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Abstract
This paper focuses on the development of electric vehicle (EV) charging infrastructure in the UK, which is a vital part of the delivering ultra-low-emission vehicle (ULEV) and will transition into low emission energy systems in the near future. Following a brief introduction to global landscape of EV and its infrastructure, this paper presents the EV development in the UK. It then unveils the government policy in recent years, charging equipment protocols or standards, and existing EV charging facilities. Circuit topologies of charging infrastructure are reviewed. Next, three important factors to be considered in a typical site, i.e., design, location and cost, are discussed in detail. Furthermore, the management and operation of charging infrastructure including different types of business models are summarized. Last but not least, challenges and future trends are discussed.
CLIMATE change poses a great challenge to the sustainable development of human civilization. Governments around the world are working to reduce carbon emissions, of which road transport tend to account for a significant proportion. As a result, vehicle emission targets have been put in place in many countries. Electric vehicles (EVs) featured as environmentally friendly have thus got extensive attention in recent years [1]-[3]. According to [
Meanwhile, with the rapid development of EV, its supply equipment or charging infrastructure is essential. Apart from the technological innovation of EV, effective charging infrastructure plays a fundamental role in supporting the wider adoption of EV. By 2017, it has been estimated that there were about 430 thousand public chargers globally [
In the UK, the government has aggressive emission targets by 2030 and 2050. It is convinced that the majority of greenhouse gas emission is contributed by transport [
The UK government initially published an ultra-low emission vehicle (ULEV) strategy to encourage the growth in the ULEV market in 2009. The ULEVs are the vehicles that emit less than 75 g of CO2 per kilometer travelled, the vast majority of which are hybrid electric or pure electric. A strategy called “Driving the Future Today” was published in September 2013 and committed to cutting carbon emissions from transport, aiming at zero emission for nearly all cars and vans by 2050. The key elements of the proposed package for supporting ULEVs during 2015-2020 were set out in the following year [
The government has continuously published some grant schemes to incentivize the development of EVs as well. The grant for plug-in cars and vans was launched in 2011 and the grant structure has reformed since March 2016 [
For electric buses and taxis, the grant schemes were initially announced in April 2014, and the details of the scheme were published in March 2015 [
Furthermore, both private and business users of ULEVs receive a number of tax benefits ranging from fuel duty, vehicle excise duty (VED) and value added tax (VAT) that are applicable to all ULEV users to the taxation of company cars (CCT) and benefit charges for business users only. For example, regarding VAT, the electricity used to recharge a plug-in vehicle at home attracts only 5% level of VAT, much lower than road fuels (20%) [
New ULEV registrations and their percentage of all new registrations are shown in
Fig. 1 New ULEV registrations in the UK from 2011 to 2017.
In addition to making EV more affordable, the effective charging infrastructure network is another fundamental part to enable further promotion and wider use of EVs across the country. The government incentives and technical standards of the charging infrastructure are discussed below.
The development of EV infrastructure has been encouraged since 2009 [
According to the government response on the proposed “Directive” in September 2017, the government will publish National Policy Framework (NPF) to present information on the current quantity, spread and reach of alternative fuels infrastructure across the UK (e.g. EV charging points) and outline the future development of the infrastructure, and how these levels of infrastructure are likely to be achieved. Also, the national legislation imposing certain requirements on infrastructure operators will also be introduced.
A series of grant schemes have continuously sprung up since 2010. The government set up the plugged-in places (PIPs) scheme in 2010 to match funding for local business and public sector consortia to build their own electric charging points [
The EV home-charge scheme (EVHS) provides a grant of up to 75% towards the cost of installing charging points at domestic properties. The workplace charging scheme (WCS) is a voucher-based scheme that provides support for eligible businesses, charities and public sector organizations. For each application, the funding is limited to £300 for each socket up to a maximum of 20 across all sites. The on-street residential charge-point scheme (ORCS) provides grant funding of 75% of the capital costs up to a maximum of £7500 for local authorities.
