1. Introduction
EU legislation targets are to cut CO
2 emissions from cars by 37.5% by 2030 [
1]. Currently, the transport sector is a significant contributor to greenhouse gas emissions. An increase in the uptake of electric vehicles could contribute to the EU’s policy objective of reducing greenhouse gas emissions from transports. Globally, low-carbon and sustainable energy actions are already underway, including electric mobility (e-mobility) initiatives, aiming to boost the transition to low (and zero)-emission vehicles. Electric vehicles represent a promising solution that meets the environmental goals for global sustainable development in terms of reducing local air pollution and addressing climate change.
Stricter emission regulations, lower battery costs, widely available charging stations, and increasing consumer acceptance will create new and strong momentum for market penetration of electrified vehicles in the coming years. Without exception, the present technical and economic studies predict a progressive replacement of internal combustion engine vehicles with EVs in the years to come.
Today the market offers several types of EVs that may be classified according to their propulsion systems and energy sources, including battery electric vehicles (BEVs), hybrid electric vehicles (PHEVs), plug-in hybrid electric vehicles, and extended-range electric vehicles [
2,
3]. In the future, other solutions may be available, including adding a fuel cell range extender to electric vehicles [
4]; among other impacts, this approach might reduce the so-called range anxiety and affect vehicles owners’ behavior. EVs rely on plug-in electricity, requiring a home charging point. They take electricity from the distribution grid and store it in rechargeable batteries that power the electric motor. Therefore, an affordable charge infrastructure is essential for the widespread adoption of EVs [
5].
Several scientific works have been published, disseminating strategies and methodologies for analyzing and assessing the batteries’ behaviors [
6,
7]. The studies’ focus ranges from the maximization of the battery operation itself to the minimization of environmental impacts. They present significant results to minimize load peaks, flatten the load profile, and maximize the integration of renewables [
8,
9].
Several researchers have explored EV charging activities and their impacts on residential and distribution networks [
10,
11]. In addition, the impact of EV charging was validated in downtown Manhattan by assessing the effect on the distribution grid [
12].
At the regional level, the charging of EVs can significantly increase electricity loads, causing possible negative impacts on distribution networks (e.g., cables and distribution transformers), especially for high-power charging [
13]. The charging of residential EVs results in a significant increase in household electricity consumption that may exceed the maximum power supported by the distribution system itself. The situation can be worsened during times of high electricity utilization, such as peak hours or extreme days.
The distribution grid will have to carry out interventions and upgrades to manage the new and progressively increasing heavy energy load. To solve the technical constraints and understand how the network will withstand the increasing penetration of EVs, Mancini [
14] developed urban and rural grid models to highlight the differences between the impacts on high- and low-density networks.
Although the transition to EVs is inevitable, their massive penetration will undoubtedly impact energy system management. Forecasting energy consumption helps to prepare for appropriate supply. In the literature, one can find forecasting models [
15] that use five-year energy consumption data from a specific region and use the grey fractional model to analyze the next six years. Other forecasting methods have been studied, showing different requirements for raw data [
16,
17].
From technical and cybersecurity concerns to economic and social impacts, many issues have been addressed by several researchers, such as Ceballos Delgado [
18], Das [
19], and Jiang [
20]. Other studies have already considered the consequences of a high EV penetration into the electricity market [
21,
22] in terms of the additional electrical load and surges in demand during peak hours. Anastasiadis [
23] addressed the security of the distribution grids, while Khalid [
24] analyzed problems related to power quality and reliability. Some authors have presented methodologies to limit the maximum power extracted from the grid to recharge EVs [
25,
26]. However, in the future, the integration of vehicle-to-grid (V2G) technology and smart grid charging may help address grid congestion and maintain the reliability and security of the power supply [
27,
28].
