What if households could support a lower-carbon power grid by shifting the energy demand of their heat pump away from peak times?
That’s the question we’ve been looking to answer as part of a project called HeatFlex, in partnership with the Centre for Net Zero – a research unit founded by Octopus Energy.
As the UK transitions to low-carbon alternatives for domestic home heating, such as heat pumps, the demand for electricity will grow. This means that electricity capacity, transmission and distribution will need upgrading. Using heat pumps flexibly could help reduce household consumption during periods of peak demand, reducing the need for expensive upgrades to the grid. Reducing the grid’s reliance on fossil fuels at peak times could also cut carbon emissions.
In the last two years, we developed an event-based intervention, during which we remotely controlled participants’ heat pumps for four hours during ‘HeatFlex events’. Our intervention had two novel features: (i) the demand shifting was fully automated, so occupants did not have to take any ongoing action; and (ii) it sought to keep household temperatures at an acceptable level by preheating homes.
We hypothesised that the two features – automation and preheating – could result in high levels of participation, resulting in a more consistent, widespread amount of demand shifted. This, in turn, could result in a large aggregated reduction in peak electricity demand due to the high number of households that would be willing to provide flexibility.
HeatFlex – a randomised controlled trial to explore heat pump flexibility
To help us understand the extent to which we were able to shift household consumption, we evaluated our developed approach with a randomised controlled trial from February to April 2024. The trial included 43 households with heat pumps across the UK. Across 30 ‘HeatFlex events’, we remotely controlled half of our participants’ heat pumps for four hours (the other half did not take part in events).
We aimed to explore three key research areas:
- Thermal comfort of participants – do we find evidence that internal temperatures were maintained with an acceptable level during events?
- Acceptability of our intervention (ie, automation of heating systems) – how acceptable do participants find the automation of their heating systems?
- Demand reduction achieved during events – does our intervention result in changes in household electricity consumption?
Summary of main findings
Our main findings are:
- A reduction in household electricity consumption of 0.123 kWh per half-hour (p = .003) during the flexibility window (when we directed the heat pumps to produce less heat). This is a 32% reduction in typical consumption (specifically, the average household electricity consumption of our Control group at the same time).
- A reduction in heat pump electricity consumption of 0.382 kWh per half-hour (p < .001) during the flexibility window. This is a 74% reduction of typical consumption. We believe the above whole-household consumption reduction is smaller in magnitude than this heat-pump-specific consumption reduction partly because many of our participants have solar photovoltaics and batteries. These reduce whole-household consumption during the periods of the day when we typically hold HeatFlex events for both the Treatment and Control groups, reducing the effect of our intervention.
- Broad acceptance of automation from participants. Participants were happy to take part in events and for their heating to be automated. Participation in events was high: in only 9% of instances (n = 36) did participants opt out of events before they started, which was typically because they were not going to be at home.
- Participants were comfortable with the internal temperature of their homes. We found that, on average, the internal temperature in the homes of those who took part in HeatFlex events increased by 0.85oC during the two hours when we preheated homes before turning down the heat pumps for two hours. The internal temperature was still on average 0.16oC higher at the end of that second two-hour period, compared to the start of the preheating period. The majority of participants were happy with the internal temperature of their home: in 81% (n = 348) of the 428 responses in our post-event surveys (across all 30 events), participants said that they were either “Satisfied” or “Very satisfied” with the temperature in their home.
