January 5, 2024

Reducing Carbon Intensity of the National Grid

An intro to carbon intensity on the grid

Carbon intensity of the National Grid

In our first two blogs, we discussed how large commercial buildings can leverage energy flexibility to reduce their energy bills by shifting consumption outside of peak times.

By shifting consumption outside peak times, businesses can also significantly reduce the emissions of their energy use - this is down to the carbon intensity of electricity generation.

This blog explains what drives carbon intensity and how shifting energy usage can deliver meaningful CO2 reductions.

The UK energy mix:

The UK's energy mix can be quite simply categorised into two primary sources:

  1. Zero carbon: renewable energy such as wind, solar, hydro, nuclear power, and;
  2. High carbon: fossil fuels like coal, natural gas, and oil 

Put simply; renewable energy has a carbon intensity of zero, and fossil fuels range from c.400 - 900 gCO2/kWh.

Carbon intensity with changes in the energy mix:

The carbon intensity of the national grid is an output of the type of electricity on the grid. It's driven by the generation mix at various points of the day and the carbon intensity of each source.

The proportion of energy on the grid from each source changes over time due to factors like weather conditions and energy demand. And while it's great that the shift towards renewable energy sources is gaining momentum, the intermittency of renewable energy supply can create gaps in meeting instantaneous demand.

For example, wind farms in the UK produce a massive range of anything from 7% to 82% of their total capacity during peak hours, this range depends entirely on wind speeds at the time, and solar power does not provide any assistance during peak demand periods in Britain as demand peaks in winter evenings.  

This means that although renewable energy is great for having low carbon intensity, its supply is not linked closely with demand.

Fossil fuels, however, such as natural gas and coal-fired plants, can be (and often are) utilised as "peaker" plants because they can bridge these gaps and ensure a stable electricity supply - this is even more common in winter months.

During periods of high demand, when renewable energy generation might not be sufficient to meet the load, these plants respond quickly, providing a critical backstop to the grid's energy supply.  In January this year, the National Grid paid a record £27m (per day) to get peak-power stations to turn on supply at short notice.

While these peaker-power plants can provide reliable electricity for balancing demand, the carbon emissions of these plants are responsible for the peak in carbon intensity of the grid during these high-demand hours.

Our daily routines drive the carbon intensity of the grid:
Carbon Intensity Forecast UK

1. As the sun rises and people begin their day, energy demand surges due to the increased use of power-hungry appliances like heaters, kettles, and showers. Fossil fuel power plants might be brought online to meet this demand, elevating the carbon intensity temporarily.

2. Midday lull: The carbon intensity tends to dip around midday because renewable energy sources like solar and wind are at their peak generation. 

3. Evening surge: As people return home from work, turn on the TV and cook dinner, the carbon intensity surges again due to increased energy consumption.

4. Nighttime dip: carbon intensity lowers due to reduced overall demand. 

Leveraging flexibility at scale to reduce carbon intensity:

Knowing the best times to shift energy usage to achieve the most significant impact on carbon intensity is easier than you might think. The National Grid already publishes a forecast for carbon intensity using the instantaneous generation mix and weather data provided by the Met Office.

On just a consumer scale, National Grid calculations show that if one million Brits switched to using their washing machine at low carbon intense times, we could collectively help save 76,650 tonnes of CO2 each year, the equivalent of taking 36,500 cars off the road.  

If this is the impact for just one million households, think of the effect that 1.8 million commercial buildings in the UK could have.