The Potential Role of Flying Vehicles in Progressing the Energy Transition

Abstract

An energy transition is in progress around the globe, notably led by an increase in the deployment of renewable energy and a shift toward less emissions-intense options, notably in the transportation sector. This research investigates the potential role that new transportation options, namely flying vehicles, may play toward progressing the energy transition. As flying vehicles are a relatively new technology yet to penetrate the market, it is also prudent to consider the ethical, legal, and social issues (ELSI) associated with their implementation, alongside the potential energy and environmental impacts. Through a review of ELSI and energy and environmental literature, we identify research gaps and identify how flying vehicles may impact upon the energy transition over time. Our research identifies several critical aspects of both ELSI and energy and environmental academia relevant to the future deployment of flying vehicles and describes a deployment timeline and the resultant societal outcomes. We find that flying vehicles could drive the energy transition and the hydrogen economy and that their widespread adoption could engender shared socio-environmental benefits. Our findings are relevant to transportation and environmental policymakers and identify critical considerations for the planned introduction of new, shared transportation options to the market, conducive to a sustainable energy transition.

1. Introduction

The energy transition is gaining momentum around the globe due to a recognition of the potential future climate change impacts [1], leading governments to set ambitious carbon emission reduction goals [2,3]. The efforts toward reducing the impact of climate change which are most easily observed are occurring within the energy sector as these efforts often underpin other sectors, such as industry and transportation [4,5,6]. In spite of these ambitious policy targets, the current action toward mitigating climate change is not considered sufficient to keep temperature rises below the Paris 1.5 degree target [7].

As governments begin to move their goals beyond the Paris Agreement targets, in some cases toward carbon neutrality, there is a commensurate need to move beyond broad energy generation considerations, such as deploying more renewables or achieving a hydrogen economy, and to consider specific, niche applications. These niche applications may include industries which are hard to decarbonize, such as the cement industry [8], the introduction of commercial-scale carbon capture and storage (CCS), or even the introduction of more expensive carbon negative technologies [9]. Considering the transport sector, several low-carbon options already exist, including electric vehicles (EV) and fuel cell vehicles (FCV), utilizing electricity and hydrogen, respectively [10]. Flying vehicles represent an additional niche application within the transport sector and may rely on both electricity and hydrogen in the future [11]. Considering all of these technologies, it is prudent to consider the increased future material requirements for rare materials and the potential stresses this imparts on extraction practices, especially in developing nations [12]. If flying vehicle technologies are to make up a portion of the passenger transport sector in the future, it is prudent to understand the best ways to incorporate them in terms of their social, economic, and environmental costs and benefits.

This study seeks to understand the potential role of flying vehicles, focusing on urban and regional air mobility, played out through a review of the ethical, legal, and social issues (ELSI; [13]) associated with their introduction, as well as evaluating the economic and environmental issues associated with their use. In order to identify research gaps and extract policy implications for enhancing the role of flying vehicles toward advancing the energy transition, this review paper is structured as follows: Section 2 outlines the research methodology detailing the literature review focus. Section 3 details the findings of the literature review in terms of moral and legal issues, social acceptance, and energy and environmental issues. Section 4 summarizes the review findings and research gaps while detailing policy implications. Section 5 concludes the review and sets out the details of future work.

2. Materials and Methods

Recognizing that flying vehicles represent a new and emerging technology, the literature review leverages academic research from the past 10 years, focusing on our desired sectors to clarify the state of academic progress in this field. The issues we focused on are ELSI and energy and the environment, utilizing keywords relevant to each (see

Table 1. Literature Review Source Summary.

Theme	Keywords	Range	Type
Ethical, Legal and Social Issues (ELSI)	➢ Flying Cars/Air Taxi ➢ Urban air mobility ➢ Autonomous vehicle ➢ Safety management system ➢ Machine ethics ➢ Artificial intelligence ➢ Cybersecurity ➢ Transportation policy/safety ➢ Air corridors ➢ Collision avoidance ➢ Acceptance ➢ Safety/Security	2015–2022	➢ Articles ➢ Books ➢ Conference Proceedings ➢ Reports
Energy and the Environment	➢ Energy Management ➢ Sustainability ➢ Cost-benefit analysis ➢ Vertical take off ➢ Green transportation ➢ Driving behavior ➢ Energy consumption ➢ Emissions	2017–2022	➢ Articles ➢ Conference Proceedings ➢ Reports

for details). For example, for ELSI we examined moral issues surrounding accidents and autonomous decision making, legal issues focusing on developing flying lanes, law enforcement, and infringement on individual rights, and social issues such as acceptance and awareness. These issues are critical to be overcome for flying vehicles to be able to participate in the transport sector and they precede the consideration of our main concern, which are the energy and environmental issues required to be overcome for flying vehicles to not only play a role in the transport sector but to advance the energy transition. In terms of energy and the environment, our literature review focused on issues of infrastructure, both in terms of use and charging, and the carbon emission impacts. Figure 1 details the focus and desired outcomes of our review.