EV sales growth is a reality all over the world [
29], driven by macroeconomic factors on which the development of battery technology and charging accessibility depend. At present, the purchase of an EV is not yet within everyone’s financial reach, due to factors such as the high initial cost, battery degradation, and inadequate charge infrastructure [
30]. Therefore, the evolution of EVs will largely depend on social and macroeconomic factors (including the rise of the global consumer middle class) and new mobility services such as car-sharing and e-hailing [
31]. Currently, public financial incentives, such as reduced road and vehicle acquisition taxes, still directly impact BEV sales [
32]. Norway is an example of the use of incentives aiming at massive electric vehicle adoption; the country has exempted BEVs from registration taxes since 1991 and from value-added tax since 2001; has waived tolls and ferry and parking fees for BEV owners since the late 1990s; and BEV drivers are allowed to use bus lanes and pay reduced company car taxes [
33]. In 2020, BEVs accounted for 51.6% and PHEVs for 22.9% of Norway’s passenger car sales [
34]. Despite incentives, Norway had excellent conditions to adopt electric vehicles—a wealthy population, cheap hydroelectric energy, and high home charging availability, which are prerequisites that are unlikely present in most countries [
33]. Today, Norway is dealing with more investment in public charging capacity, namely in regions with low EV density (raising charger placement issues).
Nevertheless, price reductions in further electric vehicles and business models such as car leases may enable people with no available capital to purchase electric vehicles. Additionally, the smart charging concept is worth mentioning, which refers to all intelligent technologies enabling a car to be charged at the best possible moment, thereby reducing the local grid congestion. In addition, residential smart charging could also smooth the integration of BEVs in the grid and could provide financial benefits to drivers, thereby reducing ownership costs [
32].
E-mobility has reached a point of no return. As more models become available and prices decrease, EV purchases will increase, reaching a broader range of the vehicle-owning population, which should encompass more than 10% of sales by 2025 and 20–30% of sales by 2030 [
35]. The current production forecast [
36] reveals that car producers are expected to manufacture more EVs in the EU than necessary to comply with the minimum requirements of the EU CO
2 emission reduction standards. The share of EVs in car production in 2025 will be around 22% if carmakers follow the current vehicle production forecast, which is higher than the average 15% EV sales share needed.
The EV market in Portugal is also evolving at a fast pace. In 2020, the total number of BEV passenger cars circulating was 36,882, while PHEVs reached 27,710 units; combined, PEV and BEV cars represented a little over 1% of the national car fleet [
37,
38,
39], which was over 5.5 million cars in 2020 (
Table 1).
Figure 1 displays the total number of BEV and PHEV passenger cars registered between 2015 and 2020 and their respective percentages relative to the total national fleet (including all types of cars).
Despite the short-term impacts of the COVID-19 pandemic, resulting in a severe decline in national total passenger car sales because of economic uncertainty and changing consumer priorities, BEV and PHEV sales kept increasing, reaching a combined 13.5% of total passenger sales in 2020 [
37], as seen in
Figure 2. Moreover, continued growth is expected to be sustained throughout the 2020s [
40].
There must be a huge investment in charging infrastructure, without which the de-carbonization of transportation via electrification will be at stake. Additionally, distribution grids must be strengthened to cope with the expected energy demands from EV owners, especially considering the ambitious goal of achieving 20% e-mobility in 2030 established by the Portuguese government [
41].
As mentioned by Awadallah and colleagues [
42], every grid is a special case requiring an autonomous study to explore the issues and limits of EV charging loads. This paper aims to forecast the
BEV segment development toward the 2030 horizon and its effect on the distribution power grid for an area comprising 20 municipalities in Northern Portugal. The case describes three scenarios that consider different goals and energy consumption levels, relying on three popular EV models in the country, namely the Nissan Leaf, Tesla Model 3, and Renault Zoe. The impacts of the growing EV fleet on the distribution network are assessed, namely the extent to which the available grid power for charging copes with the load demand increases during peak and off-peak hours. The distribution network in this case study is analyzed according to its technical characteristics, constitution, and substation building type. The results are discussed to identify possible measures to address the impacts mentioned above and conclude if and when the local power grid operator should invest in the coming years to be prepared for such impacts.
