In March 2025, Britain's electricity averaged 146 gCO₂/kWh, in the moderate band (140–219 g). That is 1% cleaner than February 2025 (148 g), and 14% dirtier than March 2024 (128 g). Gas made 32.8% of the electricity generated, wind 28.7%, imports 14.5% and nuclear 12.4%; low-carbon sources together made 52.7%. The cleanest half hour was 37 g at 10:30 on Sunday 30 March, and the dirtiest 269 g at 19:30 on Wednesday 19 March. Friday 21 March was both the cleanest day (70 g on average) and the windiest (55.0% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Sat 1 Mar | 159 | 47.4% | 17.0% | 7.1% | 35.1% | 48 |
| Sun 2 Mar | 124 | 59.2% | 27.6% | 7.1% | 23.9% | 48 |
| Mon 3 Mar | 156 | 53.9% | 25.8% | 6.3% | 34.6% | 48 |
| Tue 4 Mar | 126 | 64.5% | 37.2% | 6.8% | 28.1% | 48 |
| Wed 5 Mar | 97 | 70.8% | 48.2% | 6.4% | 21.4% | 48 |
| Thu 6 Mar | 94 | 67.5% | 43.8% | 6.4% | 20.0% | 48 |
| Fri 7 Mar | 152 | 49.3% | 29.6% | 3.8% | 36.1% | 48 |
| Sat 8 Mar | 109 | 58.7% | 32.9% | 7.7% | 21.8% | 48 |
| Sun 9 Mar | 166 | 43.3% | 16.2% | 8.3% | 35.9% | 48 |
| Mon 10 Mar | 157 | 51.6% | 33.6% | 3.2% | 37.3% | 48 |
| Tue 11 Mar | 151 | 52.7% | 33.8% | 4.8% | 36.9% | 48 |
| Wed 12 Mar | 170 | 51.6% | 30.4% | 4.1% | 40.8% | 48 |
| Thu 13 Mar | 209 | 39.7% | 16.0% | 4.3% | 49.2% | 48 |
| Fri 14 Mar | 227 | 33.6% | 10.1% | 4.6% | 53.6% | 48 |
| Sat 15 Mar | 173 | 44.3% | 15.9% | 6.5% | 36.1% | 48 |
| Sun 16 Mar | 168 | 45.3% | 16.9% | 6.2% | 35.3% | 48 |
| Mon 17 Mar | 178 | 45.4% | 22.3% | 2.8% | 39.0% | 48 |
| Tue 18 Mar | 137 | 55.0% | 28.5% | 9.3% | 29.8% | 48 |
| Wed 19 Mar | 216 | 32.8% | 6.5% | 7.6% | 50.4% | 48 |
| Thu 20 Mar | 181 | 42.4% | 15.0% | 8.8% | 41.6% | 48 |
| Fri 21 Mar | 70 | 72.6% | 55.0% | 4.0% | 12.5% | 48 |
| Sat 22 Mar | 118 | 57.2% | 35.7% | 4.8% | 24.1% | 48 |
| Sun 23 Mar | 160 | 44.7% | 23.7% | 3.1% | 34.7% | 48 |
| Mon 24 Mar | 181 | 42.3% | 20.9% | 6.5% | 43.6% | 48 |
| Tue 25 Mar | 172 | 44.9% | 24.3% | 5.0% | 40.3% | 48 |
| Wed 26 Mar | 169 | 45.0% | 21.9% | 7.8% | 40.3% | 48 |
| Thu 27 Mar | 98 | 64.6% | 44.3% | 6.1% | 21.5% | 48 |
| Fri 28 Mar | 78 | 70.9% | 50.3% | 7.7% | 17.8% | 48 |
| Sat 29 Mar | 75 | 70.5% | 48.2% | 8.0% | 14.5% | 48 |
| Sun 30 Mar | 82 | 72.5% | 46.5% | 11.1% | 17.3% | 46 |
| Mon 31 Mar | 184 | 40.1% | 12.9% | 9.5% | 42.7% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in March 2025, with March 2024 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Very low (under 70 g): 81 hours, 11%
- Low (70–139 g): 236 hours, 32%
- Moderate (140–219 g): 362 hours, 49%
- High (220–299 g): 66 hours, 9%
Records in March 2025
- Cleanest half hour
- 37 g 10:30 on Sunday 30 March
- Dirtiest half hour
- 269 g 19:30 on Wednesday 19 March
- Most wind
- 72.7% 05:30 on Sunday 30 March
- Most solar
- 35.3% 13:30 on Sunday 30 March
- Most low-carbon
- 90.0% 10:30 on Sunday 30 March
- Least gas
- 4.8% 10:00 on Sunday 30 March
- Cleanest day
- 70 g Friday 21 March
- Dirtiest day
- 227 g Friday 14 March
- Windiest day
- 55.0% wind Friday 21 March
- Sunniest day
- 11.1% solar Sunday 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 20 October 2026.