Specifically, the literature review methodology is based on keyword combination searches in Scopus filtered by field, type, and year, as detailed in Table 1.

From Table 1, we observe that the more recently investigated energy and environmental literature does not contain any book sources, likely due to the recency of investigation of this theme. Though not exhaustive, the review seeks to uncover the critical aspects and research gaps across ELSI and the energy and environmental issues related to flying vehicles, cognizant of an overlap between the themes. The literature review aims to cover a broad range of literature by utilizing an iterative search regime, beginning with simple common terms such as ‘flying cars’ or ‘air taxi’ to gauge the breadth of general literature before focusing on critical issues within ELSI and energy and environmental issues. This is achieved by using a combination of search terms (utilizing the ‘and’ operator in Scopus) exhaustively for all keywords detailed in Table 1. The 10 year time limit applied ensures that the academic literature is recent and relevant due to the fast pace of technology development in the flying vehicle space [14], evidenced by the range of results derived, only going back as far as 2015 for our investigation of the relevant ELSI-related literature. In the energy and environmental space, relevant literature is only found post-2017. In order to bolster search results, and to incorporate the most recent academic and technological findings, Scopus-indexed conference proceedings as well as reports from the relevant international agencies and commercial bodies are also included where necessary.

3. Results

The literature review is undertaken across the two main themes of ELSI and energy and the environment, as detailed below, in order to provide an evidence base for the consideration of the potential contribution of flying vehicles toward an energy transition.

3.1. Ethical, Legal, and Social Issues (ELSI)

Here, we focus on moral, legal, and social acceptance issues toward flying vehicles cognizant of anticipated infrastructure and societal changes.

3.1.1. Moral Issues

In terms of flying and autonomous vehicle moral issues, a number of factors have been studied, particularly around accidents and moral dilemmas. For example, to date, 68% of aircraft accidents have occurred as a result of human participation, suggesting that automated operation may improve safety outcomes [15]. A classic dilemma, coined the “Trolly Problem” (a thought experiment in ethics which was first devised by the Oxford moral philosopher Philippa Foot in 1967; a moral dilemma which involves tradeoffs between causing one death in order to prevent several more) has been weighed up over the years and with a specific focus on autonomous vehicles in recent years, i.e., through a study focusing on the ethics issues and importance of adding an ethical dimension to machines [16]. A specific approach to reducing small unmanned aerial vehicle (UAV) safety impacts through regulations in Japan was investigated, demonstrating the ability to meet stakeholder expectations by utilizing a system-theoretic accident model and process, with implications for policy makers [17].

It has been suggested that moral algorithms for autonomous vehicles (AVs) create a social dilemma, where people identify support for AVs that will sacrifice their passengers in order to minimize the number of causalities on the road; however, these same people also want to buy and utilize AVs that will protect passengers as a priority [18].

For use in autonomous machines, three advanced logics have been proposed including Deontic (logic for statements of permission and obligation), Epistemic (logic for statements of beliefs and knowledge), and Action (logic for statement about actions) logics, which ideally will work as a bridge between machines and ethics. These logics provide a way to state explicitly what actions are allowed and which are forbidden [19]. It has also been proposed that engineers must teach the elements of good judgement to cars and other self-guided machines [20].

From a different angle, it has been argued that the “Trolly Problem” will be solved not by ethicists but by lawyers, as any collision on the road by vehicles controlled by artificial intelligence (AI) will be attributed to the vehicle maker, and that the “Trolly Problem” will be solved democratically through a combination of legal liability and consumer psychology [21].

A team at the Massachusetts Institute of Technology (MIT) developed an online platform called “MORAL MACHINE” which gathers human perspectives on moral decisions made by machine intelligence, such as self-driving cars. The machine incorporates people’s ethical intuitions from a large-scale survey on the moral issues related to self-driving cars. The results of the study identified the range of moral issues that manufacturers of autonomous cars need to be sensitive to when designing and selling their products [22].

3.1.2. Legal Issues

Flying cars are required to communicate a multitude of information including position, speed, altitude, etc., often wirelessly. It is likely that issues will arise regarding cybercrime and potential terrorism, covered in a number of studies to date [23,24,25]. A discussion about ensuring adequate law enforcement systems to prevent the misuse of these technologies is also considered essential [26].