Specifically, these grant schemes refer to the guidance for consumers or applicants, installers and manufactures. Minimum technical specification for manufacturers of charging point units are particularly pointed out. Authorized installers, approved charge-point models and eligible vehicles are also listed in the schemes.
Furthermore, the government has pledged £80 million to improve the charging infrastructure for EV owners and £30 million to study, design and develop revolutionary vehicle to grid (V2G) technologies [
Apart from some basic standards like British Standard BS 1363-13 (a plugs socket-outlets adaptors and connection units) and British Standard BS EN 60309-2 (plugs, socket-outlets and couplers for industrial purposes) for generally domestic and industrial plug and socket system [
There are four different types of EV charging system referred to as “modes” [
Tesla has installed bespoke chargers with an adapted type 2 tethered plug that can provide DC energy up to 145 kW across the UK since 2015. This type of charger belongs to DC rapid here.
Three typical categories of charging speed exist in practice [
Fig. 2 AC connector type 2.
Fig. 3 DC connector. (a) CHAdeMO. (b) Combo 2 or CCS.
As is shown in
For manufacturers of EV charging equipment who seek authorization from OLEV, they should apply to OLEV first by filling an application form. Their products would become authorized in the EVHS and WCS if the form provides enough evidence that the equipment is compliant with the corresponding standards set out in the minimum technical specification.
The number of EV charging points has been increasing steadily in recent years from a few hundred in 2011 to 4967 charging locations with 14231 connectors by 2017 [
Fig. 4 Charging points by type from 2011 to 2017.
The numbers of rapid charging connectors by type during 2011 and 2016 are shown in
Fig. 5 Rapid charging connectors by type from 2011 to 2016.
The profile of charging points/connectors (by Nov. 2019) in each of the UK regions is shown in
Fig. 6 Profile of charging connectors (total 16464).
In May 2018, it is announced that National Grid has teamed up with Pivot Power to invest £1.6 billion in building grid-scale 50 MW batteries and rapid EV charging docks across the UK [
In a typical EV charging point project, the following three factors are of the most importance, namely design, location and cost.
Charging points are usually floor-mounted or wall-mounted. The main components of such charging point mounted on the floor or on the wall are shown in
Fig. 7 On-street restricted access charging points (floor-mounted).
Fig. 8 Off-street open access charging points (wall-mounted).
Globally, several topologies for charging stations are proposed which can be categorized into mainly two most popular types, namely back-to-back AC/DC converters [34]-[36], and transfomerless charging stations [37]-[39]. The back-to-back AC/DC converters consist of a front-end AC/DC converter interfaced with the network via a transformer, whilst the transformerless ones usually decrease the current by connecting the charging station directly to a medium-voltage level. All these topologies could perform bi-directional charging, which could be integrated with battery energy storage system and to provide grid support services. The differences mainly lead towards power density, modularity and reliability. For urban area with limited spaces, a transformerless topology with higher power density may be the better option. For shopping centers and motorway where the infrastructure requires modularity and less control, back-to-back AC/DC converter may be the choice. AC/DC and /DC/DC charging station with high modularity and simpler control would be a suitable choice for charging stations in shopping centers or alongside highways.
From the perspective of charging, it can be further categorized into conductive and inductive charging technologies [
EVs can be charged using different types of charging points. But due to different locations, different designs need to be adapted. There are mainly four types of charging point locations namely domestic, workplace, public car park and on-street parking.
More than 60% of UK domestic dwellings have garage or other types of off-street parking [
Fig. 9 Weekly demand profile averaged over a whole year at distribution network operator (DNO) licensed area level for residential charging for an average EV.
From the perspective of distribution network operator, it shows a similar evening peak demand across all areas. London is noticeably lower for the evening peak hours possibly due to smaller share of cars used for commuting and lower average commuting distance compared to the rest of the UK. At weekends, the influence from commuters is much lower. If EV uptake becomes norm across the UK and home charging is still dominating, distribution network reinforcement needs to take place to mitigate expected spikes in demand from EV charging.
