The book titled “Graphene-Based Nanotechnologies for Energy and Environmental Applications”, edited by Mohammad Jawaid, Akil Ahmad and David Lokhat, focuses on recent developments in graphene-based materials, composites and devices for a variety of applications in storage devices, supercapacitors, water treatment, ion-separation, photocatalysts and antimicrobial applications. It is part of the series Micro and Nano Technologies published by Elsevier. The first editor of the book, Mohammad Jawaid from the Universiti Putra Malaysia, has expertise in nanomaterials (particularly graphene materials) and their composites and has significant research output with a h-index of 53. The second editor, Akil Ahmad, currently a postdoctoral researcher at the University of KwaZulu-Natal, South Africa, has worked on nanomaterials synthesis and applications of nanomaterials in wastewater treatment. David Lokhat, the third editor of the book from the University of KwaZulu-Natal, has been working on reactor and extraction technologies.

The book is divided into three major parts: Introduction, Energy and Environment. Each category has many chapters written by diverse authors. A total of 59 authors from different affiliations contributed to the different chapters. Firstly, the introduction covers basic terminologies and definitions of nanotechnology, nanomaterials and provides specific literature background on graphene-based materials and their composites for energy and environmental applications. Ahmad et al. collected literature on graphene-based nanotechnologies, which covers the latest developments in graphene research around the world, and David Lokhat contributed towards energy and environmental applications leveraged by graphene derivatives along with publication statistics. Production methods, characterisation methods and properties of graphene and its applications in different areas are covered. The literature and data were collected and compiled from over 350 publications. Every chapter has a conclusion or concise summary with potential prospects for the future in each research or subject area.

Mamvura et al. (University of South Africa) have written a chapter on renewable energy systems using graphene derivatives. The chapter covers applications of graphene in battery-powered vehicles, fuel cells, solar cells and energy storage devices. Mohamed I. Fadlalla and Sundaram Ganesh Babu (University of Cape Town, South Africa) presented a chapter on graphene materials in photocatalytic water splitting for hydrogen production. Topics such as mono- or bi-semiconducting catalyst and metal and non-metal doped graphene-based photocatalysts for water splitting applications are covered. Umar et al. (Universiti Sains Malaysia) included topics on metal decorated graphene nanocomposites for energy storage applications. Their chapter is mainly focused on metal-based composites, solar and fuel cells, supercapacitors and lithium-ion batteries and mechanisms of energy conversions are covered in detail. A chapter on graphene oxide (GO) for hydrogen storage applications was written by Azim et al. (University of KwaZulu-Natal). Composites of GO and reduced GO with metal oxides, carbon nanotubes and organic materials and relevant fabrication methods are well elaborated in this chapter. Professor Mohammad et al. (King Saud University, Saudi Arabia) have contributed a chapter towards graphene-derived nanocomposites as supercapacitors and electrochemical cells. This chapter includes the synthesis (Figure 1) and physical properties of graphene nanosheets, a section on biosensors and a short note on supercapacitors produced from graphene nanocomposites. Jean Mulopo and Jibril Abdulsalam (University of the Witwatersrand, South Africa) have provided a chapter on graphene-based energy storage applications (capacitors, batteries, fuel cells and solar cells) with an emphasis on electrical and thermal conductivity, specific surface area and specific heat properties.

Fig. 1

Overall, this section of the book with six chapters covers a wide range of electronic devices incorporating graphene and its derivatives. In-depth analysis and data have been included from a significant number of publications and research works. Topics on graphene composite as air filters, gas sensors, volatile sensors, liquid sensors, radiation sensors and pollutant sensors are adequately discussed in these chapters.

The section of the book begins with a chapter on graphene-based sensors for the detection of volatile organic compounds (VOCs) written by Ansari et al. (Aligarh Muslim University, India). Graphene with metal additives as sensors and their functioning mechanisms have been well discussed in this chapter. Haseen et al. (Aligarh Muslim University) concentrated on the application of magnetite-GO composite for wastewater treatment. This chapter covers magnetite-GO for specific dispersive solid-phase extraction. Mohamma Laskar and Sana Siddiqui (Jazan University, Saudi Arabia) focused on GO-based filters for solid-phase extractions, including nascent GO, chelates adsorbed GO, functionalised GO with external molecules and specific GO nanocomposites. GO functionalised with magnetic molecules and their composites with polymer or metal matrices have been extensively studied. Reduced GO (rGO) derivatives for such applications are also included.

A chapter by Kumar et al. (King Abdulaziz University, Saudi Arabia) covers graphene-metal oxide composite photocatalyst for degrading water pollution. Structure and property (chemical and physical) relationships and the effect of graphene’s bandgap on photocatalytic decomposition are interpreted. The mechanism of photocatalysis for relevant graphene materials and metal-GO and rGO composites are included. Hussain et al. (Jubail Industrial College, Saudi Arabia) collated information on a new generation of GO for removal of polycyclic aromatic hydrocarbons from a wide range of literature and new results. The chapter covers several properties of graphene, such as mechanical, electrical and thermal properties and their influence on the interaction of polycyclic aromatic hydrocarbons as well as the role of GO as an adsorbent for such hydrocarbons. A chapter by Ng et al. (UCSI University, Malaysia) is dedicated to graphene-based membranes for separating hazardous contaminants in wastewater. This is probably the only chapter that gives importance to both polymer-based and metal-based graphene composites for the targeted application. Traditional thermoplastics (polystyrene, polyvinylidene fluoride, polyamide-imide, polyacrylonitrile and polyethersulfone) composites and conducting polymer (polyaniline)-based graphene composites are organised with their fabrication process and efficiency as a membrane in a descriptive manner.

Hossain et al. (Universiti Sains Malaysia) focused on antimicrobial activity of graphene-based materials. The antimicrobial mechanism of major graphene derivatives (GO, rGO and graphene) are discussed along with the performances of their composites with hydrogel and polymer dispersions. The effect of toxicity of graphene materials on antimicrobial activity adds to the value of this chapter. Graphene-metal oxide hybrid composites for treating textile dyes are discussed in a chapter by Shahadat et al. (Indian Institute of Technology, Delhi). This short chapter attempts to add to the knowledge of graphene-metal synthesis for removal of industrial dyes and provides details of the effects of functional groups (hydroxyl, carboxyl and oxygen) present in the composite systems on their performance. Reddy (Universiti Teknologi PETRONAS, Malaysia) and co-authors emphasised graphene nanomaterials for removal of pharmaceutical compounds in drinking water. The impacts of surface functional groups, sorption kinetics, pH and temperature on absorption stability of graphene-based materials and nanocomposites are discussed in detail. Research data on polymer-based, ceramics-based and metal-based composites are also covered in this chapter. Two chapters, by Yadav et al. (Shree Velagapudi Ramakrishna Memorial College, India) and Abbas et al. (Universiti Sains Malaysia), focus on the application of graphene composites in air quality and wastewater treatment. Figure 2 depicts different applications in which graphene nanocomposites can be utilised.

Fig. 2

Each chapter provides solid knowledge in its prescribed subject matter, and they read and flow well. However, looking collectively, there are several duplications and repetitions found in the book, especially the synthesis of graphene and applications such as storage devices and water treatment. These chapters are written using different language, and the knowledge is not very diverse. Another major flaw of the book is that it has missed out on the latest developments in graphene-based polymer composites and their multifunctional applications in energy and environment, which is a significant subject area that is expected to be covered in a book like this. There is only one chapter (Chapter 15) that covers sufficient polymer-graphene composites in the removal of hazardous contaminants from wastewater. Other application areas related to energy and environment are completely neglected. Furthermore, while most chapters have excellent illustrative figures, a few chapters do not have a single figure. It is always better and more attractive to have figures to effectively convey scientific concepts and processes. The summary in each chapter is concise, and future prospects are given appropriately. The front cover, preface, table of contents, index and back cover are suitable and sufficient.

Summing up, this book provides useful knowledge predominantly in graphene-based materials for storage cells, sensory and wastewater treatment applications.

Global car and truck manufacturers, along with their supply chains, have made huge steps to minimise vehicular emissions since the advent of the internal combustion engine (ICE). Of particular note are the criteria pollutant emissions regulations, which have focused on reducing the tailpipe carbon monoxide, hydrocarbons, nitrogen oxides (NOx) and particulate matter (PM) emissions from the global vehicle fleet. For example, since the first European regulations were introduced in the early 1990s, the permitted NOx emissions of cars have dropped by almost a factor of 15, which has been enabled by close collaboration between the car manufacturers and the substrate and catalyst suppliers. More recently, the focus has shifted to CO₂ emissions, as governments and regulators work towards the implementation of measures to enable the Paris Agreement climate change commitments to be met (1). Indeed, the latest view of the Intergovernmental Panel on Climate Change (IPCC) is that there are significant benefits in targeting a maximum temperature increase of 1.5°C over pre-industrial levels, rather than the 2°C Paris Agreement target, and this 1.5°C target essentially means that CO₂ emissions need to reduce to net zero globally by 2050 (2). This is an extremely challenging target, with massive implications for all energy-hungry sectors such as transportation, which currently accounts for around 24% of global CO₂ emissions (3). Moving the transport segment to net zero by 2050 means that only vehicles with zero CO₂ emissions can be sold from 2040 or earlier, to avoid legacy fleet emissions, since cars, buses and trucks typically stay in use for 10 years or more. Indeed, the recommendation of the Committee on Climate Change (CCC), the UK Government’s independent advisor on climate change, is that introduction date of the ban on vehicles powered by ICE should be brought forward from 2040 (which was the original plan) to 2035 “at the latest” or, more preferably, 2030 (4). Currently, around 1% of new passenger car sales globally do not have any tailpipe CO₂ emissions (that is, they are regarded as zero emission vehicles (ZEVs)) with almost all of these being battery electric vehicles (BEVs). There are far fewer zero emission commercial vehicle sales, so the automotive industry has a long way to go on its journey to net zero.

