Trial participants were on OVO’s Heat Pump Plus tariff add-on, giving them access to electricity for their heat pump for just 15p/kWh. Heat Pump Plus is already a market-leading rate for heating, but this trial sought to inform the development of other new tariffs that could reduce customer heating costs further.

Previous research from Nesta, such as HeatFlex, has focused on whether demand can be shifted, in a manner acceptable to homeowners, using pre-heating ‘events’. Modelling conducted during our work with Cornwall Insight has also shown that households with heat pumps could make significant savings by changing to a ‘time of use’ tariff. This project stood to bridge the gap between these two pieces of prior research and quantify the role that heat pump flexibility and innovative tariff design could have in heat pump affordability.

Currently, running costs are considered to be the second biggest barrier to heat pump adoption in the UK. We would theorise that if the tariff is appealing to customers and is commercially viable, the increase in consumer awareness (due to other work Nesta is doing) and the decrease in running costs could be a significant enabler for heat pump adoption.

The Demand Flexibility Service (DFS), introduced by National Grid ESO in 2022, rewards households for reducing electricity use at specified times. The energy system operator (ESO) has committed to further rounds of the DFS for the coming three winters, and for the first time suppliers will be able to ‘stack’ DFS payments with other services and incentives offered by distribution network operators (DNOs). This could increase the value of flexibility to consumers, further bringing down running costs.

The impact on efficiency (sCOP - a metric that measures how efficient a heat pump is over a heating season) from flexibly using a heat pump is poorly understood. This research presented an opportunity to measure sCOPs and assess whether drops in system efficiency (impacting utility bills) are offset by the value of a type-of-use tariff.

Participants had their heat pumps controlled for a series of 2-4 hour events. The events consisted of a pre-heating period and a flexibility period where internal temperatures were kept within + or - 1℃ of their usual preferred temperature. Participants were not pre-notified or asked to opt into each event.

We recorded each participant’s home electricity use and their heat pump’s electricity consumption. Participants completed weekly surveys to help us understand whether they experienced any discomfort, or whether they noticed the events occurring at all.

The trial successfully automated 58 participants’ heat pumps from 6 January to 1 April.

Some of the key findings in the report were:

• We successfully managed to remotely automate our participants’ heat pumps, keeping internal temperatures within an acceptable range by preheating homes in advance of peak times.
• We found that, on average, 30% of each home’s space heating electrical demand was shifted away from the peak period between 4 pm and 7 pm.
• Participants reported high levels of satisfaction with their internal temperatures in the weekly surveys, with 88% of responses being satisfied, 7% being neutral, and only 5% dissatisfied.
• Overall, most households did not notice OVO’s control during the trial, with 60% of weekly survey responses saying that they had not noticed a difference in comfort.
• Our results were inconclusive about whether our intervention affected daily COP or total daily electrical consumption.
• Overall, households that took part in the trial had a positive experience and would feel comfortable allowing the continued automation of their heat pumps, although some expected additional incentives.