Existing EV owners mostly rely on home recharging supported by workplace charging to commute [
With regard to charging behavior,
Fig. 10 Weekly demand profile averaged over a whole year at DNO licensed area level for work charging for an average EV.
Home and workplace charging can be further supplemented by the expanding public EV charging network. This includes leisure centers and sports facilities, retail outlets, community facilities, parks and other green spaces, education facilities and motorway services stations. Public car parks are either owned by local councils or private businesses. They are usually enforced and users pay for parking by either pay and display, pay on foot, pay by phone or automatic number plate recognition (ANPR) managed. Most of the public car parks are found in town or city centers for customers or visitors, where parking bays are limited and cost can be at a premium. Signing parking bays to EVs may only need to be justified against the business model and popularity of EVs in the local area. In addition, parking legislation needs to be reviewed to ensure that EV parking spaces are not abused by both non-EV owners and EV owners who park with little charging or completely without charging. Motorists often park at these locations for a limited time depending on their purpose of visit. Therefore, slow or standard charging may not be very helpful for these applications. In commercial applications and public car parks, charging points may operate at higher rates with rapid AC (mode 3) or DC (mode 4) charging to reduce charging times accordingly. Therefore, power supply could be a major challenge to these locations if there is no existing grid connection other than light circuits. In the meantime, charging points can be floor-mounted or wall-mounted in external car parks. On the other hand, they are usually wall-mounted in internal car parks including multi-story ones [
Comparing the charging behavior for public with residential and workplace, according to
Fig. 11 Weekly demand profile averaged over full year at DNO licensed area level for slow/fast public charging for an average EV.
On-street parking locations are usually owned and operated by local or transport authorities. Similar to public car parks, as the sites are usually limited for availability and are often located in town or city centers, parking at these locations will generally be at a premium. Also, the maximum permitted stay for these locations lasts usually 3-4 hours during the day, in which time users would usually expect to achieve at least 80% of the full charging of their vehicles [
Typical cost of a charging point can be split into three parts: capital cost, installation cost and operation cost. The cost of purchasing and installing charging points can be credited to several factors. The most important factor is whether it is restricted-access or open-access [
According to [
Installation cost is the most variable in a charging point project. Without detailed information of the site, it is impossible to estimate the installation cost. It is affected by too many factors including but not limited to the charging point model, location and power supply. In practice, the installation could cost as much as the charging point itself [
Generally, operation costs include maintenance, servicing, warranties, data services and insurance [
Charging points can either be operated as a standalone device or connected to a back-end system via network connection. Most of the public car parks need to implement access control and billing function for their charging points. Without a live network connection, standalone charging point will have very limited functionality, especially when the offline user authentication and payment system is involved. Moreover, there is no remote observability over standalone charging points to monitor, diagnose or upgrade the chargers. Therefore, public car park operators would rather prefer connected charging points considering advantages brought by the connectivity over the cost of running such service [
There are mainly two types of shared charging point operation model, open-access or restricted-access [
Fig. 12 EV charging point communication schematic.
At the moment, electricity cost to charge EVs at home are roughly £225 per year based on an estimated annual mileage of 7500, which is equal to £0.03 per mile [
For workplace charging, it is common for employer to provide free charging to staffs and visitors. Similarly for public car parks, many of them are often free of charge as well to attract customers to visit their business [72]-[74]. At current stage, compared to publicity, the financial proposition is not very attractive to business owners. They are more than happy to absorb the charging cost. Considering the average hourly cost of £0.70 to the business owner, it is hardly a bank-busting amount while the customers will be shopping in the meantime [
Some charging point network operator runs their scheme on a subscription basis which charges a monthly membership fees with or without additional charges. POLAR Plus, part of POLAR charging network operated by Chargemaster, is one of the biggest charging point network operators in the UK, which has more than 2000 charging points with around 4000 connectors. Members pay £7.85 per month plus additional 10.8 pennies per kWh per charge where applicable. Yet the majority of their charging points are free. It is also introduced as membership fee, connection charges, license fee, etc.