The idea of designing virtual highways in the sky has been suggested to achieve collision-free traffic control [27,28]. Lowry presents the concept of a four-segment airspace which divides traffic according to its direction in order to reduce the risk of collision in the air [29]. In addition to virtual highways and traffic controlling infrastructure, some attention has been given to the potential impacts of weather on the safety, cost, and efficiency of urban air mobility (UAM) [30]. Air congestion, landing pad, air traffic control, and ELSI issues were also anticipated in future smart city applications for UAV taxis [31].

Low-altitude flying is likely to lead to noise pollution and understanding the impacts of community noise that is created around vertiports and along air routes is crucial. Efforts to reduce community noise from future UAM traffic management is already being considered [32]. A study on inviting residents to actively participate in noise sensing through free smartphone apps (known as participatory noise sensing (PNS)) is a possible solution to help mitigate noise issues [33]. Advancing battery technology will enable propellers to rotate at lower speeds than for conventional rotorcraft which may help to combat environmental challenges such as pollutant and noise emissions in densely populated cities [34].

Coexisting with human-driven cars during the transitional period has generated some discussion regarding the safe joint use of infrastructure. For example, a study was undertaken on how reserved lanes for autonomous vehicles in three different strategies can reduce congestion [35], while the risks were highlighted through the simulation of scenarios including the overtaking of autonomous vehicles by manually driven vehicles at illegal speeds [36]. The need to fuse the existing and leverage new sources of data to enable the future transport regime was also elucidated [37].

3.1.3. Public Knowledge, Concerns, and Social Acceptance

Electric vehicles are well known to the public, even among young children, demonstrated by a survey of 587 schoolchildren in Denmark and the Netherlands aged between 9 and 13 identifying their awareness and knowledge about EVs and their concerns regarding high prices and overall environmental impacts [38,39].

Further, the high cost of UAM and flying cars may cause social segregation. Through an investigation of the perceptual patterns of individuals towards travel time, cost, environmental benefits (such as lower CO² emissions) and the challenges arising from flying cars’ operational characteristics, it was found that flying cars threaten to magnify the effects of both sociopolitical and environmental issues arising from short regional flight usage [40].

At the commercial level, the overall vision is to offer flights at a price point that generates a regular demand. To bring costs down, the annual production of flying cars needs to reach a level sufficient to trigger significant economies of scale. Research has identified various pricing and trip scenarios as well as the benefits and concerns that will arise from the introduction of flying cars. The findings provide some insights regarding the critical challenges that should be addressed by policymakers, regulators, and manufacturing companies to enable social acceptance [41].

While traditional airlines offer more space and catering services, UAM can instead offer a fast and efficient flight time with short waiting times for onboarding through passenger-centric scheduling, i.e., flight routing and recharging solutions. The allocation of various passenger classes with different charging times could also contribute to addressing UAM affordability concerns [42].

In terms of security, the analysis of a survey of 584 individuals in the US in 2017 identified some insights into public perceptions towards various issues. With regard to “Security measures”, 75% of participants thought it necessary to check the flying car owners or operators’ background in detail. Seventy-one percent thought it necessary to have air-road police enforcement with flying police cars, while 79% thought it necessary to establish no-fly zones near sensitive locations [43]. An additional survey of 1125 people from the US and India highlighted that consumers’ primary concerns were about the safety and security of both vertiports and vehicles [44]. An online survey of 1164 participants in China identified both a good understanding of autonomous vehicles and a positive impression towards them. The results also showed an expectancy of lower user insurance premiums; however, 48% of participants identified a desire to increase third-party liability insurance and a total of 69% of respondents identified a willingness to pay more for autonomous vehicle insurance overall [45]. In terms of perceived risks and benefits, it was identified that end users expected autonomous vehicles to overcome human limitations and free up time, however the risk of autonomous vehicles not living up to expectations was also identified [46].

Finally, research was also identified which dealt with motion sickness in autonomous vehicles and the impacts on the users of vehicles. With regard to customer satisfaction, reducing the occurrence of motion sickness while giving passengers the ability to perform necessary activities while in transit also needs to be addressed [47].

3.2. Energy and the Environment

Following on from the ELSI concerns, here we investigate the recent scholarship on energy requirements and environmental issues, focusing on carbon emissions.

3.2.1. Energy

Though flying cars will ideally reduce both travel time and carbon footprints [48], due to requirements that they are lightweight to be able to get off the ground without using too much energy, they are often designed for small numbers of people, and are not efficient on short trips [49].

