In December 2019, Britain's electricity averaged 203 gCO₂/kWh, in the moderate band (140–219 g). That is 15% cleaner than November 2019 (240 g). Gas made 33.1% of the electricity generated, wind 23.9%, nuclear 20.2% and biomass 8.2%; low-carbon sources together made 55.6%. The cleanest half hour was 96 g at 04:00 on Thursday 19 December, and the dirtiest 356 g at 15:30 on Tuesday 17 December. Sunday 8 December was both the cleanest day (119 g on average) and the windiest (40.0% wind).
Carbon intensity, day by day
Day by day, as a table
| Day | gCO₂/kWh | Low-carbon | Wind | Solar | Gas | Half hours |
|---|---|---|---|---|---|---|
| Sun 1 Dec | 231 | 47.2% | 14.0% | 1.6% | 41.2% | 48 |
| Mon 2 Dec | 263 | 44.6% | 13.9% | 1.5% | 45.7% | 48 |
| Tue 3 Dec | 258 | 46.6% | 15.2% | 1.5% | 45.1% | 48 |
| Wed 4 Dec | 253 | 50.3% | 19.2% | 1.6% | 42.3% | 48 |
| Thu 5 Dec | 228 | 57.1% | 26.9% | 0.6% | 33.9% | 48 |
| Fri 6 Dec | 180 | 64.8% | 31.3% | 0.4% | 27.0% | 48 |
| Sat 7 Dec | 151 | 68.6% | 32.3% | 0.9% | 22.5% | 48 |
| Sun 8 Dec | 119 | 76.6% | 40.0% | 1.5% | 13.9% | 48 |
| Mon 9 Dec | 195 | 59.9% | 26.7% | 1.8% | 29.7% | 48 |
| Tue 10 Dec | 178 | 63.1% | 34.1% | 0.1% | 27.0% | 48 |
| Wed 11 Dec | 219 | 57.2% | 28.3% | 0.9% | 33.2% | 48 |
| Thu 12 Dec | 253 | 47.2% | 19.7% | 0.2% | 39.7% | 48 |
| Fri 13 Dec | 217 | 50.9% | 23.2% | 0.9% | 35.6% | 48 |
| Sat 14 Dec | 147 | 65.3% | 35.1% | 1.5% | 22.2% | 48 |
| Sun 15 Dec | 176 | 59.6% | 29.8% | 1.4% | 27.3% | 48 |
| Mon 16 Dec | 252 | 45.4% | 18.3% | 0.7% | 42.1% | 48 |
| Tue 17 Dec | 318 | 34.9% | 8.8% | 0.4% | 49.7% | 48 |
| Wed 18 Dec | 221 | 50.4% | 22.1% | 0.6% | 37.2% | 48 |
| Thu 19 Dec | 183 | 60.0% | 31.6% | 0.3% | 28.1% | 48 |
| Fri 20 Dec | 223 | 51.8% | 23.3% | 0.2% | 35.5% | 48 |
| Sat 21 Dec | 210 | 51.6% | 20.6% | 0.8% | 36.6% | 48 |
| Sun 22 Dec | 228 | 46.1% | 12.4% | 1.0% | 40.8% | 48 |
| Mon 23 Dec | 158 | 61.2% | 28.8% | 1.3% | 27.4% | 48 |
| Tue 24 Dec | 200 | 52.0% | 17.8% | 0.9% | 35.1% | 48 |
| Wed 25 Dec | 211 | 50.2% | 13.2% | 1.8% | 37.0% | 48 |
| Thu 26 Dec | 148 | 63.6% | 30.6% | 0.2% | 25.4% | 48 |
| Fri 27 Dec | 181 | 56.0% | 23.4% | 0.2% | 31.8% | 48 |
| Sat 28 Dec | 148 | 64.6% | 31.1% | 0.5% | 23.4% | 48 |
| Sun 29 Dec | 132 | 69.0% | 32.9% | 1.0% | 20.8% | 48 |
| Mon 30 Dec | 172 | 60.5% | 24.7% | 1.7% | 29.5% | 48 |
| Tue 31 Dec | 240 | 46.3% | 11.5% | 0.8% | 40.2% | 48 |
What powered the grid
Each fuel's average share of the electricity generated in Great Britain in December 2019, with November 2019 beneath it for comparison. Imports count as one source, as NESO counts them.
Hours in each carbon band
- Low (70–139 g): 132 hours, 18%
- Moderate (140–219 g): 304 hours, 41%
- High (220–299 g): 285 hours, 38%
- Very high (300 g or more): 24 hours, 3%
Records in December 2019
- Cleanest half hour
- 96 g 04:00 on Thursday 19 December
- Dirtiest half hour
- 356 g 15:30 on Tuesday 17 December
- Most wind
- 46.1% 22:30 on Wednesday 18 December
- Most solar
- 9.9% 11:00 on Monday 9 December
- Most low-carbon
- 83.0% 03:00 on Sunday 8 December
- Least gas
- 10.4% 11:00 on Sunday 8 December
- Cleanest day
- 119 g Sunday 8 December
- Dirtiest day
- 318 g Tuesday 17 December
- Windiest day
- 40.0% wind Sunday 8 December
- Sunniest day
- 1.8% solar Monday 9 December
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 30 October 2026.