Domestic solar generation per day

Domestic solar generation is taken for the days of the 21st and 22nd of June 2026, the first two days of elevated temperatures in the late June heatwave. Domestic-scale capacity and generation is defined as those installations up to 10 kW. Naturally there are edge-cases where domestic solar installations are above 10 kW, or commercial developments are below 10 kW, which cannot be accounted for in the available data. This is therefore not an annual average for domestic generation, but based on the conditions during the heatwave.

National solar generation (average 109.7 GWh) was scaled down to the domestic solar capacity (6.3 GW) proportion of total national solar capacity (23 GW), split as estimated by Sheffield Solar, in line with the capacity bands defined above. This was on average 28.5 GWh, produced by 1.88 million domestic-scale installations in the UK, the equivalent of 15.2 kWh per day.

 

Air conditioning demand per day

Due to the nascent quality of air conditioning in UK homes, precise data on average air conditioning size is not available. Furthermore, the operation and cooling demand varies significantly by user.

The DESNZ Energy Innovation Research Office: Air-to-Air Heat Pumps Literature Review (another name for modern air conditioning units which can provide both heating and cooling) found a wide range of cooling output from available units between 3 and 12 kW. This report noted a lack of ‘real world’ data on the efficiency (coefficient of performance) of air-to-air heat pumps, with a range of 1.2 to 4.5 kW. Assuming an average heating output of 7.65 kW and an average COP of 2.85, a typical air conditioning demand can be assumed of 2.7 kW. Due to the lack of specific data, a more conservative 3.0 kW has been assumed for air conditioning demand. It is worth noting that some manufactures, such as Daikin, publish air-conditioning unit specifications which state a seasonal COP of 5.2, which would almost halve the power requirement of the unit compared to what assumed here, but we have used the figures in the DESNZ review for consistency.

Therefore, taking these assumptions altogether, the equivalent of a 3 kW air conditioning unit can be run for 5.1 hours per day based on an average 16 kWh of domestic-scale solar generation during the first two days of the heatwave. This has been conservatively rounded down to 5 hours, again due to lack of data specificity.