In May 2020, Britain's electricity averaged 142 gCO₂/kWh, in the moderate band (140–219 g). That is 15% cleaner than April 2020 (168 g), and 32% cleaner than May 2019 (210 g). Gas made 29.2% of the electricity generated, nuclear 22.7%, wind 17.6% and imports 11.0%; low-carbon sources together made 59.8%. The cleanest half hour was 46 g at 13:30 on Sunday 24 May, and the dirtiest 238 g at 21:30 on Friday 8 May. The cleanest day was Saturday 23 May (82 g on average); the windiest was Sunday 10 May (40.1% 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 | 136 | 59.1% | 19.6% | 7.0% | 28.7% | 48 |
| Sat 2 May | 148 | 57.8% | 15.3% | 8.8% | 31.0% | 48 |
| Sun 3 May | 197 | 45.1% | 3.7% | 4.2% | 41.6% | 48 |
| Mon 4 May | 154 | 55.8% | 11.9% | 7.1% | 30.8% | 48 |
| Tue 5 May | 117 | 64.0% | 19.8% | 8.9% | 21.9% | 48 |
| Wed 6 May | 163 | 53.5% | 6.2% | 10.7% | 31.0% | 48 |
| Thu 7 May | 182 | 50.5% | 6.3% | 8.9% | 36.6% | 48 |
| Fri 8 May | 194 | 44.8% | 4.3% | 8.7% | 41.3% | 48 |
| Sat 9 May | 168 | 50.6% | 8.7% | 10.1% | 36.1% | 48 |
| Sun 10 May | 89 | 75.5% | 40.1% | 5.0% | 18.9% | 48 |
| Mon 11 May | 108 | 70.6% | 35.2% | 8.3% | 23.8% | 48 |
| Tue 12 May | 148 | 57.3% | 18.8% | 8.0% | 30.6% | 48 |
| Wed 13 May | 151 | 57.1% | 18.8% | 7.4% | 31.6% | 48 |
| Thu 14 May | 150 | 57.1% | 16.3% | 9.5% | 31.4% | 48 |
| Fri 15 May | 144 | 58.5% | 15.6% | 9.0% | 29.1% | 48 |
| Sat 16 May | 128 | 62.8% | 18.2% | 8.4% | 25.3% | 48 |
| Sun 17 May | 125 | 62.5% | 20.4% | 9.1% | 25.0% | 48 |
| Mon 18 May | 120 | 67.1% | 25.2% | 8.6% | 24.6% | 48 |
| Tue 19 May | 153 | 56.9% | 12.9% | 8.2% | 29.6% | 48 |
| Wed 20 May | 161 | 55.3% | 9.4% | 10.6% | 32.2% | 48 |
| Thu 21 May | 153 | 56.8% | 13.4% | 9.6% | 31.9% | 48 |
| Fri 22 May | 98 | 75.1% | 36.8% | 9.4% | 22.1% | 48 |
| Sat 23 May | 82 | 79.3% | 39.9% | 9.5% | 19.3% | 48 |
| Sun 24 May | 86 | 76.2% | 34.5% | 9.5% | 18.6% | 48 |
| Mon 25 May | 143 | 62.3% | 15.2% | 12.0% | 30.1% | 48 |
| Tue 26 May | 171 | 51.8% | 9.0% | 9.4% | 35.0% | 48 |
| Wed 27 May | 196 | 44.6% | 3.7% | 9.1% | 42.0% | 48 |
| Thu 28 May | 157 | 55.3% | 9.9% | 11.1% | 31.1% | 48 |
| Fri 29 May | 146 | 57.6% | 11.8% | 11.6% | 27.3% | 48 |
| Sat 30 May | 116 | 67.1% | 22.2% | 12.8% | 22.2% | 48 |
| Sun 31 May | 124 | 65.5% | 23.0% | 12.7% | 24.0% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in May 2020, with May 2019 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Very low (under 70 g): 11 hours, 1%
- Low (70–139 g): 348 hours, 47%
- Moderate (140–219 g): 374 hours, 50%
- High (220–299 g): 12 hours, 2%
Records in May 2020
- Cleanest half hour
- 46 g 13:30 on Sunday 24 May
- Dirtiest half hour
- 238 g 21:30 on Friday 8 May
- Most wind
- 50.2% 00:30 on Monday 11 May
- Most solar
- 35.5% 13:00 on Saturday 30 May
- Most low-carbon
- 87.2% 13:30 on Sunday 24 May
- Least gas
- 10.3% 13:30 on Sunday 24 May
- Cleanest day
- 82 g Saturday 23 May
- Dirtiest day
- 197 g Sunday 3 May
- Windiest day
- 40.1% wind Sunday 10 May
- Sunniest day
- 12.8% solar Saturday 30 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 29 October 2026.