In March 2021, Britain's electricity averaged 185 gCO₂/kWh, in the moderate band (140–219 g). That is 3% dirtier than February 2021 (179 g), and 2% cleaner than March 2020 (189 g). Gas made 39.9% of the electricity generated, wind 22.1%, nuclear 15.0% and biomass 8.8%; low-carbon sources together made 51.5%. The cleanest half hour was 56 g at 13:30 on Monday 29 March, and the dirtiest 345 g at 19:30 on Friday 5 March. Sunday 28 March was both the cleanest day (72 g on average) and the windiest (47.5% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Mon 1 Mar | 276 | 30.3% | 5.3% | 2.8% | 57.8% | 48 |
| Tue 2 Mar | 292 | 28.8% | 3.5% | 2.5% | 58.1% | 48 |
| Wed 3 Mar | 311 | 25.0% | 1.8% | 1.0% | 61.8% | 48 |
| Thu 4 Mar | 258 | 33.7% | 10.9% | 1.0% | 57.1% | 48 |
| Fri 5 Mar | 280 | 32.8% | 8.8% | 2.1% | 55.5% | 48 |
| Sat 6 Mar | 277 | 28.9% | 4.3% | 3.2% | 60.4% | 48 |
| Sun 7 Mar | 263 | 32.2% | 5.4% | 4.0% | 57.4% | 48 |
| Mon 8 Mar | 252 | 36.9% | 11.3% | 2.9% | 53.4% | 48 |
| Tue 9 Mar | 209 | 45.9% | 18.4% | 4.3% | 48.0% | 48 |
| Wed 10 Mar | 135 | 64.3% | 39.0% | 0.7% | 29.8% | 48 |
| Thu 11 Mar | 109 | 69.2% | 39.2% | 4.1% | 23.2% | 48 |
| Fri 12 Mar | 105 | 69.9% | 39.4% | 4.0% | 22.2% | 48 |
| Sat 13 Mar | 95 | 70.7% | 40.3% | 4.7% | 20.7% | 48 |
| Sun 14 Mar | 98 | 72.4% | 42.6% | 3.3% | 21.0% | 48 |
| Mon 15 Mar | 188 | 51.4% | 22.1% | 3.6% | 40.6% | 48 |
| Tue 16 Mar | 174 | 54.4% | 25.3% | 3.2% | 38.6% | 48 |
| Wed 17 Mar | 193 | 50.5% | 22.1% | 3.2% | 41.6% | 48 |
| Thu 18 Mar | 210 | 46.5% | 18.3% | 2.3% | 47.6% | 48 |
| Fri 19 Mar | 237 | 39.5% | 9.3% | 3.1% | 51.3% | 48 |
| Sat 20 Mar | 206 | 41.4% | 13.1% | 2.4% | 48.9% | 48 |
| Sun 21 Mar | 196 | 44.9% | 14.7% | 3.6% | 45.0% | 48 |
| Mon 22 Mar | 226 | 40.4% | 8.8% | 4.2% | 50.6% | 48 |
| Tue 23 Mar | 164 | 56.9% | 24.7% | 3.7% | 35.8% | 48 |
| Wed 24 Mar | 150 | 60.4% | 27.0% | 4.4% | 33.3% | 48 |
| Thu 25 Mar | 121 | 65.1% | 30.4% | 4.5% | 25.1% | 48 |
| Fri 26 Mar | 98 | 71.2% | 40.5% | 3.7% | 20.9% | 48 |
| Sat 27 Mar | 83 | 76.7% | 41.0% | 5.5% | 16.8% | 48 |
| Sun 28 Mar | 72 | 80.7% | 47.5% | 2.7% | 14.3% | 46 |
| Mon 29 Mar | 89 | 76.3% | 40.4% | 6.1% | 17.7% | 48 |
| Tue 30 Mar | 156 | 57.3% | 19.4% | 7.0% | 34.6% | 48 |
| Wed 31 Mar | 197 | 44.6% | 10.6% | 5.0% | 45.8% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in March 2021, with March 2020 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Very low (under 70 g): 28 hours, 4%
- Low (70–139 g): 223 hours, 30%
- Moderate (140–219 g): 224 hours, 30%
- High (220–299 g): 223 hours, 30%
- Very high (300 g or more): 46 hours, 6%
Records in March 2021
- Cleanest half hour
- 56 g 13:30 on Monday 29 March
- Dirtiest half hour
- 345 g 19:30 on Friday 5 March
- Most wind
- 54.6% 04:30 on Sunday 14 March
- Most solar
- 24.7% 13:00 on Tuesday 30 March
- Most low-carbon
- 87.4% 07:00 on Sunday 28 March
- Least gas
- 10.3% 13:30 on Sunday 28 March
- Cleanest day
- 72 g Sunday 28 March
- Dirtiest day
- 311 g Wednesday 3 March
- Windiest day
- 47.5% wind Sunday 28 March
- Sunniest day
- 7.0% solar Tuesday 30 March
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.