3. Monte Carlo Computational Simulation
At this point, one could question the likelihood of the occurrence of the three scenarios. The national goals set for the 2030 horizon in [
41], which led to scenario 3, result from the government commitment towards achieving carbon neutrality in 2050, in line with EU targets. Therefore, one could expect the government to create measures to encourage grid operators to invest in increasing the power infrastructure capacity and consumers to shift their preferences to EVs. As such, EV sales will probably rise, and as more recharging stations become available, BEVs sales will be boosted. Accordingly, scenario 3 may be the most likely; it would be prudent to take it seriously because it points to dramatic impacts. Moreover, power demands due to EV sales could increase even further. As mentioned previously [
36], carmakers are already planning for sales beyond the EU’s regulatory CO
2 compliance for 2025 and 2030, as they foresee a real market-driven demand for electric cars. As such, the national electric vehicle fleet should experience growth beyond the forecast in scenario 3 if the Portuguese market follows that trend. In the absence of known estimates concerning more severe scenarios, one can only acknowledge the likely acceleration in EV adoption compared to scenario 3 and consider the BEV sales as a probabilistic variable; then, one can use Monte Carlo computational numerical methods to forecast the impact of BEVs on the power grid, incorporating stochastic variability in the deterministic base case in scenario 3.
As mentioned in [
36], EV production may reach 22% of total passenger car production in 2025, higher than the 15% of sales needed to comply with the EU targets, which means sales could be around 46% higher than expected. We will start from a three estimated points approach, defining the sales under scenario 3 as the most likely, the sales under scenario 2 as optimistic, and a new sequence of yearly sales 46% higher than in scenario 3 sales as pessimistic. To perform the Monte Carlo simulation analysis, the BEV sales from 2022 to 2030 will be modeled as a beta-Pert distribution, using the pessimistic, most likely, and pessimistic sales as parameters (sales in 2021 will remain the same as before). A 10,000 trial simulation shows that the aggregate impact means for the peak and off-peak hours are not very different from the base case scenario 3. However, it now reveals the probability of that impact being negative, which is valuable information (
Table 8, in bold).
As an example,
Figure 7 depicts the simulation for 2027 during peak hours; the red area of the curve translates into a 34.7% probability of negative impact.
In the simulation base case (scenario 3), the aggregate impacts during peak hours are negative only from 2028 to 2030; now, the simulation reveals that there is a 0.3% and 34.7% likelihood that those impacts will occur by 2026 and 2027, respectively. Similarly, the aggregate impacts during off-peak hours are negative only in 2029 and 2030; now, there is a probability that they will also happen in 2028. The simulation confirms scenario 3′s expectations and shows that there is a risk of failing to cope with demand earlier than expected.
4. Discussion and Conclusions
This case study addressed the growing BEV passenger car fleet in 20 municipalities of Northern Portugal and how the required power for recharging batteries will impact the local power distribution grid. The case was first analyzed under three scenarios. Firstly, assumptions were established concerning demographics, representative entities for a BEV, its power consumption, and daily distance covered (weighted average of long and short routes), and public information was gathered to describe the installed power grid capacity within the considered municipalities and the national EV sales and fleet. Then, each scenario was specified with further assumptions. In brief, scenario 1 assumed the goal of achieving BEV sales equaling one-third of the total national sales in 2030. In scenario 2, the goal is maintaining the recently registered sales growth from 2019 to 2020 during the 2021–2030 period. In scenario 3, the goal is for the national BEV passenger car fleet to reach 20% of the national total. The number of BEVs in the region was estimated as a percentage of the national fleet (calculated as the proportion of residents to the national population), while the required power by each BEV was 10.35 kVA. Finally, the impact of the BEV fleet on the power distribution grid was estimated as the difference between available power and the required energy for both peak and off-peak hours. In all scenarios, some municipalities were unable to cope with the demand for recharging batteries. The aggregated demand in scenarios 1 and 2 was satisfied by the installed capacity; however, in scenario 3, the grid could not satisfy the demand from 2028 to 2030 during peak hours and from 2029 to 2030 during off-peak hours. Another forecast was carried out, acknowledging the possible acceleration of EV sales at a rate 46% higher than expected (keeping in mind EU targets). In that case, the authors decided to perform a Monte Carlo computational simulation to predict the power demands, incorporating uncertainty in the deterministic base case in scenario 3, which impacted the aggregate demand, which although not far from the base case showed a significant probability of being negative earlier than expected. This information is valuable for the grid operators because it provides a measure of the risk of not meeting BEV demand and underpins the need to consider timely expansion investments of the power grid.