A physics-based analysis of primary energy and GHG emissions of VTOLs vs. ground-based cars showed that tilt-rotor/duct/wing VTOLs are efficient when cruising, but consume a substantial amount of energy for takeoff and climbing [50]; hence, their burdens depend critically on trip distance [48].

If flying cars will rely on electric motors in the medium term, battery technology needs to be significantly improved to enable a safe and convenient VTOL operation. Batteries which provided the energy for flying vehicles will need to be safer, faster charging, smaller, and lighter than those used in EVs [51]. Current efforts in this space are being investigated commercially, for example by the Lilium company, who is having megawatt-scale chargers developed which will enable battery charging in 30 min, or to 80% within 15 min. This level of charging capacity is expected to enable 20 to 25 flights per aircraft, per day [52]. The need for massive infrastructure investment and utilization of fit-for-purpose charging regimes has also been investigated in some detail for the sustainable use of UAVs [53,54]. The charging infrastructure for flying vehicles is multiple times higher than that for EVs, which range between 7 kilowatts (kW) for overnight charging and 145 kW for rapid charging, while flying vehicle chargers are anticipated to draw up to 600 kW and even megawatt (MW) levels [55].

Alternatives to batteries, including low carbon fuels such as hydrogen, are already being tested as viable option, for example by the Skai system, which can refuel its onboard hydrogen tank in less than ten minutes [56]. The use of hydrogen generated from renewables (green hydrogen) comes with its own storage and distribution issues. When considering the techno-economics of battery and hydrogen vehicles, it was found that hydrogen is technologically superior when urban air mobility requires ranges greater than 60 miles, however that hydrogen fuel cell vehicles will need to reduce costs considerably to be competitive with battery-powered options [57].

3.2.2. Environment

The potential effects on GHG emissions are uncertain, with driving conditions critical to impacts. The potential contributors to GHG emission reduction are eco-driving and platooning (the practice of a group of vehicles driving together to save energy), which has a significant contribution to reducing GHG commissions by up to 35%. On the other hand, faster travel and increased reliability needs can contribute to the increase in GHG emissions by 24% and 41%, respectively [58].

Research suggested that traveling 100 km in a flying car with 4 occupants is more environmentally friendly than average EV making the same trip by road. Distance-dependent analysis reveals that electric vertical takeoff and landing (VTOL) vehicles emit more greenhouse gases (GHGs) than internal combustion engine (ICE) vehicles at trip lengths under 35 km, but quickly become the greener option at distances beyond that [59].

By incorporating technology (sensors and localization and mapping algorithms) to avoid collisions, autonomous vehicles can provide collective fuel saving and environmental benefits by reducing traffic congestion that might increase the chance of accidents [58].

In developing and engaging the appropriate infrastructures to enable a shift to autonomous and flying vehicles, there is an opportunity to increase the amount of renewable energy used in the grid, engendering sustainability and emission-reducing benefits which could be considerable when combined with a shift to a sharing economy, as espoused by autonomous vehicle proponents [53]. Even in the early phase of flying vehicle deployment where the majority of energy for charging comes from fossil fuels, grid-level improvements toward decarbonization will be reaped [60]. The shift toward electric aircraft has been identified as a potential contribution toward the decarbonization of air transport, thus mitigating climate change both for short and long flight aircrafts [61]. It was also identified that transport service providers place a high importance on the provision of environmentally friendly air-transport in the future, including door-to-door air travel [62].

If flying vehicles diversify fuel use beyond batteries toward hydrogen or other low-carbon fuels, the opportunity to decarbonize the grid is also diversified and further carbon-reducing opportunities, alongside infrastructure challenges, will be realized [63]. The challenge here is to ensure that hydrogen is derived from clean energy sources, which is not currently the case, with the majority of low-carbon hydrogen utilizing CCS [64], i.e., blue hydrogen. It is hoped that green hydrogen can be developed in the future, in line with advancing learning curves for renewable energy, hydrogen production, storage and distribution technologies. In the European Union, along with general positive attitudes toward urban air mobility, people expressed an expectation that flying vehicles would help reduce emissions overall, through reduced traffic congestion and better air quality [65].

