To access the overall environmental impact that EVs have on the electricity grid certain factors are taken into account.
(i) To investigate the energy demands that an increased number of electric vehicles will apply to the current electricity system.
(ii) To evaluate the environmental impacts the research focuses on the carbon emissions produced by these vehicles, currently the UK has plans in place to reduce the CO2 emissions by 45% by 2020 (Sithole et al., 2016). Petrol and diesel cars will gradually be phased out by 2030.
The method used in this work is accessed the success of large-scale deployment of EVs into the UK.
3.1 Assessment of the impact of EVs on energy demand
A scenario-based simulation tool is used to evaluate the impact of EVs in the future depending on the market penetration of the vehicles. Once the percentage of EVs has been predicted in the future in terms of the entire car fleet it is important to investigate detailed information about the car fleet itself. There are a number of factors that need to be explored including:
i) Total predicted number of cars in the ‘car fleet’.
ii) Energy required recharging the ‘car fleet’.
iii) Composition of the ‘car fleet’.
To gain an idea of the demand that EVs will have on the electricity grid this research investigates at the yearly requirement of electricity that EVs will require at different market penetration levels. This scenario is based on the fact that all EVs will only be charged when they needed. The total number of charges daily can be calculated by dividing the range of the vehicle by the total miles travelled daily; this work assumes that EVs daily mileage for commuting trips is in the 20 miles range.
By looking at the daily energy demand in more detail it is possible to assess the impact that EVs will have on the electricity grid. Information of the daily energy demand will be compared to the demand placed on the grid by changing levels of market penetration.
a) The number of charges daily is multiplied by the number of vehicles for the total number of daily charges needed for the entire fleet.
b) By multiplying the value in (a) by the battery capacity and dividing by the battery efficiency of 90% it is possible to gain a value of the total electrical energy required.
c) A yearly total of electricity required by the fleet can be calculated by multiplying the daily energy required by 365 days.
Figure 1 shows the predicted energy consumption in the UK in 2030. This will act as a comparison to evaluate the impact on electricity demand due to EVs.
3.2 Assessment of the impact of EVs on the energy demand
When assessing the potential impact of EVs on the electrical grid and in particular the entire electric consumption a number of key factors have to be considered.
- The core technical features for the available cars need to be evaluated; from a short to medium term.
- The market penetration of the fleet of vehicles available needs to be estimated in terms of future evolution.
A study by Harris (2009) investigating the impact of the energy requirements of an increased number of EVs on the UK electricity grid in short and medium term. It is found that the grid capacity should be adequate for a 10% market penetration of EVs. However, as EVs are still in early stages of production it is hard to estimate future trends regarding the vehicles, market response will affect the vehicles development as well as technological advances. Harris (2009) also stated that local network problems could be an issue depending on distribution network capacity and concentration of EVs.
The technical features of the EVs in the future will determine potential market penetration. Factors that need to be considered are:
- the battery capacity of EVs and;
- the range or distance they can travel.
- their energy consumption per unit of distance covered.
All of these elements influence the type of commuter that will drive these vehicles. Currently the range of EVs regards as being particularly small; some vehicles barely reaching 100 miles (Wu et al., 2015) . This means that the vehicles therefore need to be recharged more frequently and this process currently requires several hours depending on the energy available. Putrus et al., (2009) claim that slow charging from a single phase takes around 6 hours. Majority of the people that do not need to travel long distances are suited to these vehicles; satisfying their need to help the environment is also a factor to purchasing EVs. Due to the cars small range of travel this makes them very suitable for urban use. However large urban cities are highly energy consuming areas, this means they may substantially suffer from the electrical energy demand of these vehicles. The UK has been chosen as a case study because of its urbanised areas and potential market penetration in the future for EVs.