The two principal ZEV ground transportation options are the BEV and the fuel cell electric vehicle (FCEV). BEVs use electricity to charge the battery to provide motive power, while FCEVs use an electrochemical cell to convert the chemical energy of hydrogen (supplied from an on-board tank) and oxygen (from the air) into electricity. There are several types of fuel cell, but the one most applicable to transport applications is the polymer or proton electrolyte membrane (PEM) fuel cell (also called proton exchange membrane fuel cell), which starts up rapidly, operates at low temperature, and delivers high power density at low weight or volume compared to other fuel cells.

In some geographies there are discussions on whether biofuels or power-to-liquids, also known as e-fuels, can play a major role in the decarbonisation of the transport sector. In this context, a biofuel is a liquid or gaseous fuel produced from biomass or waste, and an e-fuel is a fuel generated through the use of renewable electricity to generate hydrogen which is then attached to carbon from CO₂ for subsequent conversion into hydrocarbon fuels similar to those used today.

Biofuels can be ethanol, methanol, fatty acid methyl ester (FAME), hydrotreated vegetable oil (HVO), biomethane (either compressed or liquefied) or advanced biofuel such as biodiesel or bio jet fuel. These biofuels can be split into generations of biofuels:

Biofuels were first introduced in the hope of reducing carbon intensity of fuel, since in a simplistic sense the CO₂ generated by combustion is absorbed by the regeneration of the crops used to make it, and because they can be blended into fossil fuels without the need to modify engine technology.

First generation biofuels do not represent good decarbonisation options since when both direct and indirect emissions are taken into account (for example, from changes in land use), such biofuels are often only a marginal GHG emission improvement over fossil fuels, and in some cases actually have higher emissions (5). Sustainable advanced biofuels are based on wastes and residues, so their potential contribution to fuel requirements is finite. The industries that typically contribute the most to advanced biofuels are agriculture and the food industry (through residues such as organic waste sludges, manure or straw) and forestry industries, especially in the Nordics (from saw and pulp mills). Biomass resources are also already well utilised, so if the current consumption in other areas (for example, paper production) is assumed to continue, the maximum biofuel production would be able to supply around 8.5% of all road transport in the EU (5). However, the aviation and marine sectors are already making their case to use these biofuels, so while they may make a contribution to reducing road transport CO₂ in the short term (via blending into current hydrocarbon fuels), it is not expected that they will make a major contribution in the medium term and beyond.

For e-fuels, the first step in their production is to generate hydrogen via water electrolysis using renewable electricity. Hydrogen is then combined with CO₂ to form hydrocarbon fuels, with the CO₂ coming from, for example, industrial or biogenic sources, or from the direct capture of CO₂ from the air (direct air capture (DAC)). At the present time, industrial CO₂ emissions are regarded as ‘waste’, but capturing this CO₂, converting it into a hydrocarbon fuel, and then combusting it still leads to its release into the environment, and in the medium to long term it is expected that the CO₂ sources will either need to be from DAC or from ‘green’ sources such as biomass combustion.

The technologies to convert CO₂ and H₂ into both synthetic natural gas (SNG) and methanol at scale are known, and it can be expected that processes at early technology readiness level (TRL) currently under development (for example, direct electrochemical synthesis) will get more attention should there be a market. To produce e-fuels the SNG and methanol can undergo further conversion, for example to dimethyl ether or via the methanol-to-gasoline process to gasoline. However, not all pathways to the higher value e-fuels are commercially viable, and indeed the most attractive product to make, kerosene, is not accessible today as there is no large scale implementation of the reverse water gas shift reaction, which converts CO₂ into CO, which is the active carbon species in the Fischer-Tropsch reaction. Today the process is used to convert gas and coal to liquid fuels, but there are several projects focusing on the conversion of biomass and waste to liquid fuels.

The attraction of e-fuels in the form of the hydrocarbon fuels used today is that they can be a direct drop-in for current fuels, using the same distribution network and being burned in the same kind of engines that we have today. In some applications, such as aviation and marine, their use seems likely, as discussed elsewhere in this edition of Johnson Matthey Technology Review, since liquid fuels are expected to be required for a substantial period of time in these areas due to challenges with the use of battery or hydrogen fuel cells in such applications. For ground transportation, however, their widespread use seems less likely for several reasons, including:

So, while it is expected that biofuels and e-fuels will play a significant role in the aviation and marine areas, the focus of this article is on ground transportation, where BEVs and FCEVs are expected to be the major technologies. This is consistent with, for example, the views of Martin Daum, Member of the Board of Management of Daimler AG, responsible for trucks and buses:

“Truly CO₂-neutral transport only works with battery-electric or hydrogen-based drive” (7).

The regulations in the passenger car and commercial vehicle sectors focus on emissions from the tailpipe, and historically the main focus has been on criteria pollutants, which have enabled major improvements in urban air quality to be made. The focus is now shifting to CO₂, and Figure 1 shows the current and incoming CO₂ regulations for cars in various countries and regions around the world (8), illustrating the substantial reductions required going forward.

Fig. 1.

The European regulations for 2025 and 2030 require reductions of 15% and 37.5% respectively over the 2021 legislation. These regulations are intended to continue to drive the decarbonisation of the automotive industry, and the fleet average CO₂ emissions required in 2030 will require extensive electrification of the fleet. Indeed, Herbert Diess, CEO of the VW Group, has stated that these 2030 regulations will require at least 40% of VW’s European sales to be electric vehicles (BEV and plug-in hybrid electric vehicles (PHEV)) in 2030 (9).

Legislation on CO₂ and GHG is also tightening in the commercial vehicle sector, with the next set of European regulations requiring a 15% drop in CO₂ emissions from today by 2025, and a 30% reduction from today in 2030. This 2030 target is expected to lead to significant hybridisation of the commercial vehicle fleet, along with some completely electrified vehicle sales. Trucks, buses and coaches are responsible for about a quarter of CO₂ emissions from road transport in the EU and for some 6% of total EU emissions (10), so introducing low and zero emission vehicles in this sector is critical to support global moves towards net zero.

The electrification of the bus market is already underway, with over 400,000 battery electric buses in use in China today (out of around 425,000 BEV buses worldwide). Some Chinese cities, such as Shenzhen, have completely transitioned to battery-powered buses, with around 16,500 such vehicles on the road. Many other cities worldwide are committed to moving away from diesel and towards zero emission buses in the coming years. For example, 13 cities have signed the C40 Fossil Fuel-Free Streets Declaration (11), and will procure only zero emission buses from 2025. These are: Auckland, Barcelona, Cape Town, Copenhagen, London, Los Angeles, Mexico City, Milan, Paris, Quito, Rome, Seattle and Vancouver. London has committed to increase its BEV fleet from 120 to 300 by 2020, and in Paris 80% of the fleet will be e-buses by 2025. Oslo has gone further, and will have fossil fuel-free public transport by 2020, while in the Netherlands all new buses will be zero emission by 2025, with the whole fleet being all‐electric by 2030. These commitments will lead to improved urban air quality and a reduced CO₂ footprint, as long as the electricity used to charge the buses is from low carbon sources, as discussed later.

California often takes a mandate-based approach to regulations, in order to drive the development and initial implementation of new technologies. Within the commercial vehicle sector they are proposing an Advanced Clean Trucks mandate, which will require original equipment manufacturers (OEMs) with more than 500 truck sales in California to sell an increasing proportion of zero emission trucks, starting in 2024, per the schedule outlined in Table I. The intention of the California Air Resources Board (CARB) is to accelerate the first wave of zero-emission trucks, which are seen as essential if net zero targets are to be met, particularly since the commercial vehicle market is widely regarded as being significantly more difficult to decarbonise than the passenger car fleet. The schedule outlined in Table I will lead to a ZEV truck fleet of around 100,000 vehicles on California’s roads in 2030, rising to around 300,000 in 2035.

Of course, tailpipe emissions are only part of the CO₂ story, since the emissions associated with the manufacture of the vehicle and the fuel also need to be considered in any holistic analysis. For BEVs the manufacture of the battery generates significant levels of CO₂, estimated to be around 175 kg CO₂ kWh^–1 of battery capacity (12), and with vehicle batteries typically having between 30 kWh and 100 kWh of stored energy, this leads to upstream emissions of 5–17.5 tonnes of CO₂ per battery pack. In addition, the electricity used to charge the battery has associated CO₂ emissions, unless it is generated from renewable sources such as wind or solar power. For example, UK electricity currently has a carbon intensity of around 200 g CO₂ kWh^‐1 (13), which is below the average of European Union countries, while Norway (extensive use of renewable hydroelectric power) and France (predominantly nuclear power) have much lower carbon signatures.

The hydrogen used to power FCEVs is typically generated in one of two ways: either through electrolysis (in which an electric current is used to split water into hydrogen and oxygen) or the steam reforming of methane. The former route is, therefore, subject to the same CO₂ emission challenges (and opportunities) as the BEV, while the latter route generates relatively high levels of CO₂ which in future will need to be abated using carbon capture utilisation and storage (CCUS) technology, in which the CO₂ generated by the process is captured with high efficiency (which can be around 95%) and then either stored (for example, in depleted oil and gas fields) or used for other purposes (for example, to make chemicals).