The study’s deterministic and stochastic modeling of BEV fleet impacts on the power grid shows that the network runs out of its feeding capacity if BEV production increases until the end of the decade. This approach could be easily replicated in other regions, provided the parameters are calibrated to reflect differences in the considered variables. However, one should note several aspects of the case study assumptions that could significantly alter the model and its outputs. Firstly, the representative BEV was characterized based on three models only. The availability of new affordable BEVs will soon change the current scenario. Additionally, one can anticipate that carmakers will invest in improving all EV characteristics, including weight and efficiency. Therefore, the representative model should be adjusted accordingly. Secondly, the required power for recharging a BEV was estimated based on the daily distance covered by a vehicle and the characteristics of the routes. In this case, a representative route was defined based on long- and short-distance paths. Other routes could be considered, which might create alternative energy requirements. Thirdly, our approach estimated the BEV fleet as a proportion of the local population to the national population. This assumption could be refined, as the expected population growth for the region may be somehow evolve differently from the country’s population growth. Additionally, the local residents’ average purchasing power may not coincide with that of the national residents. Another important remark is that the forecasts described in the case study estimated the ability of the local power grid to attend to the BEV fleet demands as a whole; that is, the model analyzed whether the grid could cope with all demands during peak and off-peak hours. Eventually, the grid could feed all BEVs if the consumers comply with controlled recharging, splitting demand between both periods. Although operators may encourage charging during off-peak hours, it is not guaranteed that consumers will cooperate; as such, we opted for the worst-case scenario. However, should there be any reason to believe that splitting could be enforced, a new study should analyze the impacts of controlled consumer behavior. Finally, other BEV sales and fleet forecasting assumptions do not take into consideration the idea that possibly alternative technologies may make an impact soon (e.g., hydrogen cars), while PHEVs could still have opportunity for growth if carmakers decide to improve their technology and weight, which would change assumptions about sales and market shares.
The replication of the case study approach in other regional networks may highlight congestion issues. To tackle such situations, distribution operators must strengthen their infrastructure. In addition, there are various additional technical interventions to consider: the current conductors’ replacement with a larger cross-section to withstand the thermal limits; the insertion of more conductors in parallel to decongest the overloaded cables; and the transformer power reinforcement, which is the most crucial upstream action. Additionally, the distribution grid considered in this study comprises consumer substations of different building types (PMS, HCS, and LCS). The BEV fleet growth will cause impacts in terms of voltage drops; some are better prepared to meet increased demand than others. In this regard, major physical interventions may be necessary, as is the case with building restructuring. Another approach is to explore the dynamic line rating (DLR) approach, whereby the power system has thermally sensitive assets such as lines and transformers, and there is a growing trend to use the capacity of those assets dynamically under varying operating conditions [
53]. A good solution to lighten the consequences of BEV demand increases is micro-production. The self-production of photovoltaic electricity is becoming crucial. Charging a BEV with electricity generated by photovoltaic systems should become a worthwhile option. The energy from a building’s own roof is cost-effective and has net-zero emissions. Providing easy home and workplace charging should be a priority. Although not within the scope of this study, one should mention the negative impact that the integration on the grid of other electric vehicles may cause, namely trucks and bus fleets [
28]. This perspective calls for the adoption of smart charging to address the expected grid congestion and maintain the reliability and security of the power supply. Finally, storage systems based on the second use of discarded electric vehicle batteries have been identified as cost-efficient and sustainable alternatives to first-use battery storage systems [
54]. In addition, EV second-life battery storage systems may prove responsive, efficient, and scalable [
55]; they could contribute to additional buffer capacity for the electrical grids.
There is little doubt that EVs are here to stay. Consumers are increasingly more inclined to consider EVs. As prices decrease and governments offer financial incentives such as tax reductions and exemptions for electric vehicles, the shift towards electric mobility will increase. Power grid operators must be aware of this process, anticipate infrastructure investments, and manage BEV recharging to cope with this growing demand. Charging infrastructure needs to be effectively deployed in line with the growing EV uptake at all levels. This study intended to provide an original and feasible approach to analyze the impacts of BEV passenger fleet growth on the power grid until 2030. It could be adjusted to reflect improved assumptions and contextual changes and could helpful in studying other grids beyond the one considered in the case study.