Table 1. Available EVs
Manufactures
|
Type of EVs
|
Battery Capacity (KWh)
|
Time to Charge (Hours)
|
Distance Travel (Miles)
|
Consumption (KWh/100 Miles)
|
Nissan
|
LEAF
|
24
|
5
|
124
|
19.35
|
Mitsubishi
|
Outlander
|
12
|
5
|
34
|
35.29
|
BMW
|
i3
|
22
|
5
|
80
|
27.5
|
Renault
|
Zoe
|
22
|
5
|
149
|
14.77
|
Tesla
|
Model S
|
85
|
5
|
265
|
32.08
|
Kia
|
Soul
|
27
|
5
|
132
|
20.45
|
Volkswagen
|
E-UP
|
18.7
|
5
|
93
|
20.11
|
Ford
|
Focus-Electric
|
23
|
5
|
76
|
30.26
|
Audi
|
E-Tron
|
9
|
5
|
31
|
29.03
|
Table 1 shows a collection of EVs available in the UK during this research investigation. Table 2 shows a summarised classification of vehicles, the vehicles have been clustered into specialised groups depending on the capacity of the battery. The vehicle categories chosen for this study are small, medium and large. Table 2 includes the expected recharging times for the vehicles. Recharging time is very important as it helps to estimate the energy required by all of the EVs. The recharging times vary for each vehicle; for this study the investigation have considered an average recharging time of six hours. This time is expected to decrease due to technological developments.
Table 2. Simplified groups of EVs
Segment
|
Battery Capacity (KWh)
|
Time to Charge (Hours)
|
Distance Travel (Miles)
|
Consumption (KWh/100 Miles)
|
|
|
Domestic
|
Fast
|
|
|
Small
|
15
|
6
|
1
|
50
|
30
|
Medium
|
25
|
6
|
1
|
80
|
31.25
|
Large
|
35
|
6
|
1
|
110
|
31.81
|
The recharging power for each individual vehicle of a car fleet has been calculated as shown in Table 3. The power required to the grid is dependent on the type of charging available. Domestic charging requires a longer time to recharge but less electrical energy is needed from the grid to fully charge a vehicle. The fast charging option requires a considerably larger amount of energy from the electricity grid because it charges in a substantially shorter time.
Table 3. Estimated power required to recharge 1 vehicle
EVs
|
Electricity Required by Grid (KW)
|
|
Domestic Charging
|
Fast Charging
|
Small
|
2.78
|
33.33
|
Medium
|
4.63
|
55.56
|
Large
|
6.48
|
77.78
|
Furthermore, the li-lon battery efficiency needs to be taken into account of in order to understand how much electrical energy is required to the distribution grid. For this study a battery efficiency of 90% has been considered (Richardson et al., 2012). The battery efficiency discharge phase needs to be considered when looking at the range of EVs.
The recharging power to recharge each vehicle is determined by equation (1):
Power required by grid to recharge = Capacity x Time x 0.9 …………(1)
A PHEV is a hybrid vehicle with rechargeable batteries by connecting to the grid and has an internal combustion engine that can be activated when the batteries need recharging [40]. PHEVs offer the range of existing hybrid vehicles but also offer potential cost savings to ensure the energy benefits of fully electric vehicles.
It is critical to note that this study does not include the impacts of PHEVs on the electricity grid. The study considers all of the typologies of electric vehicles as one commodity when looking at the future of the electric car fleet. This investigation includes PHEVs and fully battery operated vehicles as one due to the type of trips that are considered. Since EVs have a limited range, the cars in this study are considered to be driven in short distances mainly for working purposes. As the vehicles would not be travelling excessive distances the internal combustion engine of the hybrid vehicles would not be required when making daily trips. Therefore the vehicles will operate in a sense as fully electric vehicles and will require the same energy. Consequently the same category will be considered when looking at market penetration of these EVs. .
A huge uncertainty of this study is the potential market penetration of EVs in the UK. It is important to understand the amount of EVs that will be in the UK in the future to gain an indication of their impact on the electrical grid. From the literature reviews, it has become clear that this research has already undertaken on the growth of PHEVs. The development of fully battery operated vehicles is predicted to be slower than PHEVs; reasons for this inclusion that there currently are more PHEVs on the market than EVs. However these factors become irrelevant in this study as this investigation assumes that they are as one entity. Many degrees of freedom of the uncertainty of the vehicles evolution have a resultant impact of projecting the progression of EVs in the future. This study examines the market penetration of EVs from 2014-2030. The model created develops a scenario where in 2030 there will be a different percentage of electric cars depending on the success of the vehicles penetration into the market.
