**2. Background**

Climate change is defined as the long-term alteration of temperature and weather patterns. There is robust evidence which indicates a consistent relationship between the cumulative greenhouse gas (GHG) emissions and projected increase in global temperature of between 1.5 ◦C and 2 ◦C above pre-industrial levels by the year 2100 [5]. Regional and local impacts of global warming are already seen as a consequence of the increase in GHG emissions. There is a strong concern that these impacts will worsen with stronger future climate change [6].

The Paris Agreement, which came into force in November 2016, commits developed and developing countries to keeping global warming below 2 ◦C and aspiring to a target of 1.5 ◦C [7]. According to the emissions gap report prepared by the United Nations Environment Programme (UNEP) in 2019, the total GHG emissions in 2018 amounted to 55.3 GtCO2e, of which 37.5 GtCO<sup>2</sup> was attributed to CO<sup>2</sup> emissions from the combustion of fossil fuels [8]. Hence, in tackling climate change, current efforts are primarily focused on reducing CO<sup>2</sup> and cover technologies and techniques that are deployed in four main sectors, power on the supply side and industry, transportation and buildings on the demand side. However, according to the recent UNEP report referred to above, even if all unconditional nationally determined contributions (NDCs) under the Paris Agreement were implemented, we are still on course for a 3.2 ◦C temperature rise. Further and immediate action is therefore required to combat climate change.

Of the four sectors mentioned, it is the transport sector that presents the greatest opportunity to respond. Taking the EU-27 as an example, transport—based on 2018 figures—accounts for almost a third of all CO<sup>2</sup> emissions, with road transport responsible for more than two-thirds of the transport related emissions [9,10]. Further, CO<sup>2</sup> emissions from road transport have increased by a factor of around 1.3 between the 1990 baseline and the most recent, 2019 figures. This compares to the decrease achieved in other sectors (see Figure 1). However, transport as a sector, which is highly reliant on fossil fuels, is perhaps also one of the most challenging to decarbonise [11].

perhaps also one of the most challenging to decarbonise [11].

for more than two-thirds of the transport related emissions [9,10]. Further, CO2 emissions from road transport have increased by a factor of around 1.3 between the 1990 baseline and the most recent, 2019 figures. This compares to the decrease achieved in other sectors (see Figure 1). However, transport as a sector, which is highly reliant on fossil fuels, is

**Figure 1.** Annual greenhouse gas emissions in the European Union from 1990 to 2019, by sector (in million metric tons of CO2-equivalent) [12]. **Figure 1.** Annual greenhouse gas emissions in the European Union from 1990 to 2019, by sector (in million metric tons of CO<sup>2</sup> -equivalent) [12].

The most attractive option for decarbonising the road transport sector is electrification, a market-ready technology alternative to the internal combustion engine [13]. Hence, as part of the UK commitment to net-zero GHG emissions by 2050 [14], the UK government has committed to ending "the sale of all new conventional petrol and diesel cars and vans", initially by 2040, but subsequently revised to 2035 and most recently to 2030 [15]. However, in order to achieve the net-zero goal, all road vehicles, including heavy-duty vehicles (HDVs), will need to be entirely decarbonised. Therefore, the UK Government has also announced its intention to consult on a similar phase-out to that planned for cars and vans but targeting diesel-powered heavy-goods vehicles [16]. The most attractive option for decarbonising the road transport sector is electrification, a market-ready technology alternative to the internal combustion engine [13]. Hence, as part of the UK commitment to net-zero GHG emissions by 2050 [14], the UK government has committed to ending "the sale of all new conventional petrol and diesel cars and vans", initially by 2040, but subsequently revised to 2035 and most recently to 2030 [15]. However, in order to achieve the net-zero goal, all road vehicles, including heavy-duty vehicles (HDVs), will need to be entirely decarbonised. Therefore, the UK Government has also announced its intention to consult on a similar phase-out to that planned for cars and vans but targeting diesel-powered heavy-goods vehicles [16].