Therefore, a full CO₂ life cycle analysis (LCA) of BEVs and FCEVs is required to paint a true picture of the carbon intensity of these vehicles. Some LCA studies are now being published and one of the most thorough is the one carried out by the International Council on Clean Transportation (12) who calculated the g km^–1 CO₂ emissions over the life of the Nissan Leaf BEV (with 30 kWh battery pack, lasting for the life of the vehicle), which they assumed would cover 150,000 km in its lifetime, and compared it to the average and the lowest emitting European cars powered by ICEs. In addition, Toyota have analysed the LCA of a FCEV (14), and these values have been updated for this paper based on Johnson Matthey’s knowledge of the CO₂ emissions when making hydrogen from CH₄ (with and without carbon capture and storage (CCS)).

Figure 2 shows the LCA CO₂ from the European car with average CO₂ emissions in 2017, along with the most fuel efficient ICE-based car in that year (which was in fact a hybrid), together with a BEV being operated on electricity with the EU average CO₂ footprint (the UK’s level is a little lower than this average), and that in Norway, whose extensive use of hydroelectric power reduces the CO₂ emissions during electricity generation to zero. The FCEV LCA is also shown, based on hydrogen generated from steam methane reforming (SMR) with and without CCUS, and based on electrolysis using Norwegian electricity. It is clear that BEVs and FCEVs have significantly lower CO₂ LCA than ICE-based cars today, and this gap will increase further as the carbon footprint of electricity generation continues to drop (see Section 4). (Note that this analysis does not include the recycling or disposal of the vehicles and their components).

Fig. 2.

A very recent BEV vs. ICE life cycle analysis subdivided passenger car GHG emissions into use-phase emissions (from driving the car), and production of all components (including, for example, emissions during mining of raw materials) and end-of-life emissions (15). This study concluded that driving a BEV is already lower in life cycle CO₂ emissions than petrol cars in 95% of the world. The only exceptions are countries such as Poland, where the electricity network is still mostly based on coal-fired power generation. In countries with a heavily decarbonised power system, such as Sweden and France which have large amounts of renewable and nuclear generating capacity, the average lifetime emissions from BEVs are up to 70% lower than petrol cars. In the UK, which is rapidly phasing out coal but still has a reasonable amount of gas-fired power plants, emissions are around 30% lower. The authors also point out that the advantages of BEVs will continue to grow, as power systems around the world become less carbon-intensive. The study projected that by 2050 half of the cars on the roads could be BEVs, leading to a reduction in global CO₂ emissions of up to 1.5 billion tonnes per year, which is the same as the total current CO₂ emissions of Russia.

This focus on LCA is already having a profound impact in the automotive sector. For example, the incoming VW ID.3 BEV is the first vehicle in the company’s history to be built with a CO₂ neutral balance sheet, covering the supply chain (for example, only green energy is used in the production of the battery cells), production (using only green energy at the Zwickau, Germany, manufacturing plant), use phase and recycling, with any currently unavoidable CO₂ emissions being offset by investments in climate protection projects (16).

Governments, states and regions are proposing, and in some cases (such as the UK) committing to, net zero GHG or CO₂ emission targets over the coming years. Indeed, at the time of writing two countries (Bhutan and Suriname) are already carbon neutral, 15 countries have set defined dates to become net zero, and other countries and regions, such as Germany and the EU, are discussing when to implement such a target. Within Europe, Norway plans to become net zero by 2030, Sweden by 2045 and Denmark, France and the UK by 2050. The implications of this are clear: road transport needs to decarbonise rapidly. As outlined above, a 2050 net zero target means that sales of new ICE powered vehicles need to stop by 2040 at the very latest, and preferably at some point during the 2030s, since cars and trucks are often on the road for 10–15 years or more before being scrapped.

This will be a substantial undertaking, requiring all new cars, trucks and buses to be powered by either batteries or hydrogen fuel cells on this timescale. As discussed above, this move to zero (tailpipe) CO₂ or GHG vehicles is only part of the challenge. The electricity used to charge the batteries, and the hydrogen used in the fuel cell vehicles, must also be generated in a very low or zero carbon manner, such as through renewable electricity or advanced CH₄ reforming with CCUS.

Many countries are driving down the CO₂ emissions from power generation. For example, the UK almost halved the carbon footprint of its electricity generation between 2013 and 2017, and one future projected UK pathway to 2050 is shown in Figure 3, from analysis for the National Grid’s Future Energy Scenarios 2019 document (17). This “Two Degrees” scenario foresees significant increases in renewable use, along with a large reduction in natural gas use and the cessation of coal-fired power generation, leading to a reduction in carbon intensity from 120 g CO₂ kWh^–1 in 2019, to just 14 g CO₂ kWh^–1 in 2050. This scenario is consistent with the UK achieving the 2050 decarbonisation target with large-scale centralised solutions.

Fig. 3.

Net zero targets will demand the decarbonisation of road transport (and other forms of transport), and will require strong governmental and regional policies to drive and support the uptake of zero emission vehicles. Extensive public charging and hydrogen refuelling infrastructure will be necessary, and the vehicles must be attractive and affordable options, with features that suit today’s and tomorrow’s lifestyles and transport needs.

The passenger car sector is largely driven by price, convenience and lifestyle: will my vehicle get me comfortably from A to B; can it carry the things I need to take with me; is it a sensible financial choice, in terms of purchase price, fuel price and overall cost of ownership (including likely resale value); and can I easily and conveniently refuel the car after driving the kind of distances that matter to me?

The main questions asked in the commercial vehicle market relate to how this purchase will help the business. The total cost of ownership (TCO) is a critical make-or-break calculation in this sector, as is the requirement for a very high level of vehicle uptime; so a long driving range and rapid refuelling are important here, as is the total load that can be carried by the vehicle.

Given the very different requirements in the two segments, they are considered separately in the subsequent analysis of critical drivers.

5.1 Customer Pull

5.2 Vehicle Price, Ownership Cost, Range and Fuelling Infrastructure

Another important comparison between BEVs and FCEVs is their respective refuelling rate, as shown in Table IV. FCEVs can refuel in around five minutes, corresponding to an energy input per second of around 4 MW which, while slower than the 20 MW typical of gasoline and diesel fuelling, is much faster than that of BEVs, where even Tesla superchargers can only deliver a maximum rate of 0.12 MW. The introduction of ultra-fast chargers is just starting in Europe and North America, with a maximum refuelling rate of 0.35 MW, still a factor of 10 slower than fuelling a FCEV with hydrogen. These differences in fuelling rate are particularly important for some applications, for example high utilisation fleet vehicles and vehicles which do a lot of long distance driving (and heavy commercial vehicles).

There are challenges in both the BEV and FCEV supply chains. For BEVs there are some concerns around Co availability and the ethics around some mines in the Democratic Republic of Congo, where around 50% of the world’s Co is mined. In addition, the projected increases in BEV penetration will likely lead to supply chain pressure on commodities such as Ni (which is a key component in the battery itself) and copper (which is used to move electrons around on the vehicle, and throughout the charging infrastructure), which will put upward price pressure on BEVs. The FCEV supply chain is not well developed today because vehicle volumes are so low, so there is work to do to build the volumes required to support this technology going forward, for example around the fluoropolymer and hydrogen tank components. However, one of the most expensive fuel cell constituents, platinum, already has a highly developed supply chain, and there is plenty of Pt above ground that will be accessible via autocatalyst recycling.

On recycling, the importance of developing cradle‐to-cradle supply chains for future technology has never been greater. There is a legal imperative for vehicle OEMs to ensure their vehicles are extensively recycled, and there are components of high value (and relative scarcity) in both FCEV membrane electrode assemblies (MEAs) and BEV batteries, so it is essential that effective recycling loops are set up going forward. Neither FCEV MEAs nor BEV batteries are recycled to a large extent today, and optimised processes do not exist for either option, but work is ongoing to develop such processes.

A number of factors will determine the proportion of BEVs and FCEVs in the future powertrain mix, with different countries, regions, OEMs and consumers making different choices. There is broad consensus, however, that BEVs are likely to dominate the passenger car ZEV sector, based on their relatively low cost and TCO, the rapidly growing charging infrastructure, the increased range of incoming BEVs and the fact that all major OEMs are bringing attractive BEVs to market over the coming years (and most OEMs also have fuel cell vehicles in small scale production (Honda, Hyundai and Toyota) or have fuel cell programmes in advanced stages of development). FCEVs are likely to play a role in the high mileage, high utilisation end of the passenger car and light commercial vehicle sectors, where their range and refuelling time advantages over BEVs are attractive.

There are many views of the rate at which the global powertrain will shift from the ICE to electrification (BEV and FCEV). LMC, an automotive global forecasting and market intelligence provider, has recently published its view of the evolution of the global passenger car powertrain out to 2050. Their base case scenario (Figure 10(a)) reflects their current “most likely” view of progress in technology, policy and cost, and they see BEVs with the major share in the ZEV space with over 40% of global car sales by 2050. FCEVs, helped by major growth in renewable electricity generation, become significant by 2035, exceeding 20% of global sales by 2050. Hybrids, though squeezed by ZEVs, remain important in some markets, including Japan, and make up around 20% of global vehicle sales in 2050, with the 2050 ICE sales dominated by India.

Fig. 10.

LMC’s “Progressive” scenario (Figure 10(b)) is based on increases in public and political pressure to get the world to act more rapidly to mitigate climate change, leading to more aggressive decarbonisation policies and faster adoption of BEVs and FCEVs. Within this scenario, ICE-only sales cease in the mid-2040s and ZEV sales reach over 90% of demand by 2050, with BEVs accounting for over 60% of global sales, and FCEVs around 30%.