As this work investigates the impact on the electricity grid from the growth of EVs in the future, Transport Statistics Great Britain (2020) contains records of the number of registered cars in the UK dating from 1970-2015. From this information it is possible to predict a trend for the amount of cars in the future as illustrated in Figure 2. Figure 2 shows the real number of cars and the estimated number up to 2030. Incorporating the predicted number of cars in the future and using the three market penetration scenarios already stated it is possible to gain an estimate of the market share of EVs in the UK. It is important to note that the amount of cars predicted in the future is only an estimate.
This study focuses on the impact of EVs on the distribution grid it is important to consider the technical information about the future ‘car fleet’. Electric cars have different battery capacities means different energy values are required by the electricity grid. Table 2 shows the three categories of electric fleet; small, medium and large. The composition of the vehicle fleet needs to be considered when investigating the total energy requirement of the EV fleet to the electric grid of the UK. By taking consideration of the new registrations by vehicle segment, it is possible to use the configuration specified in Table 4 to predict the amount of energy required by a future car fleet. To find out the total number of cars from each category the total number of cars predicted in that year is multiplied by the percentage stated in Table 4.
Table 4. Composition of EVs
Vehicles by Segment
|
Percentage (%) of Electric Car Fleet
|
Small
|
35
|
Medium
|
44
|
Large
|
21
|
To find out the impact that the vehicles will have on the electric supply system it is important to have comprehensive information about the system. Table 4 states the predicted energy required to fully charge a vehicle. The energy required to recharge each vehicle type can be determined by equation 2. The calculation used in the study assumes that each vehicle in the system in fully charged once a day.
Energy = Battery capacity / (Battery recharging time x Battery efficiency) ……… (2)
3.3 Assessment of the impact electric vehicles will have of carbon emissions
To assess the impact of EVs on carbon emissions by using data on the energy mix in the UK. As explained in the literature review EVs claim to have zero emissions but carbon is still emitted into the atmosphere as a result of electricity production. Therefore, to evaluate the impact of large deployment of EVs, the way in which electricity is produced will need to be investigated. Consequently, this research work will look at datasets that predict the way the UKs electricity production in the future. This part of the research work focuses on evaluating the impact EVs on the electricity grid in terms of reducing carbon emissions by considering different market penetrations of EVs. The factors that need to be taken account of in the prediction are:
- Different market penetration levels of EVs will be considered ranging from 5% to 30%.
- Different carbon emission factors for the ‘normal’ vehicle fleet will be considered.
- To calculate the carbon emissions produced by electricity generation a carbon emission factor needs to be used. This factor remains constant throughout the model. It converts KWh of electricity to KgCO2 per mile travelled per car.
- The prediction uses a constant driving range of 20 miles.
In order to find out the impact of EVs on carbon emissions information regarding the UKs energy mix is necessary. The energy used to power the cars has been generated from a mix of production technologies which will produce a corresponding quantity of emissions. The energy mix contains information about what fuels are used to produce electricity and the percentage of usage.
- Electricity carbon Factor
This work uses an electricity carbon factor to predict the carbon emissions produced from generating the electricity used to power the EVs. The electricity carbon factor converts the electricity needed to power the car fleet in KWh to carbon emissions produced (KgCO2). For this work a carbon emission of 0.4585 was used which corresponds with the 2015 electricity carbon emission factor (International Electricity Factors., 2018). It is important to note that this carbon emission factor is an average and changes from year to year. Therefore this research predicts results that show an improved reduction of CO2 emissions as a result of an increased number of EVs in the future.
To access the impact of carbon emissions this project uses a driving range of 20 miles, this is because the study assumes that EVs will be used for commuting purposes. This driving range used is equivalent to the driving range used to access the impact of EVs on the electricity grid.
The carbon emissions per kilometre of travel are converted to find the overall CO2 impact. This study evaluates from the aspect that the gCO2 per kilometre per car will only improve.