The UK's ambitious plans to electrify its road transport fleet requires solutions that will reduce cost and drive up consumer confidence. Volume production of batteries, together with manufacturers targeting an increase in the energy density of batteries, has the potential to increase the driving range and at the same time provide a reduction in the cost of electric vehicles. The Automotive Council in the UK commissioned a roadmap on energy storage systems [17]. This roadmap targets a cost saving of around US\$80 per kWh between 2017 and 2035. During the same period, it also targets the energy density to double from 250 Wh kg−1 to 500 Wh kg−1. Further, the UK is pressing ahead with the rollout of charging infrastructure to support the electric vehicle user—both a rapid charging network to support users as they move about the UK, but also workplace and home charging solutions to support commuters and shoppers [18,19]. In addition, there is also the consideration of subsidies that either reduce cost or make available preferential access to road infrastructure including toll roads, city centres and parking [20]. However, these incentives are likely to prove unsustainable in the long term, requiring a focus on vehicle and The UK's ambitious plans to electrify its road transport fleet requires solutions that will reduce cost and drive up consumer confidence. Volume production of batteries, together with manufacturers targeting an increase in the energy density of batteries, has the potential to increase the driving range and at the same time provide a reduction in the cost of electric vehicles. The Automotive Council in the UK commissioned a roadmap on energy storage systems [17]. This roadmap targets a cost saving of around US\$80 per kWh between 2017 and 2035. During the same period, it also targets the energy density to double from 250 Wh kg−<sup>1</sup> to 500 Wh kg−<sup>1</sup> . Further, the UK is pressing ahead with the rollout of charging infrastructure to support the electric vehicle user—both a rapid charging network to support users as they move about the UK, but also workplace and home charging solutions to support commuters and shoppers [18,19]. In addition, there is also the consideration of subsidies that either reduce cost or make available preferential access to road infrastructure including toll roads, city centres and parking [20]. However, these incentives are likely to prove unsustainable in the long term, requiring a focus on vehicle and charging technologies [21].

charging technologies [21]. As energy storage costs are reducing, and technology is improving, this is encouraging OEMs to increase the battery capacity in their vehicles. What was fast charging for 16– 24 kWh batteries becomes not-so-fast when the battery size reaches 40, 60 or more kWh. As energy storage costs are reducing, and technology is improving, this is encouraging OEMs to increase the battery capacity in their vehicles. What was fast charging for 16–24 kWh batteries becomes not-so-fast when the battery size reaches 40, 60 or more kWh. Further, there will also be a requirement, if we are to decarbonise all road transport sectors, to focus on public high-power charging infrastructure in support of regional and long-haul freight operations along the trunk road network. Hence, to meet the expectations of the e-mobility stakeholders and drivers, charge head providers, such as CHAdeMO, are working on higher power charging. A new edition of CHAdeMO protocol enabling 200 kW to 400 kW charging was developed by the Association and its members, who are now

preparing for up to 900 kW [20]. Similar increases in charging capability are a feature of the EU's CCS system and CharIN is investigating versions up to 2 MW for electric trucks [21].

One potential challenge that the next generation of static charging technology faces is the integration of the charging stations into the existing electricity distribution grid. Recharging times are primarily becoming constrained by the electricity distribution infrastructure and not the technology of the charger/battery combination. Grid capacity is, therefore, a major issue impacting vehicle electrification and market appeal. The most obvious problem is the load increase, which can lead to a system overload since the components like transformers and supply lines are not designed to handle the extra loads requiring investment in reinforcement [22]. This leads to a juxtaposition, whereby the vehicle, through a combination of technology improvement and cost reduction has improved capability but places a requirement upon the charging system to make higher investments that need to be recouped from the system user. This tends to limit the geographical coverage of improved charging systems to where the initial investment can be recouped from higher demand or, conversely a higher operating cost for the system user.