Even this “Progressive” case does not represent a net zero scenario globally, since this would require sales of ICEs, HEVs and PHEVs to stop before 2040, and this scenario still has ICE-containing powertrains making up over 40% of global sales in 2040. However, it could be consistent with a scenario in which Europe moves to net zero in 2050 with the rest of the world following behind and achieving net zero just after 2060.

As outlined above, CO₂ legislation for commercial vehicles is becoming stricter in all the major economies, and on top of the CO₂ regulations, California is planning to introduce a zero emission vehicle mandate as part of its Advanced Clean Trucks regulatory package. By 2030, this will require 15% of Class 7 and 8 trucks (i.e. vehicles over 11.8 tonnes) sold in the state to be zero emission. While batteries are expected to be the technology of choice in the lighter segments, fuel cells are becoming seen as the most likely solution to decarbonise the larger trucks. As in the passenger car sector, governments planning net zero commitments will need to transition their commercial vehicle fleets from diesel to electricity and hydrogen as they move through the 2030s, to ensure a zero emission fleet by 2050.

OEMs are beginning to position themselves for this new reality; for example, Daimler Trucks recently announced that they plan for all new trucks and buses in the triad markets of Europe, Japan and the North American Free Trade Agreement (NAFTA) to be CO₂-neutral when driving by 2039 (i.e. tank to wheels) (29). They plan to achieve this using a combination of BEV and FCEV, with battery electrics in series production by 2022 in all core regions and hydrogen fuel cell-based series production vehicles by the end of the 2020s. Daimler Truck AG and the Volvo Group, two leading companies in the commercial vehicle industry, have signed a preliminary non-binding agreement to establish a new joint venture to develop, produce and commercialise fuel cell systems for heavy-duty vehicle applications and other use cases in the second half of the 2020s. Daimler will consolidate its current fuel cell activities in the joint venture and the Volvo Group will acquire 50% in the joint venture for approximately €600 million (30).

Cummins are also investing in both battery‐based powertrain technology and hydrogen and fuel cells, including acquiring a US$290 million controlling stake in Hydrogenics, a leading fuel cell and hydrogen production technologies provider (31). CNH Industrial have entered into a US$250 million strategic and exclusive heavy-duty truck partnership with Nikola Corporation (32), pioneers in the introduction of zero emission heavy duty trucks powered by hydrogen fuel cell and battery technology. The deal with CNH gives Nikola access to the European commercial vehicle market, as well as to IVECO’s global manufacturing and sales network. In addition, Nikola now has Nel (electrolysis) and Hanwha (solar energy) on board to develop a clean H₂ infrastructure to power these fuel cell vehicles, where conditions allow, supporting the moves towards net zero.

TCO is the critical factor in the long-haul truck sector. Recent analyses by Cummins (33) and AVL (34) have shown that BEV trucks are not viable for this sector due to the high cost, size and weight of batteries for the required range (their weight would reduce payload) and the relatively long recharging time for such large batteries (which would reduce vehicle utilisation significantly). These studies show that the FCEV solution is strongly preferred due to the long range, rapid refueling times and overall TCO. A hydrogen price of €3.50–5.00 kg^–1 is estimated to lead to TCO parity even with today’s diesel-based trucks once such FC trucks are made in significant volumes (100,000 or so); as outlined earlier, the hydrogen price is expected to drop to around €4 kg^–1 by 2030.

In the medium duty distribution truck sector, where driving ranges are lower than in the long‐haul space, BEVs are expected to play a significant role, and for some such distribution applications BEVs already have a lower TCO than current diesel trucks. CARB estimates that the TCO of battery trucks will be lower than diesel trucks by 2024 for many local truck applications (35). They also project that FCEVs will approach the TCO of diesel by 2030.

The development of the fuelling infrastructure for zero emission commercial vehicles is generally regarded as an easier proposition than that for passenger cars, since many commercial vehicles (especially buses and distribution trucks) return to a depot overnight. For BEV-based vehicles this requires charging infrastructure at their home depots and along the parts of the strategic road network along which they operate, for cases where top-up charging away from the depot is required.

For longer distance buses, coaches, and medium and heavy commercial vehicles, the fuel cell powertrain is expected to be widely employed, requiring HRSs at home depots and along the strategic road network. Depot-based HRSs for centralised refuelling have the advantage of increased utilisation, reducing the cost of the hydrogen delivered. A recent report from the Hydrogen Council projects that the cost of hydrogen refuelling infrastructure per vehicle should ultimately drop to below the cost of the BEV recharging infrastructure due to the significant economies of scale available from increasing the size of the distribution network and the introduction of larger retail stations (36). Their analysis led them to conclude that the cost of investment per kilogram of pumping capacity from a HRS will decline roughly 70% over the next 10 years, from about US$6000 for a small station in 2020 to an estimated US$2000 for a large station in 2030. Such a cost trajectory further increases the attractiveness of the hydrogen fuel cell solution for large and longer distance commercial vehicles, since it significantly reduces the TCO of these vehicles.

There are far fewer projections of the future uptake of zero emission commercial vehicles than there are for passenger cars, but it is clear that the commercial vehicle sector needs to develop and implement zero emission vehicles rapidly to support broader decarbonisation initiatives and, particularly, moves to net zero. KGP, a consultancy that provides services to the automotive and related industries worldwide, has developed a “2°C Scenario” for the commercial vehicle market (Figure 11) (37), projecting that the sales of “Electric” commercial vehicles, i.e. those powered by BEV and FCEV, would need to increase from around 87,000 in 2019 to over one million per year by 2030, to be on a trajectory to enable the GHG emissions from the commercial vehicle sector to be aligned with the Paris Agreement’s aim of limiting the global temperature increase due to GHG emissions to 2°C above pre-industrial levels. This level would correspond to around 25% of new sales of commercial vehicles globally.

Fig. 11.

The recent report from the IPCC (2) recommends that the target temperature increase should be at or below 1.5°C, implying that a faster rate of uptake of zero emission commercial vehicles will be required. Approaches to increase ZEV penetration include increasing the stringency of CO₂ tailpipe regulations, and introducing mandates for ZEV fleet levels (such as those proposed within the Advanced Clean Trucks rule by CARB). Interestingly, 30 businesses including Nestle and Unilever recently signed a letter to the new European Commission president Ursula von der Leyen and new EU climate chief Frans Timmermans, calling for legally binding zero-emission truck and van sales targets for 2025 and 2030 (38). They pointed out that these sales targets need to be ambitious, to drive a huge increase in the supply of zero-emission vehicles compared to a business-as-usual scenario, and to put Europe on track to meeting its 2030 climate targets. The businesses believe that binding sales targets will accelerate the uptake of zero-emission vehicles, make air in cities cleaner, put European vehicle-makers at the forefront of innovation while at the same time making Europe less dependent on oil imports. The signatories also say that the EU’s 2030 emissions reduction target must be increased to 55% and the bloc should go climate-neutral by 2050; the latter is the target already proposed by the European Commission.

Overall, therefore, the commercial vehicle sector is becoming increasingly aware of its need to develop zero emission vehicles to play a major role in the decarbonisation of road transport, and extensive work is underway to develop and bring such vehicles to market. Governments and regulators have a significant role to play in creating the right policy framework to drive the initial introduction of such vehicles into the marketplace, and then to encourage their further uptake to enable net zero and air quality targets to be achieved.

The demand for cleaner urban air and massive reductions in CO₂ and other GHG emissions is increasing both from the public and from regulators and governments in many countries and regions. Net zero GHG targets have been set and legislated in several geographies, and more are clearly going to follow in the coming months and years. Transportation is currently a major emitter of criteria pollutants (including CO, hydrocarbons, NOx and PM) and of CO₂, and the decarbonisation of this sector requires the transition from ICE‐powered vehicles to battery electric and fuel cell electric zero emission powertrains. Of course, the minimisation of the carbon footprint of such vehicles is contingent on the electricity and hydrogen used to fuel them being low or zero carbon. In the case of BEVs this means the electricity grid needs to be decarbonised, and this is occurring at good pace in many countries, accelerated by the ongoing reductions in the cost of renewable energy derived from, for example, solar and wind. For FCEVs it means decarbonised electricity to generate green hydrogen by the electrolysis of water, and the addition of CCUS technology to advanced reforming plants, to convert CH₄ into blue (low carbon) hydrogen. The low carbon hydrogen infrastructure and distribution network will constitute part of the transition towards a broader hydrogen economy in many countries, supporting moves to net zero across industry, power generation (including seasonal energy storage to enable increased renewable power generation) and heating for buildings, as well as transportation.

The decarbonisation of the passenger car sector will be driven by rapid uptake of BEVs, which will occur as their purchase costs continue to fall, their driving range continues to increase, and the required charging infrastructure is rolled out worldwide. BEVs are also expected to play a significant role in urban bus and distribution truck applications. FCEVs are expected to dominate the long haul trucking segment as it decarbonises, due to their cost, weight, range and charging time advantages over battery-based technology. They will also likely play a role in inter-city buses and distribution trucks, and in larger passenger cars and sport utility vehicles (SUVs) for applications and customers requiring a long driving range and rapid refuelling.