4. Discussion: Identified Gaps and the Potential Role of Flying Vehicles in Progressing the Energy Transition

Deploying flying vehicles for use in passenger transport and the progression of the energy transition are not mutually exclusive goals, for a number of reasons. First, transition theory states that an increase in the need for energy to improve convenience or lifestyle outcomes (such as cleaner air, etc.) is a critical factor for speeding up the energy transition [66]. An example is electrification, whereby processes such as lighting, heating, and transportation shift away from fuel sources such as gas, kerosene, and gasoline in preference for the use of electricity. Electrification benefits the end user in that immediate environmental conditions are improved; however, the underpinning source of this electricity is still overwhelmingly derived from fossil fuels. Due, however, to the existence of a comprehensive electricity grid to distribute electricity to the end user, it is simpler to green the production side incrementally as more renewable energy comes online, or carbon-reducing technologies such as CCS are deployed [53]. Relevant to flying vehicles is the increased need for electricity for charging, offering opportunities to provide the additionally required energy from renewable sources and to progress the clean energy transition. Likewise, if future flying vehicles utilize hydrogen as their fuel source, there is a likelihood that hydrogen production, storage, and distribution infrastructure will mature as a result.

Further, considering the socio-technical regime, norms are also very important in achieving an energy transition. These norms extend not only to the desire for additional renewable energy to be deployed, and the added convenience experienced through personalized air transport, but also to the notion of a sharing economy. As flying vehicles are anticipated to take the role of taxis or public transport, they will not be purchased for personal use, as is the case for passenger cars, thus the emission avoidance benefits and costs will be shared by all users. Further, as the notion of a sharing economy expands, and road-based transport also potentially shifts toward a shared model, in combination with the benefits engendered by the use of flying cars, it is reasonable to expect that personal vehicle ownership will also decrease. The elimination of a portion of personal use vehicles has a dual benefit: first by reducing the material requirements for the production of vehicles which are dormant for the majority of their serviceable life (i.e., parked 95% of the time; [67]), and second by reducing per-capita transport emissions through the inefficient use of cars (i.e., large cars driven with only one or two passengers). Figure 2 outlines the potential deployment timeline of flying vehicles and the envisioned socio-environmental benefits as a result.

To ensure an understanding of the potential benefits of the deployment of flying vehicles, it is important to also note the challenges which will need to be overcome. First among these challenges is the need to provide large amounts of electricity for charging in a very short period of time, safely and efficiently; without such infrastructure, convenience cannot be assured. The use of rapid charging also has ramifications on battery use, particularly for lithium-ion batteries which required temperature control and have degradation issues, including lithium plating and graphite exfoliation in some cases [68]. Manufacturing processes must enable lithium-ion batteries to sustain a repeated fast charge at ambient temperatures. Further to the issue of battery design, the consistent provision of electricity from multiple sources is also critical, especially when considering the incorporation of renewables and energy storage media [69]. The choice of infrastructure for charging is also critical, and may consider traditional wires, induction, or even battery swapping [70].

Future flying vehicles may take advantage of hydrogen as a fuel source, which, while overcoming some of the issues surrounding battery charging technologies, requires the development of a hydrogen economy and the broad deployment of hydrogen compatible infrastructure. While enthusiasm exists towards the hydrogen economy, it is still in the nascent period, and a clear stakeholder choice between electric or hydrogen-based personal transportation is yet to emerge [63], and the deployment of hydrogen infrastructure may have the financial ramification of a more expensive energy system overall [64]. As hydrogen and electricity both have the potential to be derived from renewable and low-carbon sources, their employment in underpinning the emergence of flying vehicles will have a positive impact on progressing the energy transition.

5. Conclusions

A review of the literature across the ELSI and energy and environmental issues related to flying vehicles identified the current state of academic investigation into moral, legal, and social acceptance issues, and to a lesser degree, the energy and environmental issues requiring redress. Although, moral, legal, and social issues can be interpreted through the lens of existing systems and through stakeholder engagement. For the emerging technology of flying vehicles which have the potential to revolutionize passenger transport, limited investigation has been undertaken on the energy requirements and potential flow-on environmental impacts. Even the infrastructure which will underpin flying vehicles is not certain, much in the same way as EV and FCV technologies compete to become the dominant form of passenger road transport fuel, either via hydrogen or electricity.

Once a roadmap of the energy and infrastructure needs, desirable fuel sources, and potential use cases can be clearly defined, there is a strong need to evaluate flying vehicles from a sustainability point of view, i.e., to consider the economic, environmental, and social issues which emerge under a holistic framework. These evaluations will fill the gaps identified in this literature analysis and aid policy makers to develop policies cognizant of the important issues which may help or hinder the deployment of flying vehicles in such a way that they not only increase transportation options and convenience, but also aid in progressing a sustainable energy transition.

While this research seeks to identify the potential role of flying vehicles toward the energy transition and improving energy efficiency and environmental outcomes, one key limitation is the high level of uncertainty surrounding flying vehicles’ penetration of the market and their level of social acceptance. As the body of literature increases over time, it is hoped that these questions can also be addressed, so as to provide policy evidence to underpin infrastructure and energy system considerations for flying vehicle implementation.