Comment by Dr Richard Snape, Senior Modelling Consultant at Energy Systems Catapult.

What will household demand look like on the coldest days when our homes are heated by heat pumps? We’ve been using data from our Living Lab to investigate. By understanding this, we can forecast peak loads and make sure our energy networks and planning standards are up to the challenge. Because when everyone cranks up their heating at once, it’s not just about having enough energy in the tank, it’s about being able to deliver it exactly when and where it is most needed.

The electrification of home heating and personal transport is increasing demand, leading to a change in the daily demand profile. Additionally, electricity demand will become more closely linked with the weather, because the colder it gets, the more energy it takes to heat our homes.

We collected data from the Living Lab for November 2024 when the temperature dropped suddenly. Figure one shows that as the temperature falls (shown by the black line), the electricity usage in homes who have told us they have a heat pump (the pink bars) increases substantially. In contrast, in homes with gas heating (the blue bars), the electricity usage only increases by a small amount.

The contrast is clear – in a typical house with gas heating today, the outside temperature has only a weak impact on electricity consumption. In homes with a heat pump, electricity consumption is strongly related to the weather.

Taking a closer look at the daytime demand profile by comparing two days one week apart, we see an additional effect combining with the overall increase in total consumption.  We compared two Thursdays just seven days apart; 14 November, when the temperature was on average 8.7°C across Great Britain, and Thursday 21 November when the average temperature dropped to 0.5°C.

In homes with gas heating, the electricity demand profile across the day was fairly flat from 6am until 4pm with an increase in demand in the evening. The evening peak is slightly higher on the colder day, but the overall profile looks very similar. The 8° drop in temperature hasn’t changed the broad profile shape and has had only a small impact on the peak demand.

Homes with heat pumps have a very different profile. On the colder day, overall demand is higher, but the shape of the profile has changed. More electricity is used across the morning to heat the home. The minimum demand happens at midday which is almost three times as high as the previous week, and more electricity is consumed in the afternoon ramping up to the evening peak. On the colder day we can see the heat pump is on for more hours of the day and at a higher loading. On a cold day, on a street where every home has a heat pump, we would expect to see all the heat pumps running for most hours across the day, at or near capacity with very little diversity of demand between each home.

Even during our milder winters, like 2024 when this data was gathered, we are starting to observe our electricity demand changing with the electrification of heat. As we electrify more heat, we can expect to see the relationship between demand and weather become stronger.

What about when it’s even colder?

We’ve also done modelling work looking at the effects of heat pump demand in a ‘one in twenty year’ low temperature scenario. Gas networks are required to consider these extreme scenarios in capacity planning. The same requirement does not apply to electricity networks.

Working with UKPN on the Neighbourhood Green project, we did exploratory work in collaboration with PNDC using our Whole Energy Systems Accelerator (WESA) tool for exploring future system scenarios, and data from Living Lab homes with heat pumps.

The project showed that during a one in twenty year low temperature, demand increases substantially and flexibility from heat pumps is limited as they are working hard. We concluded that the way electricity distribution networks plan for heat demand will need to evolve. More work is needed to understand the full relationship between network load and very low temperatures in our heat pump future. Download the reports for more detailed information.

What do we need to do?

We must update our security‐of‐supply and network‐planning standards to match the realities of electrified heating and the extreme peaks that come with bitterly cold weather.

That means sending clear market signals and incentives for very long‐duration storage, such as hydrogen stores and generation, to smooth out year‐to‐year demand swings and guarantee power when everyone’s heat pumps kick in. And evolving the way we plan distribution networks in tandem with changes based on security of supply. From low‐voltage feeders up through the transmission network, we need to plan capacity not for an average winter, but instead for new demand patterns coupled with the coldest temperatures on record. That way, the energy we produce can reach every home when it’s needed most.