Great Britain electricity

Window 28 Jun 2026 01:00 → 05 Jul 2026 16:30 · generated 2026-07-05 16:36 · 367 (1 forecast-only)

All times UK local (Europe/London).

Over this window the grid averaged 121 gCO₂/kWh, mostly in the low band. Renewables (wind, solar, hydro) supplied 44.06% on average. It was cleanest at Sat 13:30 (37 gCO₂/kWh) and dirtiest at Tue 03:30 (256), UK time. The latest day (partial) is running cleaner than the window average (76 vs 121 gCO₂/kWh).

Average 121 mostly low ▲ 18.87 gCO₂/kWh vs prev day mean (worse)

share 44.06 % wind + solar + hydro ▼ 12.24 pp vs prev day mean (worse)

Low-carbon vs fossil 58.84 % / 24.64 % low-carbon incl. nuclear & biomass ▼ 10.17 pp low-carbon vs prev day mean (worse)

Cleanest / dirtiest half-hour 37 / 256 gCO₂/kWh cleanest 04 Jul 13:30 · dirtiest 30 Jun 03:30

(window average)

Wind29.7%
Gas24.64%
Imports13.82%
Solar12.72%
Nuclear10.17%
Biomass4.61%
Other2.7%
Hydro1.64%
Coal0.0%

Carbon intensity trend

Solid = actual · dashed = .

Time-of-day profile (mean intensity by half-hour, UK local time)

Typically cleanest around 14:00 (84 gCO₂/kWh) and dirtiest around 21:00 (159), UK local time. The shaded band is the minimum–maximum range seen across the window.

Generation mix over time (hourly average)

Wind
Gas
Imports
Solar
Nuclear
Biomass
Other
Hydro
Coal

Renewables vs carbon intensity

Pearson r = -0.923 across 367 half-hours — a strong negative correlation: more renewables, lower intensity.

Time spent in each intensity band

low 43.9% moderate 34.6% high 12.8% very high 8.7%

Latest day (partial) vs the day before

Metric	Previous	Latest (partial)	Change
intensity mean	56.77	75.65	▲ 18.87 (33.25%)
renewable share	60.15	47.91	▼ 12.24 (20.34%)
low carbon share	73.81	63.65	▼ 10.17 (13.78%)
fossil share	9.63	10.96	▲ 1.33 (13.79%)

Today is a partial day (31 of 48 half-hours); its mean covers only the half-hours so far. Baseline is the previous day's mean — distinct from the anomaly section's same-time-of-day 7-day norm.

Anomaly flags (observations to verify)

intensity deviation

Latest intensity 72 gCO2/kWh at 15:30 is 27% below the 7-day norm for this time of day (98 gCO2/kWh) — worth verifying.

fuel swing

Solar share is 20.8pp up vs its recent average (33.5% now, 12.7% typical) — worth verifying.

Records — cleanest 37 gCO₂/kWh (04 Jul 13:30) · dirtiest 256 gCO₂/kWh (30 Jun 03:30) · greenest mix 77.7% (28 Jun 14:00).

Methodology & validation

Check 1 — did we get the maths right?

100% match

We re-added every half-hour ourselves and compared our daily averages, minimums and maximums with the ones the official API publishes. They match 100% — within ±1.0 gCO₂/kWh across all 7 days. Like re-adding the line items on a restaurant bill and getting exactly the printed total.

The precise method

7/7 daily windows reconcile our recomputed mean/min/max against the API's own /intensity/stats within ±1.0 gCO₂/kWh (largest mean gap 0.4 gCO₂/kWh) — the only expected difference is that the API rounds its average to a whole number.

Check 2 — can we rebuild the number from scratch?

35.53 gCO₂/kWh mean gap

We also estimated the intensity a second, independent way: take each fuel's share of the mix and multiply by its official emissions factor. Our estimate runs about 35.53 gCO₂/kWh higher than the official figure — and that gap is expected. The official number knows things the public mix can't show: rooftop solar and small wind farms, where imports really come from, and losses in the wires. It's like estimating a restaurant bill from the menu — close, but the printed bill includes the service charge. We measure that gap and report it rather than hide it.

The precise method

Per-half-hour differences between our reconstruction and the reported figure: mean gap 35.53 (abs 35.54), spread ±16.27, range -0.64…72.17; 10 outliers flagged. The estimate can't credit , can't split by source, and treats all gas as .

