What does carbon intensity mean?
Carbon intensity is measured in grams of CO₂ equivalent per kilowatt-hour (gCO₂eq/kWh). It tells you how much greenhouse gas was emitted to generate the electricity you’re using right now. A lower number means cleaner electricity; a higher number means more fossil fuels are in the mix.
How is it calculated?
Each fuel source has a different carbon intensity factor. Wind, solar, nuclear and hydro have very low lifecycle emissions. Gas-fired power stations emit around 394 gCO₂/kWh. The grid’s overall carbon intensity is a weighted average based on how much each source is contributing to the mix at that moment.
Grid carbon intensity = (% wind × 11) + (% solar × 33) + (% nuclear × 12) + (% gas × 394) + (% biomass × 120) + (% imports × import intensity). The figures are gCO₂/kWh lifecycle emissions for each technology.
What affects the UK grid carbon intensity?
Wind speed
Wind is the single biggest driver of GB carbon intensity. When wind is high — especially offshore in the North Sea — carbon intensity can drop below 50 gCO₂/kWh. On calm days with little wind, gas turbines spin up to cover demand and intensity can exceed 200 g.
Time of day
Carbon intensity is typically lowest in the middle of the day on windy days, and highest in the early morning on cold, calm winter days when demand peaks and renewable output is low. This is why smart appliances like dishwashers and EV chargers can significantly reduce your household’s carbon footprint just by running at the right time.
Season
Summer generally has lower carbon intensity. Solar generation is higher and heating demand is lower. Winter mornings, particularly in high-pressure anticyclonic weather when winds are calm and the sun is low, typically have the highest intensity of the year.
Nuclear output
The UK’s seven nuclear stations provide steady, very low-carbon baseload power. When a reactor goes offline for maintenance, gas usually fills the gap, raising carbon intensity. Nuclear currently contributes around 12–18% of GB electricity.
UK carbon intensity in context
The GB grid has decarbonised dramatically since 2012, when coal provided 39% of electricity. The average carbon intensity has fallen from around 500 gCO₂/kWh in 2012 to under 150 g in 2025. In 2024, renewables supplied over 50% of GB electricity for the first time, and 2025 saw the first full calendar year with zero coal generation.
During periods of exceptionally high wind, especially in spring and autumn, the GB grid regularly records carbon intensity below 30 gCO₂/kWh — cleaner than almost any grid in the world at that moment. These periods are tracked live on UK Grid Live and flagged when they occur.
How to use carbon intensity to reduce your impact
- EV charging: If you’re on a smart tariff, charge overnight when wind is often high and intensity lower — or use UK Grid Live to check before plugging in.
- Washing machines & dishwashers: Running these during low-intensity windows (often midday or windy periods) can cut the carbon footprint of the wash by 50%.
- Heat pumps: Heat pump users on Agile tariffs can pre-heat their home during cheap, clean periods and coast through expensive, dirty ones.
- Businesses: Companies with flexible demand — data centres, cold storage, industrial processes — can shift load to align with low-carbon windows, reducing Scope 2 emissions.
Where does the data come from?
UK Grid Live uses the Carbon Intensity API, published jointly by the National Energy System Operator (NESO) and the University of Oxford’s Environmental Change Institute. It updates every 30 minutes with actual measured intensity, and also provides 96-hour forecasts. The API is free and open.
Check the current UK carbon intensity
UK Grid Live shows the live carbon intensity updated every 5 minutes, alongside the full generation mix driving it.
⚡ See Live Carbon Intensity