Predicting the additional GB electricity demand resulting from a widespread uptake of domestic heat pumps

Around 80% of domestic heat demand in Great Britain (GB) is currently supplied by natural gas, but continuing to heat dwellings in this way is unlikely to be compatible with national emission reduction targets. Electrical heating using heat pumps is expected to play a significant role in future space heating and hot water provision, although the extent of this is uncertain. The biggest challenge associated with greater use of heat pumps, or indeed any form of electric heating, is the increase in the peak electricity demand in cold weather. The increase in the annual GB electricity demand, and potential increases in the ramp rate of that demand are also significant issues.

Understanding the scale of these challenges requires an understanding of heat demand over short time intervals (e.g. half-hourly). Existing estimates of half-hourly heat pump electricity demand are derived from small samples of dwellings where the heat demand was not supplied by heat pumps. Heat pumps have a lower flow temperature and lower maximum heat output than other types of heating system, and hence are likely to be used for more hours per day, potentially leading to lower peak demand and ramp rate. The validity of the existing half-hourly demand estimates is therefore questionable.

This work investigates the future GB heat pump electricity demand using empirical modelling. This is based on the monitored use of heat pumps and gas boilers in field trials, using much larger samples of homes than previously. Differences between gas boiler and heat pump heating patterns are investigated, and models of current heat demand and possible future heat pump heat demand are produced, including the variation in sub-daily profile shape with outdoor temperature and household socio-demographic factors. Heat demand estimates are converted into electricity demand using a model of heat pump performance which includes the monitored variation in heat pump coefficient of performance with outdoor air temperature.

It was found that the current GB peak domestic heat demand in a ‘cold’ year is 170 GW, around 40% lower than previously estimated. The calculated GB maximum ramp rate of domestic heat demand was 63 GW/h, around 50% lower than previously estimated. When the differences in heating pattern between gas boilers and heat pumps were taken into account, the peak GB domestic heat demand, if 100% of that demand is met using heat pumps, was 158 GW, and the maximum ramp rate was 23 GW/h. This resulted in a peak heat pump electricity demand of 75 GW; the maximum GB electricity demand ramp rate for domestic heat provision was 11 GW/h.

Changes in peak demand and ramp rate resulting from improvements to heat pump performance, changes in heat pump heating pattern, changes in climate and changes in the mix of heat pump types were investigated. The heat pump electricity demand was added to existing GB electricity demand, and the potential of load shifting to reduce the overall peak electricity demand was also investigated. It was found that the total GB peak electricity demand was more than doubled from its current value of 60 GW to 130 GW by the addition of heat pump loads. Allowing domestic hot water demand and 20% of space heating demand to be flexible reduced the peak GB electricity demand to 109 GW.

Whilst the calculated peaks in GB domestic heat demand, and the resulting peaks in GB domestic heat pump electricity demand, are considerably lower than previously thought, the electrification of domestic heating still represents a considerable challenge. Most notably, the peaks in the GB electricity demand could be doubled when 100% of domestic heat demand is met by heat pumps.