Indicative only. Reconstructed as Σ(fuel_share × published_factor) using the coarse generation mix; it omits interconnector imports by source, transmission & distribution losses, and embedded (behind-meter) wind and solar, so a gap to the official figure is expected — the value is quantifying that gap, not matching it.

The gap tends to peak in daylight hours, when embedded rooftop solar — invisible to the public mix — pulls the official figure down.

Modelling choices

We show the grid's measured intensity where it's available, and the forecast for the latest half-hours that aren't final yet — the line at the top counts how many are forecast.
Biomass is counted as low-carbon (alongside nuclear, wind, solar and hydro). That's a judgement call — biomass's lifecycle emissions are debated — so we state it plainly rather than bury it.
Renewable here means wind, solar and hydro only; nuclear and biomass count as low-carbon but not renewable.
For the from-scratch estimate, gas uses the emissions factor for the efficient combined-cycle plants that supply most GB gas; the public mix can't separate the smaller peaking plants.
The public mix lumps all imports into one figure, so the estimate averages the interconnector factors — a rough proxy, and the main reason the from-scratch check is only indicative.
Charts are drawn as a <canvas> image, so each carries a text label (role="img" + aria-label) and a data-table fallback for non-visual reading.
Day-to-day changes are coloured by whether they're better or worse for grid cleanliness, not by direction — so a fall in intensity (cleaner) shows green even though its arrow points down.
The grid data is published in UTC; every time shown on this page is converted to UK local time (Europe/London, so BST in summer) — the trend and mix-over-time axes, the time-of-day profile, the cleanest/dirtiest and record times, and the window line — so daylight and the clock line up. The data and JSON API stay in UTC.

Data tables (non-visual view)

Fuel	Window share %
Wind	29.7
Gas	24.64
Imports	13.82
Solar	12.72
Nuclear	10.17
Biomass	4.61
Other	2.7
Hydro	1.64
Coal	0.0

Factor → mix mapping	gCO₂/kWh
biomass	120.0
coal	937.0
nuclear	0.0
hydro	0.0
solar	0.0
wind	0.0
other	300.0
gas	394.0
imports	328.33

Time of day (UK local)	Mean	Min	Max
00:00	135.14	64	233
00:30	134.71	63	239
01:00	134.0	63	237
01:30	132.62	65	236
02:00	130.5	64	240
02:30	129.25	68	245
03:00	129.12	66	245
03:30	131.5	66	256
04:00	132.25	62	255
04:30	133.62	63	254
05:00	133.5	63	252
05:30	131.75	70	237
06:00	130.0	67	229
06:30	127.0	64	219
07:00	124.38	58	216
07:30	118.62	53	209
08:00	113.0	48	203
08:30	108.38	51	192
09:00	102.75	49	181
09:30	100.5	50	176
10:00	98.0	48	172
10:30	95.38	47	169
11:00	91.62	46	168
11:30	89.25	45	164
12:00	86.88	42	160
12:30	85.75	41	161
13:00	84.75	41	158
13:30	85.0	37	166
14:00	84.25	37	165
14:30	84.38	38	165
15:00	87.0	39	170
15:30	95.0	41	179
16:00	100.38	42	187
16:30	111.71	41	187
17:00	120.43	43	196
17:30	132.0	49	211
18:00	139.43	55	221
18:30	144.71	60	220
19:00	149.0	61	223
19:30	154.14	65	225
20:00	157.86	71	226
20:30	158.29	68	229
21:00	159.14	72	231
21:30	154.71	65	231
22:00	151.57	60	231
22:30	143.29	68	230
23:00	139.29	64	232
23:30	137.71	64	233

Renewables vs carbon intensity — Pearson r = -0.923 across 367 half-hours — a strong negative correlation: more renewables, lower intensity. Mix-over-time and the reconstruction-gap series use the same fuels and per-half-hour figures shown in the charts above.

Carbon intensity and generation data © National Energy System Operator (NESO), via the Carbon Intensity API (carbonintensity.org.uk), used under CC BY 4.0.
Built with Chart.js (vendored locally, MIT). Dashboard generated by the GridLens engine — every number is computed in deterministic Python.