There is no doubt that net zero targets at the state, country and regional level will be challenging to meet on the 2050 timeframe recommended by the IPCC, but the surface transportation sector is developing and introducing the technologies to enable this. As long as governments and regulators put in place an appropriate set of policy measures and incentives to encourage the early implementation and subsequent mass uptake of zero emission vehicles, the car, van, bus and truck segments will make a huge contribution to global moves towards decarbonisation and the development of net zero economies worldwide.

Outdoor air pollution is linked to an estimated 4.2 million deaths each year worldwide (1). Tailpipe emissions from conventional internal combustion engine (ICE) vehicles are a major contributor to urban air pollution, and as such have been subject to ever tighter legislation for decades, requiring increasingly innovative improvements and catalytic emissions controls. We have now reached the point where a move away from the ICE is required to continue air quality improvements, with several countries going so far as banning new purely ICE vehicles in the coming years. This is where EVs will play their part – both pure EV and hybrid systems powered by LIB technologies, as well as fuel cell technologies, are set to see increased uptake and demand as we strive for cleaner air. In this article, we will add to the automotive-focused literature (2–4) and review what technologies are required to drive the uptake of pure EVs, and what the industry is doing now to respond to consumer requirements as this market rapidly grows.

There are several characteristic battery parameters that it is important to consider and contrast with consumer behaviours and expectations for automotive applications: perhaps most significant, the energy or capacity of the cell equates to the ‘miles in your tank’, and is an area where EVs have lagged behind the ICE in previous years. This is evolving, with the most successful EVs on the market now having an average range of 350 km (5). Range anxiety, equating to energy density, is a major theme for the battery materials industry, with contributions from and innovations required in three areas: the cathode, anode and electrolyte. Cost is also an important factor; as well as the material costs for the active components, analysis has shown that the electrode thickness within the cell is a major contributor to automotive cell costs (6) – materials with increased volumetric energy density are therefore additionally attractive from this perspective. There is also the practical cost benefit afforded by developing systems that can operate at higher voltage cut-offs (7), owing to the usable advantages, towards which multiple cell components can be developed and optimised. Herein, we review one topic of significant industry focus from each area: high-Ni cathode materials, with lithium nickel manganese cobalt oxide (NMC) 811 and beyond being commercialised within the next three years; high energy silicon anode technologies, expected to be at commercial scale in the next three to five years; and solid-state electrolytes, with significant progress expected from the next five years and beyond.

Whilst the cathode active material technology landscape remains diverse, with no one material that will meet all EV requirements, the general trend for passenger EVs is using high-Ni NMC, and lithium nickel cobalt aluminium oxide (NCA) materials. The layered Li Ni oxide (LNO), has been studied for the past 25 years, ever since the commercial application of the isostructural Li Co oxide (LCO) by Sony, Japan, in 1991; the relative low cost of Ni compared to Co was an initial driver for this work – and continues to be a factor today (8–12). Until relatively recently, automotive industry uptake was focused on lower Ni NMC variants, such as LiNi_1/3Mn_1/3Co_1/3O₂ (NMC 111), and lower energy chemistries such as Li Mn oxide (LMO), and Li iron phosphate (LFP). Tesla, USA, bucked the trend; as an early adopter of higher‐Ni NCA materials, it was ahead in the EV mileage stakes. Now, driven by consumer demand for more range, high-Ni is in vogue – the key for research and industry alike is to innovate-out the technical problems associated with LNO regarding its stability.

LNO tends towards non-stoichiometry, owing to the relative instability of Ni³⁺ compared to Ni²⁺, and the similar ionic radii of Ni²⁺ (0.69 Å) and Li⁺ (0.73 Å) (12, 13). It has been shown that synthesis conditions are key to prevent the formation of Ni²⁺ anti-site defects, with near-stoichiometric LNO requiring control of calcination temperature, atmosphere and Li content (12, 14). LNO is also known to undergo several phase transformations on electrochemical cycling; whilst a capacity of over 200 mAh g^–1 can be achieved, these transformations lead to significant capacity fade over the first cycles (15). Early research showed the benefits of incorporating relatively small amounts of other metals, most notably Co, Al and Mn, into the structure to impart stability and significantly improve capacity retention. Owing to the isostructural nature of its end members, all compositions in the series LiNi_1–x Co_x O₂ (x = 0–1) can be formed; Co³⁺ imparts stability by hindering the formation of Ni²⁺ anti-site defects (16). Conversely, doping Mn into the LNO structure has been shown to detrimentally effect the reversible capacity but to impart thermal stability benefits – a key property for battery safety (17, 18). The beneficial effect of Al substitution at low levels is two-fold: an improvement in capacity retention by minimising detrimental phase transformations and an increase in thermal stability (18, 19). There is, however, a limitation to the amount of Al that can be usefully incorporated into the structure; the addition of high-levels of an electrochemically inactive dopant will result in a reduction in capacity, and Al³⁺ has been shown to segregate and create localised defects within the lattice, due to the different ionicity of Al–O and Ni–O bonds (20).

This combined work has ultimately led to continued focus on the multiple metal dopant strategies found in NCA and NMC, where greater benefits are observed than in single dopant systems. Whilst not as catastrophic as those in LNO, NCA and high-Ni NMC materials (such as NMC 811) undergo significant structural changes on cycling, which their lower Ni counterparts (for example NMC 622, NMC 111) do not (Figure 1): at high states of charge, a transformation from the second hexagonal phase (H2) to the third hexagonal phase (H3) occurs in high-Ni materials that is associated with c lattice contraction and capacity fade (21–23). The addition of dopants to the bulk structure of LNO such as cobalt, manganese, aluminium, magnesium, titanium and combinations thereof has been shown to influence stability by affecting the volume change on cycling associated with the H2/H3 phase transformation (24–26).

Fig. 1.

Coating strategies have been employed to high‐Ni NCA and NMC systems, providing benefits in two key areas: handling and performance. The handling and processability of high-Ni materials is a well-known challenge, with surface reactivity towards the ambient resulting in the formation of Li hydroxide and Li carbonate impurities, and the resultant propensity of electrode slurries to gel: this creates obvious challenges before materials have even reached the cell (27–29). Once in the cell, these surface impurities contribute to resistance growth and side reactions resulting in gassing (30, 31). Moreover, the high-Ni surface itself is known to undergo phase changes upon cycling, with the formation of the rock salt phase Ni oxide also contributing to instability and capacity fade (32, 33). In its simplest sense, the application of an inactive coating such as Al oxide passivates the surface with respect to these undesirable side reactions, creating more benign materials that are easier to handle; but only so much of this type of coating can be applied before either significant capacity loss or resistance gains are observed (34). As such, the move toward active coatings, where the removal of an inherent risk of capacity loss does not limit the amount or depth of coating that can be applied, is very attractive. A notable example in this area is the extensive work by the Sun group, who have developed several generations of active coatings and complex morphologies for high-Ni materials (Figure 2): starting with a core@shell strategy, a low-Ni NMC was applied to the surface of a high-Ni NMC, creating a system that combined a high-energy core with a high-stability surface and building a system that was electrochemically active throughout (35). The drawback of this system was the observation that the shell layer broke away from the core on cycling, due to the mismatched volume changes within the core and shell NMC layers. To counteract this, the group developed a gradient coating strategy, whereby a lattice expansion or contraction mismatch was avoided by creating a continuous region of gradual compositional change, thus removing a core@shell interface (38). The Sun group further extended this work to look at deeper and multi-component gradients and their potential benefits (36, 37, 39). Such gradient systems can be viewed as a sophisticated hybrid between bulk doping and surface coating strategies, helping to mitigate the trade-offs associated with each strategy alone.

Fig. 2.

These gradient systems demonstrate the importance of considering morphology and process alongside composition in materials engineering. Another area of interest is the mitigation of microcrack formation through the control of primary particle shape, size and interfaces; fewer cracks means a more stable cathode electrolyte interface (CEI) layer, alleviating resistance growth and gas-generating side reactions (33, 40, 41). Most recently, this has led to particular interest in single crystalline morphologies, which promise greater long-term cycling stability compared to their polycrystalline counterparts by minimising the number of interfaces where microcracks can occur. The majority of published research in this area has focused on lower-Ni NMCs (i.e. NMC 622 or less), where reduction in gassing has been observed compared to polycrystalline counterparts, albeit at the cost of rate capability (42, 43). This lower Ni focus is in part due to the challenging nature of high Ni synthesis at the typically elevated temperatures required to form single crystalline materials compared to those used to generate polycrystalline materials. There are examples demonstrating similar advantages for a single crystalline morphology with up to 80% Ni content and efforts are clearly growing in this area: single crystalline NMC 811 has been shown to exhibit less gassing than its polycrystalline counterpart during high temperature storage (30). Zhu et al. undertook a broad study looking at NMCs from NMC 111 to NMC 811 prepared by multiple approaches and demonstrated the need to tune synthesis conditions to Ni content (44).

The engineering opportunities to overcome the challenges presented by high Ni materials continue to grow. As the automotive industry strives for higher energy, the drive to increase the Ni content of NCA and NMC type materials is clear – the common theme across the industry is to move from NMC 622 to NMC 811 and toward 90% Ni content to meet energy requirements, but also to reduce the Co content required, due to sourcing and cost challenges. Ultimately, a combination of the strategies reviewed above are required to develop and commercialise materials with a Ni content of 80% and above to meet the energy and stability requirements of the automotive industry.

