In January 2021, Britain's electricity averaged 219 gCO₂/kWh, in the moderate band (140–219 g). That is 18% dirtier than December 2020 (185 g), and 5% dirtier than January 2020 (209 g). Gas made 41.8% of the electricity generated, wind 20.0%, nuclear 17.1% and imports 7.7%; low-carbon sources together made 46.2%. The cleanest half hour was 78 g at 03:30 on Sunday 17 January, and the dirtiest 330 g at 06:00 on Friday 15 January. The cleanest day was Thursday 21 January (142 g on average); the windiest was Saturday 16 January (36.6% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Fri 1 Jan | 203 | 38.8% | 10.1% | 0.0% | 49.7% | 48 |
| Sat 2 Jan | 222 | 41.5% | 11.9% | 1.1% | 46.7% | 48 |
| Sun 3 Jan | 187 | 49.9% | 19.6% | 0.9% | 39.4% | 48 |
| Mon 4 Jan | 195 | 51.2% | 24.4% | 0.5% | 40.2% | 48 |
| Tue 5 Jan | 226 | 45.5% | 21.2% | 1.0% | 44.1% | 48 |
| Wed 6 Jan | 265 | 37.9% | 12.4% | 0.8% | 49.5% | 48 |
| Thu 7 Jan | 287 | 35.1% | 9.2% | 0.9% | 52.5% | 48 |
| Fri 8 Jan | 290 | 34.2% | 8.8% | 0.4% | 53.1% | 48 |
| Sat 9 Jan | 255 | 36.9% | 13.1% | 1.2% | 49.2% | 48 |
| Sun 10 Jan | 225 | 43.0% | 18.9% | 0.6% | 43.6% | 48 |
| Mon 11 Jan | 178 | 58.2% | 33.6% | 0.5% | 34.8% | 48 |
| Tue 12 Jan | 252 | 42.0% | 16.7% | 1.0% | 43.7% | 48 |
| Wed 13 Jan | 290 | 33.3% | 8.9% | 0.3% | 49.1% | 48 |
| Thu 14 Jan | 267 | 39.2% | 16.0% | 0.3% | 45.7% | 48 |
| Fri 15 Jan | 275 | 36.4% | 10.4% | 0.8% | 48.1% | 48 |
| Sat 16 Jan | 145 | 63.0% | 36.6% | 0.9% | 27.3% | 48 |
| Sun 17 Jan | 152 | 60.8% | 32.6% | 1.5% | 29.7% | 48 |
| Mon 18 Jan | 182 | 54.6% | 29.8% | 0.6% | 37.6% | 48 |
| Tue 19 Jan | 186 | 53.2% | 25.4% | 0.4% | 37.0% | 48 |
| Wed 20 Jan | 190 | 50.6% | 23.8% | 0.1% | 38.6% | 48 |
| Thu 21 Jan | 142 | 61.9% | 35.7% | 1.4% | 28.7% | 48 |
| Fri 22 Jan | 202 | 50.4% | 24.0% | 2.3% | 37.8% | 48 |
| Sat 23 Jan | 263 | 36.3% | 9.4% | 1.7% | 48.9% | 48 |
| Sun 24 Jan | 262 | 37.2% | 10.8% | 0.8% | 48.9% | 48 |
| Mon 25 Jan | 222 | 49.5% | 22.0% | 2.1% | 39.2% | 48 |
| Tue 26 Jan | 243 | 40.9% | 14.9% | 0.4% | 46.8% | 48 |
| Wed 27 Jan | 260 | 38.6% | 11.4% | 0.6% | 47.9% | 48 |
| Thu 28 Jan | 210 | 49.2% | 20.8% | 0.9% | 37.0% | 48 |
| Fri 29 Jan | 189 | 52.9% | 25.1% | 1.3% | 33.8% | 48 |
| Sat 30 Jan | 143 | 57.4% | 33.3% | 0.6% | 31.5% | 48 |
| Sun 31 Jan | 188 | 47.5% | 22.9% | 1.0% | 41.2% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in January 2021, with January 2020 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Low (70–139 g): 98 hours, 13%
- Moderate (140–219 g): 243 hours, 33%
- High (220–299 g): 363 hours, 49%
- Very high (300 g or more): 41 hours, 5%
Records in January 2021
- Cleanest half hour
- 78 g 03:30 on Sunday 17 January
- Dirtiest half hour
- 330 g 06:00 on Friday 15 January
- Most wind
- 47.3% 04:00 on Sunday 17 January
- Most solar
- 12.2% 11:30 on Friday 22 January
- Most low-carbon
- 80.0% 04:00 on Sunday 17 January
- Least gas
- 14.8% 04:00 on Sunday 17 January
- Cleanest day
- 142 g Thursday 21 January
- Dirtiest day
- 290 g Friday 8 January
- Windiest day
- 36.6% wind Saturday 16 January
- Sunniest day
- 2.3% solar Friday 22 January
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 28 October 2026.