 20 May | 80 | 72.3% | 46.4% | 8.4% | 11.2% | 48 |
| Thu 21 May | 115 | 59.8% | 30.8% | 10.7% | 21.3% | 48 |
| Fri 22 May | 106 | 60.7% | 31.3% | 14.9% | 20.0% | 48 |
| Sat 23 May | 115 | 54.9% | 23.5% | 17.0% | 21.0% | 48 |
| Sun 24 May | 129 | 51.7% | 18.0% | 18.2% | 23.7% | 48 |
| Mon 25 May | 126 | 53.6% | 17.6% | 17.1% | 22.9% | 48 |
| Tue 26 May | 159 | 47.5% | 14.9% | 14.7% | 32.9% | 48 |
| Wed 27 May | 110 | 59.4% | 27.9% | 15.4% | 20.2% | 48 |
| Thu 28 May | 85 | 67.7% | 39.7% | 14.0% | 15.4% | 48 |
| Fri 29 May | 115 | 58.7% | 30.3% | 12.3% | 21.4% | 48 |
| Sat 30 May | 138 | 48.6% | 14.5% | 17.7% | 26.2% | 48 |
| Sun 31 May | 133 | 51.0% | 20.6% | 12.1% | 24.9% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in May 2026, with May 2025 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Very low (under 70 g): 109 hours, 15%
- Low (70–139 g): 348 hours, 47%
- Moderate (140–219 g): 286 hours, 38%
- High (220–299 g): 2 hours, 0%
Records in May 2026
- Cleanest half hour
- 32 g 14:00 on Tuesday 12 May
- Dirtiest half hour
- 226 g 05:30 on Monday 18 May
- Most wind
- 63.9% 04:30 on Tuesday 19 May
- Most solar
- 45.5% 11:30 on Saturday 30 May
- Most low-carbon
- 83.4% 14:00 on Tuesday 12 May
- Least gas
- 3.7% 13:00 on Tuesday 12 May
- Cleanest day
- 64 g Tuesday 19 May
- Dirtiest day
- 176 g Monday 18 May
- Windiest day
- 52.5% wind Tuesday 19 May
- Sunniest day
- 18.2% solar Sunday 24 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 18 October 2026.