Aligned with the drive toward higher energy cathode materials, there is a requirement to enhance and optimise LIB anode materials toward greater energy density, improved cycle life, lower cost per kilowatt hour and improved gravimetric and volumetric densities (3, 46). In particular, the use of higher energy cathode materials allows increased ampere hour per geometric area and volume of active cathode which is important to retain realistic active material loadings and thicknesses and achieve battery EV (BEV) cell and pack targets. A commensurate improvement in storable energy per area and volume of anode electrode is therefore also required. Cell manufacturers and original equipment manufacturers (OEMs) are increasingly moving beyond todays natural and synthetic graphite materials (or combinations of these) toward blending graphite with a higher energy density Si or Si oxide component to enhance cell level energy gravimetric and volumetric density (47). Table I illustrates examples of such Si containing materials (48).

The high natural abundance of Si and low operating voltage (0.2 V discharging potential compared to Li/Li⁺) single out Si as a highly promising anode material for LIBs (49). However, Si containing materials as battery anodes exhibit a number of challenges, with the greatest of these being significant volume expansion during the lithiation process (see Table I). Particle cracking or fragmentation, loss of electrical contact, ongoing parasitic reactions between electrolyte and ‘fresh’ surfaces, cell swelling and gassing all contribute to cycle life issues (see Figure 3 and Figure 4) (46). Various approaches can be deployed to address the volume change issue for pure Si anodes, including nano-engineering of the Si electrode structure (nanowires and nanoparticles, formation of secondary agglomerates) along with advanced binder combinations to create a flexible electrode structure (46, 50, 51). The addition of carbon dioxide into pouch cells has also been trialled to limit parasitic reactions (52). Formation of nanocomposites of Si–C via mechanical or chemical deposition processes, addition of other alloying components or the choice of a SiO_x material (where first cycle lithiation allows an irreversible reaction creating stabilising LiO_x and Li silicate components within the structure) can all bring improvements (50, 53). Incorporation of conductive carbon also addresses the challenge posed by the intrinsic low conductivity of Si containing materials (54).

Fig. 3.

Fig. 4.

A strategy of blending Si containing materials with existing graphite types is already in progress to achieve moderate capacity increase and lessen volume change, as illustrated by cell level calculations for this approach (for example Si:C 1:3 with capacity of 1100 mAh g^–1 by Andre et al.) (3, 47). Table I illustrates an additional challenge present in Si containing anodes in the form of lower first cycle efficiency (FCE) vs. graphite, related to reactions consuming Li between the electrolyte and anode, the formation of the SEI and associated reduction in useful Li inventory in the working cell, reducing effective watt hour per kilogram. Pre-lithiation approaches, where sacrificial Li containing materials are added to the Si anode during electrode fabrication or strategies such as electrochemical pre-lithiation of formed electrodes ahead of cell assembly are possible (55, 56) along with chemical pretreatments ‘artificial SEI formation’ (57, 58). However, these all represent additional steps and cost in a cell manufacturing process, also pre-lithiated materials and electrodes and Si nanoparticles require careful handling due to the reactivity of the materials with moisture and air (48).

Careful optimisation of the liquid electrolyte additives is also crucial to achieve prolonged cycle life and good FCE, with fluorinated additives, especially fluoroethylene carbonate (FEC), showing benefit (59). The discharge and charge voltage profile of Si containing anodes is slightly different to graphite-only examples, leading to reduced chance of Li plating during charging in Si anodes, but typically slightly lower discharge voltage with graphite, thus adjustments to cell balancing and understanding of the operational state of charge window in the usable voltage range are important for full cell (60).

Assessment of the sustainability of changing to Si containing anode components and advanced higher energy cell chemistries is also vital as electrification of the power train advances worldwide (61).

A further driver to increase the energy density of cells is to replace existing anode materials with metallic Li. Li metal was used as the first anode material in rechargeable Li-ion cells due to its very high energy density (3860 mAh g^–1) and low electrochemical potential (–3.040 V vs. the standard hydrogen electrode). However, numerous challenges prevented its widespread adoption, including low cycle life predominating from issues such as the formation of dendrites and unstable solid-electrolyte interfaces. Recently, there has been increasing investigations into using solid-state electrolytes to mitigate the challenges of using metal anodes, whilst maintaining their advantages.

In addition to potentially enabling the use of Li metal anodes, the evolution to solid state batteries has other advantages to conventional Li-ion cells (62). The primary reason is the displacement of the highly flammable cocktail of organic electrolytes that is used currently. This both reduces the risk of unwanted thermal events in the instance of cell misuse or damage, but it also results in a simpler packaging, further increasing the energy density (63) (Figure 5). In addition, solid state materials could offer increased electrochemical stability windows in comparison to existing organic electrolytes; potentially enabling alternative materials, such as higher voltage cathode materials, to be deployed.

Fig. 5.

The use of polymers as electrolytes in batteries was first pioneered in the 1970s (64, 66). This enables cells with high degrees of safety to be manufactured in various form factors. Polymer-based systems such as polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyacrylonitrile and polymethyl methacrylate (PMMA) based electrodes have all been widely studied as polymer electrolytes (67). PEO-based polymer electrolytes have been studied the most due to their advantageous properties including lower cost, ability to solvate a wide variety of ions, relatively high chemical stability and the use of their moderate mechanical strength (~10⁶ Pa) to supress the growth of dendrites (68, 69). However, the low conductivity (~10^–7 S cm^–1) of the electrolyte systems, due to the crystallinity of the polymer chains, has been a limitation (70). Overall, the general uptake of polymer gel cells has been restricted by their lower energy densities and poor electrochemical stability compared to liquid electrolytes.

More recently, researchers have explored a range of solid inorganic materials, which allow ionic mobility through the solid. Numerous classes of these are currently being explored, all possessing different advantages and disadvantages (63, 71, 72). A summary of these are highlighted in Table II.

Researchers have looked to examine inorganic electrolyte materials with high ionic conductivities, such as Li₁₀GeP₂S₁₂, which exhibits high conductivity at RT (73). However, sulfide-based solid electrolytes are generally expensive, more challenging to synthesise and are sensitive to moisture, potentially releasing toxic gases. This brings challenges in their handling and subsequent fabrication.

Although most solid electrolytes have been shown to react with Li metal, garnet materials (such as Li₇La₃Zr₂O₁₂ (LLZO)), have shown the greatest stability (74, 75). In addition, they have relatively low costs and a wide electrochemical window (~6 V vs. Li metal) potentially enabling the use of higher voltage cathode materials; and are therefore attracting increasing investigations (74). The cubic phase of LLZO is found to offer greater ionic conductivity than the tetragonal phase. A typical strategy to promote this is to dope elements such as Al, tantalum and gallium into the structure thus stabilising the highly conductive cubic phase at RT (76).

Despite these advantages, a challenge in using LLZO remains its instability in the ambient atmosphere, due to CO₂ and moisture (77). This results in increased complexity upon subsequent material handling and processing. Further challenges include poor interfacial compatibility of LLZO with electrodes. To overcome this, methods to increase the wettability of the electrolyte have been explored, such as the atomic layer deposition of Al₂O₃ to reduce interfacial resistance by the formation of a desirable Li-Al-O layer (73); or alloying Li with other elements (such as Si, Al, Ge) to increase compatibility (72).

In addition to the preparation of materials capable of high levels of Li-ion conductivity, it is vital that these materials can be manufactured at an industrial scale at a reasonable cost. While there has been considerable interest in the use of oxides for an all solid electrolyte, their brittleness and fragility impose new challenges for mass production (78, 80). As a result the scale up of such activities is being explored using a variety of different processing technologies (Figure 6). Mature slurry-based technologies have been shown to provide dense layers using high throughput techniques. However, subsequent high temperature sintering inhibits the co-firing of solid electrolytes and cathode particles.

Fig. 6.

When using Li metal as an anode material it is vitally important to prepare dense electrolyte layers in the absences of holes. It has been suggested that a critical relative density of >93% are required to eliminate the formation of dendrites in LLZO electrolytes (79); with short circuits believed to propagate through voids and grain boundaries (81). To obtain highly sintered garnet-based solid electrolytes by conventional sintering techniques, generally high temperatures (>1200°C) and long sintering times (>30 h) are required. Such conditions can result in the decomposition of the solid electrolytes and loss of Li from the structure.

To overcome these challenges, alternative processes such as hot pressing, field-assisted sintering and spark plasma synthesis have been investigated to fabricate the optimal dense ceramic layer (82–85). To that end further evaluation of deposition and sintering technologies will be required to provide an economically viable solution.

There are also multiple technologies (such as Li‐sulfur and Li-air chemistry) that have the potential to deliver significant advances in performance, such as increased energy density (86). For example, Li-S chemistry benefits from the low cost and high abundance of S and an energy density significantly higher than current Li-ion cells (~2500 Wh kg^–1) (87, 88). However, these technologies currently suffer from technical challenges that limit their uptake. To fully maximise the benefit of these technologies, it is necessary to overcome the challenges of working with a Li metal anode. The use of solid-state electrolytes is a recent area where people have been exploring with the aim of enabling the technology via anode protection.

The demand for cleaner air is accelerating and this is giving rise to increased electrification in the automotive drivetrain. There is also a growing acceptance of vehicles with varying degrees of electrification, and this trend looks set to continue. Current concerns for increased energy density to counter consumer’s ‘range anxiety’ are leading to material developments to meet this. In particular, the careful design and manufacturing of cathode materials with high amounts of Ni and anode materials with increasing Si content are steadily improving these key parameters. Furthermore, significant exploration into next generation technologies, such as solid-state electrolytes, opens the possibility of redesigning the cell. While options to the type of material used and their processing remain; the replacement of conventional liquid electrolytes promises to deliver further improvements in energy density as well as other benefits, such as safety performance. These three examples highlight the major trends being investigated and introduced into automotive cells to meet the demands of society.

