What is carbon intensity and why does it matter?

Carbon intensity measures the amount of C0₂ emitted to produce the electricity we use. Think of it as a score—where lower is better—that tells us how many grammes of C0₂ are released based on the mix of energy sources generating electricity at any given moment.

Electricity grids are supplied from various sources, including wind, gas, nuclear, biomass, solar, and hydro. The proportion of these sources is constantly shifting, which means the amount of C0₂ emitted also fluctuates.

Renewable sources like solar and wind don’t produce CO₂ when generating electricity, as they don’t rely on fuel. On the other hand, fossil fuels like gas and coal release CO₂ when burned for power.

Understanding the carbon intensity of your electricity allows you to make more informed decisions, such as when to run energy-intensive appliances to reduce your carbon footprint. It also helps track progress toward a carbon-free grid by analyzing historical data, which can inform future strategies for reducing emissions across other sectors through electrification.

Reducing emissions over time with more stringent goals

To ensure the focus on fully decarbonising the grid by 2030, carbon intensity goals are reduced every year.

Carbon intensity is broken down into 5 classifications; very low, low, moderate, high and very high. In 2025, a very low classification is from 0 to 29 grammes CO₂ / kWh. Once the upper limit of a classification is exceeded the electricity for that grid area moves into the next upper band.

As the percentage of wind and solar supplying electricity to the grid increases at any given time, we expect the classification to move towards one of the lower bands. Conversely, when more fossil fuel gas is used, we expect the classification to move into the higher bands.

How much carbon is emitted by different electricity generation sources?

Different electricity generation sources emit different amounts of CO₂. The 2024 definition of very low carbon intensity is < 35 grammes of CO₂ per kWh. But how many grammes is emitted by each source? What can be used to create clean electricity and what needs to be retired as a generation source? The table below shows the general emissions for each source.

Source: adapted from the Carbon Intensity project of the National Grid Electricity System Operator Methodology document