The transition to electrification of road transport is further complicated by the diversity of different vehicle types and use cases. There is a relationship between the energy requirements of a specific modality and use case, and the ability to store energy on and transfer energy to the vehicle. Even with the development in battery technology and the reduction in cost through volume production, the difference that remains vis-à-vis fossil fuels means that replacement with electrification is not suitable for all sectors unless the frequency of charging events is substantially increased—to overcome the limitations upon on-board energy storage—and that those charging events are reduced in duration—the energy transfer rate is substantially increased in order to limit downtime, i.e., when the vehicle is stationary. As such, a transportation system based around the EV, and encompassing all possible modalities and use cases, would require the deployment of an electric refuelling infrastructure far in excess of the current fossil fuel refuelling infrastructure in order to address the driving range and recharging time limitations. These limitations have led to the discussion and exploration of various bespoke charging solutions for specific modalities and use cases, for example, the electrification of the PSV fleet in Eindhoven NL [23]

*"Recharging takes place at Hermes' depot via a wireless pantograph system on the roof of each bus. There are 20 rapid chargers for use during the day, 22 slow chargers for use during the night and 2 mobile chargers for the workshop. Alternating rapid and slow charging keeps the batteries in optimum condition. The 43 buses are used on 7 premium public transport bus line services and run at a frequency of 8 to 14 buses an hour. Eventually, 203 electric buses will be put into operation."*

Another example is commercial drivers, and specifically taxi drivers, where these barriers are more pronounced as a result of the longer distances covered compared to regular cars, and fewer opportunities for recharging. Results from a recent study [24] indicated that the current plug-in charging infrastructure does not facilitate charging opportunities for taxi trade, causing longer working hours lower earnings. Drivers reported running on a range extender petrol engine once the battery is depleted, limiting the environmental benefits of electric taxis. It was concluded that alternative charger systems, including wireless, could facilitate the increased driving range of existing electric taxis by encouraging opportunistic, short but frequent charging boosts [24].

Electric road systems (ERS) are an alternative set of charging solutions that have the potential to allow electric vehicles to drive longer distances on a single at base charge, without the need to increase battery sizes or to stress the distribution grid unnecessarily. ERS have a long history and encompass in-road wireless, in-road conductive, overhead catenary, etc. A number of studies have explored the concept of the electric road, but the focus has been primarily from a technical and use case point of view [25–29]. It is considered in these studies that it is unlikely that these systems will replace existing

charging systems but more likely complement (as for the PSV Eindhoven example, we create a charging ecosystem).

The most notable work concerning DWPT includes systems developed by the Korea Advanced Institute of Science and Technology (KAIST), Bombardier and Qualcomm. Other systems include the SIVETEC static WPT system developed by Siemens and the market-ready WiTricity static WPT system initially developed at Massachusetts Institute of Technology. DWPT has the potential to contribute to reducing the weight and the cost of those electric vehicles that have higher energy requirements and/or higher use intensity e.g., heavy goods vehicles or public service vehicles.

For DWPT to become a critical component of the charging ecosystem, a variety of technical challenges must be overcome. Appendix A illustrates how much existing research in the field has focused on debates surrounding technological issues. For example, Hutchinson et al. (2017) consider the technical practicalities of DWPT, whilst Gil and Taiber (2014) assessed the infrastructure challenges of introducing this technology. However, there is a lack of research into the electric road system as a whole. There is a requirement to look at the technical challenges in light of how this system is likely to be deployed and accepted by the user community.

The question that has to be asked is, what is the optimal configuration for successful integration of an electric road system as part of a wider charging ecosystem? The challenge is identifying the criteria that determine the success or limitations of DWPT and any dependencies that may exist between them. As there are multiple types of ERS, each having its associated strengths and weaknesses, the approach was to focus on the in-road dynamic wireless power transfer (DWPT) as this technology has strong adoption potential due to the ability to service multiple use cases—in-road DWPT has the potential to be deployed in multiple roadways (from urban to peri-urban through to motorway) and to service a wide range of different vehicle types (from passenger cars to public service vehicles and through to heavy goods vehicles) [4].