The tremendous growth of the global economy is directly related to increased energy demand and (currently) high greenhouse gas emissions. Substantial reduction in global emissions is required to minimise environmental hazard and ongoing climate change. Legislations are pushing for energy transition, replacing fossil fuels with alternatives for reduced emissions. Wind, solar and biomass are key-players for the energy future, as depicted in the latest statistics and forecast (1, 2). According to one of the possible energy transition scenarios, to accommodate the increasing energy demands with the least environmental impact, renewable sources will rapidly grow their share in the energy mix, while natural gas is foreseen to maintain a key role during the transition phase (1, 2). However, natural gas contributes to CO₂ emissions, with approximately 7 billion tonnes of CO₂ being produced on a yearly basis, with approximately 5% of this amount attributed to flaring (Figure 1). This percentage adds to both the environmental problem and to the waste of an important resource, methane (3–5).

Fig. 1.

ADREM (EU project Horizon 2020 No. 636820), focused on the development of novel reactor concepts that are capable of converting methane to higher chemicals with a compact, modular and flexible process design. The University of Zaragoza (UniZar), Spain; Delft University of Technology (TU Delft), The Netherlands; and SAIREM, Décines-Charpieu, France, investigated microwave reactor technology for methane non-oxidative coupling (MNOC). Katholieke Universiteit Leuven (KU Leuven), Belgium and Kemijski inštitut in Ljubljana, Slovenia, worked with plasma technology for methane non-oxidative coupling and dry reforming respectively. Ghent University, Belgium, investigated the gas solid vortex reactor (GSVR) for oxidative methane coupling (OCM). In the present paper, we give an overview of the technologies that were developed, the status, the main bottlenecks and the path forward.

2.1. Microwave Non-Oxidative Methane Coupling with Both a Multistage Monomodal Reactor and with a Travelling Wave Reactor

2.2. Plasma Non-Oxidative Coupling of Methane

2.3. Oxidative Coupling of Methane with a Gas-Solid Vortex Reactor

2.4. Plasma Dry Reforming

To assess the potential of the reactors that were developed in ADREM, a case study of valorising associated (flared) gas has been simulated. The feed is rich in methane (>95% vol) with a flowrate of 1000 Nm³ h^–1. All the cases include pretreatment for sulfur and CO₂ removal, while for comparison purposes, the downstream processing follows the conventional approach, with either cryogenic separation (for C2+ hydrocarbons) or methanol loop (for syngas to methanol conversion). The end product consists either of mixtures of products (i.e. ethane/ethylene) or product at low purity (for example, raw methanol). Further purification in centralised units is necessary to reach the required quality.

The specific energy (Table I) of each technology consists of the reactors’ energy demands and the downstream processing (DSP) intensity (the latter being directly related to methane conversion and productivity). The microwave and GSVR technologies have the lowest specific energy consumption, as a result of the upscaled microwave reactor design of SAIREM and the exothermic OCM reaction respectively. The plasma technology is more energy intensive predominantly due to numbering up of the modules in order to accommodate the required flow. The technologies that produce BTX and ethylene would obviously benefit from replacement of the cryogenic separation by energy-efficient and modular alternatives (for example, ethane/ethylene membranes (14) or adsorption based technology) to decrease the energy demand. For the plasma dry reforming, the product syngas enables alternative downstream processing (for example, a methanol reactor), but the high operational pressure of such a design still adds to the overall energy efficiency and complicates the modularity of the plant. However, the modular methanol reactor is already available in commercial scale (3).

The capital intensity (Table I) is a function of the conversion and selectivity and the ease of upscale. On one hand, low conversion results in a large recycle flow (due to unconverted methane), and more energy-demanding units. On the other hand the numbering up strategy to accommodate the required throughput implies high capital requirements for all the technologies. The MW reactor with the realised upscaled concept and the GSVR that can accommodate high flowrate, appear to be the most cost-competitive at the present development stage. Collectively, the first step of further development for the ADREM reactors is to improve the reactor performance in terms of conversion and selectivity.

Compared to flaring, for all the technologies the CO₂ emissions are low (25–80% decrease, depending on the technology), with the highest CO₂ emissions coming from the GSVR reactor (where CO₂ is a product) and the lowest emissions coming from plasma dry reforming (where CO₂ is the reactant). Applying the ADREM technologies in situations associated with gas flaring in remote locations will have a huge environmental benefit when renewable electricity is available in abundance.

During the project, partners have been developing new small scale gas-to-liquids (GTL) technology, where methane is valorised to chemicals. Two of the reactor technologies have been successfully demonstrated in TRL 5 (microwave and plasma). With tighter regulation on greenhouse gas emissions and flaring, there are clear opportunities for the ADREM technologies to find applications. The UniZar reactor has efficiently been upscaled (32x) and the GSVR reactor is designed in such a way that it can accommodate relatively high flowrate. The plasma reactors (both NPD and dry reforming) showed the highest conversions and selectivities, but they still need to improve the upscale strategy.

For further upscaling and demonstration of the technologies, it is required to improve productivity, conversion and mitigation of carbon formation. Different operating conditions (in terms of pressure, temperature, catalysis or reactor geometry) or in situ product separation could potentially enable higher conversions and selectivity and are planned for the next steps of development. Improving the reactor performance will decrease the unit size for each technology and simplify the downstream processing. Downstream processing is an essential point that should be developed and optimised once the selectivity and conversion are improved.

In July 2018 the UK government’s Road to Zero Strategy was announced, including the ambition to see at least half of new cars to be ultra low emission vehicles (ULEV) by 2030 (3). ULEVs are vehicles that emit less than 75 g of carbon dioxide from the tailpipe for every kilometre travelled; in practice, the term typically refers to battery EV (BEV), plug-in hybrid EV (PHEV) and fuel cell EVs. This built on the government’s commitment to “end the sale of new conventional petrol and diesel cars and vans by 2040”.

There are over 200,000 ULEVs in the UK as of the second quarter of 2019 (4) and while total ULEV registrations are still low, this is growing rapidly for several reasons, including government tax incentives and consumer appetite for decarbonisation. 2019 saw an 87% year on year increase in BEV registrations and a corresponding decrease in PHEV registrations due to subsidy changes (5). In this article the term EV is used to refer to both BEVs and PHEVs; currently EV stock is split between these two types, however in 2050 we expect most cars to be BEVs.

To model the uptake of various road transport types and fuels in our 2019 FES we utilise a total cost of ownership model. Assumptions on the increase and decrease of various factors including battery costs, fuel costs, vehicle efficiency and subsidies available for different scenarios feed into this model. The uptake rates for the different scenarios, in relation to the expected sales projections for all vehicles (determined by the total cost of ownership and the rate at which older vehicles are scrapped) gives the expected number of low carbon vehicles on the road (Table I).

The slowest growth scenario in FES projects only 2.3 million EVs to be owned in 2030 compared to a maximum of 11.5 million EVs in 2030 in the highest growth scenario. This represents 6.8% and 35% of cars being electric respectively in each scenario. By 2050 we expect almost all cars to be electric in all scenarios, although some petrol and diesel fuelled vans and heavy goods vehicles (HGVs) still exist in the slower decarbonisation scenarios. Although this shift towards EVs will cause an increase in overall electrical energy demand, the greater challenge lies in charging; i.e. where, when and how these vehicles are charged.

Traditionally the grid has been supplied by a relatively small number of large generators, primarily coal, gas and nuclear power stations. The energy system is transitioning from this centralised system where there were under one hundred generators primarily connected to the transmission network with flexible fossil fuel plant to help meet demand peaks, to the current state where there are thousands of smaller decentralised generators such as wind and solar farms mainly connected to the distribution network. Over the past 10 years this growth in renewables has led to new challenges in system operation, with wind and solar generation presenting issues due to generation variability.

Significant progress has been made decarbonising the electricity system since 2010 thanks to this growth in renewable generation. The carbon intensity of electricity is a measure of the level of CO₂ emissions that are produced per kilowatt hour of electricity consumed. The average carbon intensity of electricity has fallen 53% from 529 g CO₂ kWh^–1 in 2013 to 214 g CO₂ kWh^–1 in 2019 (6). The trend in emissions reduction is shown in Figure 2.

Fig. 2.

2.2.1 Phase Out of Coal

2.2.2 Increase in Renewable Generation

The Office of Gas and Electricity Markets (Ofgem), UK, defines flexibility as “modifying generation and/or consumption patterns in reaction to an external signal (such as a change in price) to provide a service within the energy system” (12). Demand on the electricity network varies throughout the day and across seasons. Peak demands are seen on winter weekday evenings, between 5 pm and 7 pm, with minimum demands seen historically overnight during the summer. The country needs electricity capacity to meet peak demand, which is variable, and hence the ability to increase this capacity through flexibility or to decrease the peak is pivotal.

Renewable generation always generates where it can as it has zero marginal cost. This is currently backed up by fossil fuel generation that can be turned up and down as required to help meet demand peaks. Between April and September solar generation meets a larger portion of demand during the daytime; generation is at its peak in the middle of the day when the sun is brightest. Solar generation provides relatively little contribution towards meeting evening peaks in demand, however. Wind generation output depends on the weather systems over the UK but is typically higher in winter. It is highly variable however, and the system needs to be able to manage multi-week spells with low levels of wind generation which can occur when a high-pressure system settles over the UK.

Output from large-scale transmission-connected generation is visible to the ESO and instantaneous changes in generation can be clearly seen and managed. Small-scale distribution-connected generation however, particularly embedded solar, may show up only as reduced demand on the transmission system which can make it difficult to forecast and manage.

