By Johan du Plessis, CEO at tepeo
We often focus on the massive cost savings to be had by heating a home with a ZEB vs a direct electric boiler. However I sometimes also get asked why we claim carbon savings too, which we’ll explore in part one of this two part comparison series.
UK Carbon emissions reached a new record low in 2024
In 2024, the UK’s electricity generation reached its lowest carbon intensity ever, at 124 gCO2/kWh – this means CO2 emissions per unit of electricity have decreased by over two-thirds in the last ten years from 419 gCO2/kWh in 2014, according to Carbon Brief. This is huge for our efforts to decarbonise the UK economy but there’s something much more interesting going on…
Decarbonising Heating: Direct vs. Indirect Emissions
Traditional gas boilers produce direct carbon emissions at the point of use – causing local air pollution – and have now become the biggest source of air pollution in Central London. Electric heating solutions, like heat batteries and heat pumps, don’t have any direct emissions at point of use. This is why we called our smart heat battery product the ZEB® (originally an acronym for Zero Emission Boiler) – the parallel being the use of ZEV (Zero Emission Vehicle) in the automobile sector.
However, while the use of electric heating removes the direct emissions at point of use, we still have to consider the indirect emissions in the electricity being consumed compared with the alternatives.
Timing is everything!
This is where it gets interesting.
The UK completed its coal phase-out in September 2024 and saw renewable energy generation reach a record high of 45% of the total electricity mix in 2024. Fossil fuels accounted for a record low of 29% and nuclear power contributed 13%.
As we roll out more renewable generation on the grid, the average carbon emissions of electricity are coming down but the volatility is increasing. This transformation means that increasingly the importance of efficiency is being trumped by flexibility. Check out the graph below which shows the half-hourly carbon intensity of GB electricity last year – it ranges from a low of 14 gCO2e/kWh to highs of 303gCO2e/kWh! So exactly when you decide to turn the kettle on has a massive impact on the carbon footprint of your cup of tea…
Enter the ZEB. By storing vast amounts of energy, the ZEB decouples the consumption of heating from the times when you take electricity from the grid. Our customers can choose whether to optimise ZEB charging based on cost (their tariff) or carbon (how clean the grid is at a given point in time). There’s a very strong correlation between low cost times of day and lower carbon electricity – but it’s not perfect.
A watershed moment for highly flexible electric heating
The graph below shows the implications of this volatility for the indirect carbon emissions from smart heat batteries, like the ZEB, vs direct electric and gas boilers.
In 2024 we hit a new milestone – a typical 2/3-bed semi-detached property (using 8MWh of heat per year) heated by a ZEB on smart charging would have had an average of 107 gCO2e per unit of heat! An 85% efficient gas boiler would have had twice the carbon emissions (225 gCO2e per unit of heat) AND what’s more, these emissions would have been right outside your house. Finally, even a direct electric boiler using electricity on demand would have resulted in 50% more indirect emissions (153 gCO2e) – because heating is mostly used in mornings and evenings when electricity is typically more in demand and dirtier. (This blog is focused on carbon but this home would also have saved over £1,000 in 2024 on energy costs using a ZEB vs an electric boiler).
This is a small illustration of why aside from the massive cost benefits, flexibility is an increasingly critical part of the way we approach Net Zero. In part two of this series, we’ll be exploring the cost benefits of choosing a ZEB vs. a direct electric boiler.