The Grid · The Clean-Hour Desk
A Kilowatt-Hour Is Not a Kilowatt-Hour
The electricity in a British socket is a blend, remixed every half hour — mostly wind in the small hours, mostly gas at dinnertime. So the same load emits wildly different amounts of CO₂ depending only on when you run it. And the grid publishes the clean window before it arrives.
— reading the grid —
◄ 24h ago · carbon intensity of every kilowatt-hour · 24h ahead ►
clean — wind, sun, nuclear, hydro
mixed
carbon-heavy — gas, coal, imports
now
Each column is one half-hour. Height and colour are the same thing: grams of CO₂ released per kilowatt-hour delivered. Left of the now line is what the grid actually did; right of it is National Grid's own forecast. The brighter band marks the cleanest hour still to come — the one worth waiting for.
What's on the grid this half-hour
Why the same socket isn't the same socket
Electricity can't be labelled. Once it's on the wires, your kettle draws from whatever is feeding the grid at that instant — and that mix never holds still. On a windy night, turbines can cover a third or more of demand and the carbon per unit falls toward the floor. At dinnertime, with the wind dropped and demand peaking, gas plants spin up to fill the gap and the carbon per unit climbs.
So a kilowatt-hour isn't a fixed quantity of pollution. It's a rate that moves with the weather and the clock, and across a single day it can swing several-fold. The figure at the top — — times — is the dirtiest half-hour shown divided by the cleanest. Same kettle, same cup of tea; that multiple is the difference between drinking it now and drinking it then.
The useful part is that the swing is predictable. Because wind and demand are forecast, so is the carbon. National Grid ESO publishes a 48-hour curve, which is why the cleanest hour ahead can be named before it gets here: —. Run the dishwasher, charge the car, or boil the kettle in that window and the identical task emits a fraction of the carbon. No new hardware. Just timing.
Source:
National Grid ESO Carbon Intensity API (Great Britain). Half-hourly actuals and 48-hour forecast; generation mix for the current settlement period. Intensity in gCO₂ per kWh. Fetched fresh on every load and every five minutes.
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