ORKNEY'S ENERGY FUTURE
ROAD TRANSPORT
METHODOLOGY
INTRODUCTION
The purpose of these calculations was to calculate the hourly, daily and annual electricity demand that would arise from a complete switch from petrol and diesel cars to electric vehicles (EVs) in Orkney. The expected number of cars in Orkney was projected to 2030 using Orkney Road Traffic Statistics [1] and trends from 2009 to the present day [2] (Figure 2). The current number of cars is 11,300 and this is expected to increase to 12,792 by 2030.
Figure 1: Schematic diagram of a Volkswagen ID.4 [3].
Figure 2: The projected number of cars each year from 2020 to 2030 using the past ten-year trend in Orkney from 2009 to 2019 [2].
There has been rapid uptake in electric vehicles in Orkney in the last 10 years (Figure 3). This has resulted in an abundance of vehicle choice and a large range in price [4]. DriveElectric is a car leasing company that supplies EVs to Orkney residents through ReFLEX and data from its car collection has been used to model the electricity demand. Average specifications of the company’s five most popular EVs have been used as the basis for the calculations (Figure 4); it was deemed that this would be representative of the EV implementation in Orkney.
Figure 3: Number of electric vehicles (EV) registered in Orkney from 2000 to 2020 [5].
Figure 4: A car model comparison to show the energy efficiency and price of the vehicles considered for this analysis [4].
ELECTRICITY DEMAND
Converting all cars to EVs will increase Orkney’s electricity demand. The electricity demand for 12,792 EVs has been calculated using the average consumption of the five most popular EVs and UK charging trends. The electricity demand is based on the average annual distance travelled by a car in Orkney. Using UK charging trends, monthly, daily and hourly electricity demand profiles were produced (Table 1).
The average distance travelled by car in Orkney was calculated using 2019 Orkney Road Traffic Statistics [1]. This was found to be approximately 9.92 miles per day, resulting in an approximate annual mileage of 3,620 miles. Most of the distances travelled in Orkney are relatively short which makes EVs the ideal choice for decarbonisation [6]. The average consumption of the cars included in the analysis is 274 Wh/mile [4]. For 12,792 EVs, the annual electricity consumption was calculated to be 12.7 GWh. Since EV batteries are not 100% efficient, the electricity consumption is not equivalent to the demand. The efficiency of an EV battery can be up to 95% [7]. However, the efficiency is related to temperature, so for a location like Orkney, 90% could be expected [8]; this is the battery efficiency that was used in the calculations. The annual EV electricity demand is therefore approximately 14.1 GWh for 12,792 cars.
To validate the calculated annual electricity demand, the results were compared to reported data on charging demand in Orkney. There were 252 EVs in Orkney between 2018 and 2019. During this time, a dashboard maintained by ReFLEX shows that public charging demand was 14.8 MWh [5]. Total charging demand is a result of public and domestic charging. The magnitude of public charging is 6% that of domestic charging [8]. Therefore, the corresponding domestic charging demand would be 231.9 MWh and the total charging demand 246.7 MWh for 252 EVs. If there were 12,792 EVs, the demand would therefore be approximately 12.5 GWh which is 11% lower than the calculated annual demand of 14.1 GWh. This gives confidence in the calculated electricity demand.
Table 1: Input data and calculation methods for the electricity demand profiles.
The electricity demand increases towards the end of the year and tends to be greater during months with school holidays (Figure 5). Demand changes daily and there is greater electricity demand during weekdays (Figure 6). The pattern of hourly charging shows peak charging demand occurs between 17:00 and 18:00 (Figure 7).
Figure 5: Monthly distribution of EV electricity demand for the expected number of cars in 2030 (12,792).
Figure 6: Daily EV charging demand distributed over a week in January for the expected number of cars in 2030 (12,792).
Figure 7: Hourly charging rate for a Wednesday in January for the expected number of cars in 2030 (12,792).
To show the difference in electricity demand between domestic and public charging, EV charging trends from the UK Government [10] were used to divide the hourly electricity demand between domestic, public fast and public rapid charging. The demand profiles (Figure 8) are as expected where the peak domestic charging occurs during the evenings and the peak public charging occurs during the day and early in the morning. The domestic charging demand is about 20 times greater than the public charging demand. This shows that if Orkney was to make the switch to EVs and were to follow the same charging trends as the UK, domestic chargers would be the dominant source of electricity. If Orkney Council chose to implement EV infrastructure differently by, for example, investing in more public charging points, the distribution of EV charging could change.
Figure 8: Hourly charging rate by charger type for a Wednesday in January for the expected number of cars in 2030 (12,792).
SENSITIVITY ANALYSIS
Sensitivities on vehicle consumption (Figure 4), battery efficiency [8] and daily average mileage were considered to calculate a deterministic high and low case annual electricity demand (Table 2). The daily mileage was varied by +/- 20% and is the parameter that has the highest impact on the annual electricity demand (Figure 9). The high case annual electricity demand will be considered in relation to the Demand and Generation results.
Table 2: Parameters varied to calculate deterministic high and low case annual electricity demand.
Figure 9: Tornado diagram for parameters; number of miles driven, EV consumption and battery efficiency.
AVAILABLE DOWNLOADS
The spreadsheet with the demand calculations is available here.
REFERENCES
[1] UK Government, "Road Traffic Statistics (TRA0101)," September 2020. [Online]. Available: https://www.gov.uk/government/statistical-data-sets/road-traffic-statistics-tra#traffic-volume-in-miles-tra01. [Accessed 12 April 2021].
[2] UK Government, "Vehicle Statistics: All Vehicles (VEH0104)," 9 December 2020. [Online]. Available: https://www.gov.uk/government/statistical-data-sets/all-vehicles-veh01. [Accessed 16 February 2021].
[3] G. Kacher, "Car Magazine," 23 March 2021. [Online]. Available: https://www.carmagazine.co.uk/car-reviews/volkswagen/id4-suv/. [Accessed 12 April 2021].
[4] Electric Vehicle Database, 2021. [Online]. Available: https://ev-database.uk. [Accessed 12 April 2021].
[5] ReFLEX Orkney, "Dashboard," 2021. [Online]. Available: https://dashboard.reflexorkney.co.uk/admin/dashboard. [Accessed 1 May 2021].
[6] Orkney Islands Council, "Orkney's Electric Vehicle Infrastructure Strategy," May 2014. [Online]. Available: https://www.orkney.gov.uk/Files/Transport/Electric/Orkneys_Electric_Vehicle_Infrastructure_Strategy_Accessible.pdf. [Accessed 4 April 2021].
[7] C. Iclodean, B. Varga, N. Burnete, D. Cimerdean and B. Jurchiș, "Comparison of Different Battery Types for Electric Vehicles," in IOP: Materials Science and Engneering, Orlando, 2017.
[8] "Battery Aging in an Electric Vehicle (EV)," Battery University, 22 August 2020. [Online]. Available: https://batteryuniversity.com/learn/article/bu_1003a_battery_aging_in_an_electric_vehicle_ev. [Accessed 12 April 2021].
[9] UK Government, "Monthly Automatic Traffic Count," 12 April 2020. [Online]. Available: https://data.gov.uk/dataset/688a71fe-3189-4eb5-8a6d-18772cce8203/monthly-automatic-traffic-count-data. [Accessed 12 April 2021].
[10] UK Government, "Electric Chargepoint Analysis," 13 December 2018. [Online]. Available: https://www.gov.uk/government/collections/energy-and-environment-statistics. [Accessed 12 April 2021].