However, the Government has recently proposed the Automated and EVs Bill [
PAYG allows charging point owners or network operators to bill EV users based on the energy delivered during charging events via instant or regular payments. It simplifies the EV charging costs for customers. In a survey done in [
The growing amount of EVs will drive the total demand and peak demand higher. As a result, the overall reliability of system might be compromised and additional capacity of generation is required. Also, the grid must have the ability to deliver necessary electricity for EV charging even under transmission congestion. Besides, at distribution level where EVs are particularly prevalent, the grid should accommodate the huge spikes [82]-[86]. Reference [
Larger EV batteries require faster charging technology to enable long mileage whilst maintaining reasonable charging time. In 2017, several fast charging standardization bodies released new descriptions or protocols to charge EV at up to 200 kW, including China Electricity Council, CHAdeMO and CharIN. Even if some high-power chargers are installed for demonstration in pilot projects, there are no EVs that can charge at the full-rated power yet. CHAdeMO has published their protocol up to 200 kW. A draft protocol CHAdeMO 2.0 allowing charging rate up to 400 kW will be published in 2018 [
The availability of convenient charging plays a key role in alleviating range anxiety for long-distance trips and promoting the wide adoption of EVs. Long-term allocation of charging infrastructures within an entire region decides the numbers, sizes and locations of infrastructures to meet the EV charging requirements, which is a complex optimization problem [90]-[92]. The charging demand in the future should be estimated considering the increase of EV numbers and their charging behaviors. Some of the factors, such as the types and models, the cumulative impacts on the grid, the geographic location, and the management of these charging infrastructures, should be paid attention to as well [
Wireless charging system has been widely discussed for high-power applications, especially for stationary EVs. Compared with plug-in system, wireless charging is advantageous in user friendliness, simplicity and reliability. Currently, wireless charging system can be categorized as inductive power transfer, capacitive wireless power transfer, magnetic gear wireless power transfer and resonant inductive power transfer [94]-[98]. Meanwhile, wireless charging in motion has been sought out [
It is the intelligent charging of EVs, where charging behavior can be shifted based on grid loads, renewable generation and in accordance to the need of EV owners [103]-[106]. EV owners can get monetary benefits offered by the utility if they participate in a program that allows controlled charging or responds to price signal during the periods when curtailment capacity is needed for the grid [
Electric Nation, one of the WPD’s innovation project, is one of the world’s largest trials. It covers more than 40 different makes and models of EVs, providing smart charging services to over 500 EV drivers. In
Fig. 13 Annual consumption of charger by battery capacity.
As shown in
Fig. 14 Flexibility by time of plug-in weekdays (verticle lines indicate range of flexibility).
An EV typically absorbs power from the electrical system, but it can also work as a distributed storage and release power back into the grid, which is known as V2G technology that can bring potential benefits to both EV owners and grid utility [113]-[116]. To further implement V2G, related technologies of facility manufacture, e.g., batteries in EVs and two-way inverters within infrastructures, the business mode for managing EV interaction with the grid, and the construction of smart grid with smart meters, should be put in place first to support the integration of EVs and power grid. It has been long discussed in literature to utilize smart EV charging technology to provide grid ancillary service to improve system stability and reliability [
In July 2017, the UK government launched a £20 million V2G competition, which has been further boosted to £30 million in early 2018 with more than 20 V2G projects involving manufacturers, infrastructure operators, energy suppliers and academia.
This paper introduced the development of EV infrastructures in the UK, including government strategy, standards, design, placement and cost. The successive governments have planned grants and incentives for infrastructure to encourage their growth. In addition, EV infrastructure management and operation have also been discussed to provide an insight towards a sustainable future-proof smart charging network.
The EV uptake in the UK will be substantially increased with the current strategy and roadmap from the government, with a potential projection of 10 million EVs by 2030 [
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