4.3.5. Hourly Electricity Load Savings

Figure 16 shows load profiles of house archetypes and specifications for Comfy Heat and E12 tariffs for the coldest winter workday and holiday. Maximum peak loads occur as 4.05 kW in Comfy Heat tariff and 3.94 kW in E12 tariff for all archetypes in the coldest winter workday. Detached houses have the highest energy demand. Therefore, the total variable load is 27.7 kW and 28.8 kW in comfy Heat and E12 tariffs in the unrefurbished category. Semi-detached and end-terraced houses have similar total loads, approximately 19.0 kW in Comfy Heat tariff and 21.0 kW in E12 tariffs. Mid-terraced houses have the lowest total load with 16.8 kW and 18.3 kW in Comfy Heat and E12 tariffs, respectively. When houses become more energy efficient, their energy demand reduces, so lower loads are seen in efficient houses. Total heat pump loads in detached houses could be reduced to 20.4 kW in a refurbished house or 13.7 kW with a Comfy Heat tariff in a new building category. Moreover, fewer peaks occur throughout the day. A similar trend occurs in other house archetypes and total heat pump loads could be reduced to 12.7 kW, 11.3 kW, and 12.7 kW for semi-detached, mid-terraced, and end-terraced new building categories, respectively. The coldest winter holiday results also show similar trends but slightly lower load profile results.

This study tries to break down the load results into different house archetypes and specifications so cumulative electricity system load profiles would be more accurate. Each archetype profile is multiplied by the number of houses using heat pumps for all scenarios. Figure 17 shows Orkney electricity system load for baseline, RE, and CE scenarios for the coldest winter workday and holiday. The results are presented for Comfy Heat and E12 tariffs separately and their equally mixed usage scenario. Existing electric loads coming from room heaters are also presented in the figures with yellow bars. The baseline scenario has a limited number of heat pumps deployed. Therefore, the total daily variable heat

pump load is 14.4 MW and 15.4 MW for Comfy Heat and E12 tariffs with 27.9 MW and 26.3 MW peak loads in the coldest winter workday.

**Figure 16.** Average hourly electricity demand load curve of a representative heat pump profile by different archetypes and electricity tariffs for the coldest winter workday and holiday (T: Total, M: Maximum, A: Average).

**Figure 17.** Average hourly electricity demand load curve of heat pump scenarios for Orkney for the coldest winter workday and holiday (T: Total, M: Maximum, A: Average).

RE scenario has high deployment rates of heat pumps (around 80% of total dwellings) so daily total variable heat pump loads reach 168.1 MW and 181.9 MW in Comfy Heat and E12 tariffs with 59.9 MW and 54.7 MW peak loads respectively. Combining both tariffs reduces the peak load to 46.0 MW. When CE scenario has total daily variable heat pump loads with 186.2 MW in Comfy Heat tariff and 202.2 MW in E12 tariff, the peak loads reach 67.7 MW and 62.9 MW in the tariffs, respectively. Comfy Heat tariff has a smaller number of peaks but E12 tariffs have more spread around the day, so the mixed deployment of tariffs helps to reduce peaks to 51.2 MW. When variable heat pump load is compared with constant heat pump load (light red line), the majority of the variable loads stay below constant load, and heat pumps do not operate in the evening, which is when the highest baseload occurs. Peaks are happening in three periods: during the night, before evening and before midnight with two peaks in each. When the coldest holiday results are analyzed, these peaks are even less in the CE scenario with a mixed tariff setting. Only the peak happening before midnight needs to be handled.

Different tariffs create load peaks in different time periods which could be beneficial to combine electricity tariffs to have a more evenly electricity load spread throughout the day. EEI measures help to reduce the total daily variable heat pump load which is crucial to decrease energy demand. However, peak loads remain the same. Therefore, combining more than one electricity tariff in the market could help to reduce peak loads.