To understand the impact of EVs on the electricity system it is necessary to understand how they charge today and how this may change in future. We commissioned a Network Innovation Allowance (NIA) project to develop a comprehensive picture of current charging profiles (14). The study successfully gathered together a database of over eight million real world charge events and generated a representative full year charging demand profile at hourly resolution across a range of different location types and charger sizes. This evaluation has delivered an improved understanding of charging behaviour and enabled us to generate a more nuanced and informed view of the future impact of EV growth on electricity demand.

Existing electricity system peak demand typically occurs between 5–6 pm on weekdays, which is earlier than the peak demand for EV charging (Figure 3). This evening peak in EV demand is dominated by residential charging and is likely the result of commuters plugging into charge when they arrive home from work (it tails off as those vehicles plugged in earlier finish charging). Workplace and public charging contribute to another smaller peak mid-morning on weekdays between 9–10 am. The reduction in workplace charging rates after 10 am suggests that generally commuter vehicles plugged in to workplace chargers when they arrive are fully charged by mid-morning and remain plugged in and no longer charging subsequently until they leave.

Fig. 3.

Other learnings from this study include the effect of temperature on demand, where average kilowatt hour of energy per EV per day increases by 1.6% for each one degree decrease in temperature. During public holidays demand also drops, particularly over Christmas and Easter where, despite an increase in demand at (primarily motorway based) rapid chargers, this is offset by a significant decrease in other types of charging. Weekend demand is also on average 25% lower than weekdays and shows a broader demand profile shape that peaks an hour earlier.

It is clear from the data that current charging patterns will contribute to increased peak loads on the electricity network at both distribution and transmission levels. This may present more of a problem for the distribution network where the existing peak demand is often later than on the transmission network. If charging patterns can be shifted to increase levels of overnight and daytime charging at the expense of evening charging this could have a beneficial network effect and help reduce carbon emissions, as peak demands are more likely to be met by dirtier fossil fuel generation peaking plants.

This study has captured the charging demand of plug-in cars, but as other vehicle segments electrify demand will change. This, for example, includes depot-based vans, taxis and buses that may show different demand profile characteristics and present different opportunities.

As part of FES 2019 we developed four scenarios setting out a credible range for how energy demand and generation could develop out to 2050 (Figure 4). This includes projections of the levels of renewable generation, EV take-up and flexibility.

Fig. 4.

Two of our scenarios met the national decarbonisation target at the time of an 80% reduction in 1990 emissions by 2050. These are Two Degrees, which relies primarily on centralised generation and Community Renewables which has a greater proportion of decentralised generation. The UK government has since tightened the 2050 target to net zero CO₂ emissions. It is likely that new policy and support will be put in place to achieve this aim, therefore we would expect that by 2030 the electricity system would be closer to Two Degrees and Community Renewables than the other two scenarios which did not meet the 80% reduction target. Net zero in 2050 was modelled as a sensitivity in FES 2019 and will be included in core scenarios in FES 2020.

Figure 5 shows the installed electricity generation capacity of different technologies in 2018 and the projected changes to this under the different scenarios in 2030 and 2050. In all scenarios overall capacity grows, but this is particularly noticeable in the faster decarbonising scenarios, Two Degrees and Community Renewables. These two scenarios have a higher proportion of renewable generation and much of this capacity is variable, with a low load factor, meaning more generation capacity is required to meet overall energy requirements at times of high demand, particularly in winter. The total installed capacity significantly exceeds forecast peak demands to account for this. Due to their lower load factor and variability, renewables are de-rated when calculating the capacity required to keep the lights on as they will not always be available to contribute at peak times (15).

Fig. 5.

Figure 5 also shows potential future avenues to add flexibility, with significant increases in interconnector capacity and storage capacity, particularly across the more decarbonised scenarios. Interconnectors will allow the UK to trade more electricity with mainland Europe at times of high demand or excess generation. Shorter duration storage projects could meet small periods of increased demand or provide flexibility services such as frequency response. Longer duration storage is well suited to covering longer periods of, for example, high or low wind, potentially co‐located with generation. Some of the other key outputs from FES 2019 are set out in Table II for 2030.

In the faster decarbonising scenarios of Two Degrees and Community Renewables, the growth of low-carbon capacity will contribute to periods of oversupply of electricity, particularly in the summer months beyond 2030. Inflexible renewable generation capacity will at times produce more electricity than total demand. The annual amount of excess electricity rises to 20–25 TWh (around 6% of total annual output) after 2040 in Community Renewables. Our modelling shows that at times of likely oversupply, excess electricity cannot be exported, as other countries that have decarbonised are likely to be facing similar issues. Nor can it be stored, as available storage is full.

Future markets will determine how this electricity could be used, stored or curtailed in the most efficient way; this could include use of electricity to produce hydrogen or charge EVs. This is likely to be attractive to consumers as power prices will be very low or negative at times of oversupply meaning consumers could be paid to use the electricity when carbon emissions are also likely to be low.

National Grid ESO has developed a Carbon Intensity forecasting tool (Figure 6) (6) in partnership with Environmental Defense Fund Europe, UK, University of Oxford Department of Computer Science, UK, and the World Wide Fund for Nature (WWF), Switzerland. It uses machine learning and power system modelling along with Met Office, UK, data to forecast the carbon intensity and generation mix 48 h ahead for each region in Great Britain. The forecast carbon intensity figures are accessible via a website, the National Grid ESO app and an application programming interface (API) to allow developers to produce applications that will enable consumers and smart devices to optimise their behaviour to minimise carbon emissions. WWF have implemented the API into a widget that can help people plan their energy use, switching devices on when energy is green and off when it is not.

Fig. 6.

The data from our EV innovation project suggests that EVs typically spend long periods of time plugged into residential or workplace charge points and current charging patterns result in vehicles starting to charge as soon as they are connected to the charger with little to no smart management of charging. Smart charging enables consumers to manage the time when their vehicle is charged. This could be to take advantage of lower prices or lower carbon electricity or to respond to external signals from third parties such as aggregators or network companies.

The government’s Automated and Electric Vehicles Act 2018 (16) sets out requirements for all new charge points sold or installed to be ‘smart’. This means they must be able to receive, process and react to information or signals, such as by adjusting the rate of charge or discharge; transmit, monitor and record information such as energy consumption data; comply with requirements around security; and be accessed remotely. This legislation aims to avoid infrastructure being a blocker to future smart charging developments.

EV batteries can be considered as a form of storage within the wider energy system, though the impact of EVs is fundamentally different to other forms of storage. This is because not all vehicles are connected to the system at any point in time, meaning that the available storage capacity from EVs is constantly varying. This creates natural diversity in availability and charging behaviour for EV batteries and means that the potential for EVs to increase, shift or decrease demand varies and is a fraction of the total capacity of EV batteries in Great Britain at any one time. BEV batteries are typically five to 10 times larger than PHEV batteries, so the relative mix of PHEVs to BEVs will also affect the total energy capacity available.

Consumers can be incentivised to take part in smart charging and delay the start of their charging period through time-of-use (ToU) tariffs and be guided by tools such as National Grid ESO’s Carbon Intensity app; these are already available to consumers to allow them to schedule their EV charging for times of lower prices or carbon emissions. A more dynamic form of smart charging involves in-home automation and smart management and optimisation of charging while the vehicle is plugged in without active involvement from the consumer. This would remove barriers for consumers to get involved and have a significant impact on the electricity system and resulting carbon emissions. This will become more important as the number of EVs on the system grows. These ToU tariffs are already available for consumers from some innovative energy suppliers such as Octopus Energy, UK, and are expected to become more widely available over time.

An additional avenue for EV to have a positive impact on the electricity network is through the use of V2G technology. This is where electricity stored in the battery of an EV can be supplied back into the network through a two-way V2G enabled charger. This process is likely to be managed by an aggregator triggering response from a large portfolio of vehicles contracted to deliver this capability, they would likely offer financial incentives to consumers to facilitate this. Individuals and businesses could also use this to take advantage of variable rate tariffs without the third-party involvement. There are a range of pilot projects developing this technology; in 2017 the UK’s innovation agency, Innovate UK, committed £25 million in support to eight real world V2G demonstrator projects undertaken by a range of organisations including energy suppliers, network operators and small and medium-sized enterprises (SMEs) (17).

Battery lifetimes are typically measured in the number of discharge cycles they can undergo without battery capacity falling below a certain threshold. The measurable impact of V2G on battery health is still at the research stage, with recent papers providing seemingly contradictory conclusions. Dubarry et al., 2017 (18) showed that additional battery cycling due to V2G would shorten battery life; while Uddin et al., 2017 (19) indicated that battery degradation could be avoided. These authors have since published a joint study in which they “jointly reconcile their previous conclusions by providing clarity on how methodologies to manage battery degradation can reliably extend battery life” (20). It is clear, however, that further research in this area is necessary to determine the effects of V2G and ensure it is an attractive proposition for both electricity networks and consumers.

Our FES 2019 scenarios consider how engaged vehicle owners are likely to be with smart technology and V2G and build these assumptions into our modelling of peak demand. We classify a consumer as participating in smart charging if they actively choose not to charge their EVs at peak times, wherever possible. We assume that only 2% of vehicle owners engage in V2G through to 2030 as the technology is still at an early stage, however that number then steadily increases to 2050, with the highest levels in the Community Renewables scenario. These participation rates are shown in Table III.

3.4.1 Impact on Peak Demand

3.4.2 Impact on Oversupply of Renewable Generation